block, bfq: add more fairness with writes and slow processes

[mirror_ubuntu-bionic-kernel.git] / block / bfq-iosched.c

/*
 * Budget Fair Queueing (BFQ) I/O scheduler.
 *
 * Based on ideas and code from CFQ:
 * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
 *
 * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
 *                    Paolo Valente <paolo.valente@unimore.it>
 *
 * Copyright (C) 2010 Paolo Valente <paolo.valente@unimore.it>
 *                    Arianna Avanzini <avanzini@google.com>
 *
 * Copyright (C) 2017 Paolo Valente <paolo.valente@linaro.org>
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License as
 *  published by the Free Software Foundation; either version 2 of the
 *  License, or (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  General Public License for more details.
 *
 * BFQ is a proportional-share I/O scheduler, with some extra
 * low-latency capabilities. BFQ also supports full hierarchical
 * scheduling through cgroups. Next paragraphs provide an introduction
 * on BFQ inner workings. Details on BFQ benefits, usage and
 * limitations can be found in Documentation/block/bfq-iosched.txt.
 *
 * BFQ is a proportional-share storage-I/O scheduling algorithm based
 * on the slice-by-slice service scheme of CFQ. But BFQ assigns
 * budgets, measured in number of sectors, to processes instead of
 * time slices. The device is not granted to the in-service process
 * for a given time slice, but until it has exhausted its assigned
 * budget. This change from the time to the service domain enables BFQ
 * to distribute the device throughput among processes as desired,
 * without any distortion due to throughput fluctuations, or to device
 * internal queueing. BFQ uses an ad hoc internal scheduler, called
 * B-WF2Q+, to schedule processes according to their budgets. More
 * precisely, BFQ schedules queues associated with processes. Each
 * process/queue is assigned a user-configurable weight, and B-WF2Q+
 * guarantees that each queue receives a fraction of the throughput
 * proportional to its weight. Thanks to the accurate policy of
 * B-WF2Q+, BFQ can afford to assign high budgets to I/O-bound
 * processes issuing sequential requests (to boost the throughput),
 * and yet guarantee a low latency to interactive and soft real-time
 * applications.
 *
 * In particular, to provide these low-latency guarantees, BFQ
 * explicitly privileges the I/O of two classes of time-sensitive
 * applications: interactive and soft real-time. This feature enables
 * BFQ to provide applications in these classes with a very low
 * latency. Finally, BFQ also features additional heuristics for
 * preserving both a low latency and a high throughput on NCQ-capable,
 * rotational or flash-based devices, and to get the job done quickly
 * for applications consisting in many I/O-bound processes.
 *
 * BFQ is described in [1], where also a reference to the initial, more
 * theoretical paper on BFQ can be found. The interested reader can find
 * in the latter paper full details on the main algorithm, as well as
 * formulas of the guarantees and formal proofs of all the properties.
 * With respect to the version of BFQ presented in these papers, this
 * implementation adds a few more heuristics, such as the one that
 * guarantees a low latency to soft real-time applications, and a
 * hierarchical extension based on H-WF2Q+.
 *
 * B-WF2Q+ is based on WF2Q+, which is described in [2], together with
 * H-WF2Q+, while the augmented tree used here to implement B-WF2Q+
 * with O(log N) complexity derives from the one introduced with EEVDF
 * in [3].
 *
 * [1] P. Valente, A. Avanzini, "Evolution of the BFQ Storage I/O
 *     Scheduler", Proceedings of the First Workshop on Mobile System
 *     Technologies (MST-2015), May 2015.
 *     http://algogroup.unimore.it/people/paolo/disk_sched/mst-2015.pdf
 *
 * [2] Jon C.R. Bennett and H. Zhang, "Hierarchical Packet Fair Queueing
 *     Algorithms", IEEE/ACM Transactions on Networking, 5(5):675-689,
 *     Oct 1997.
 *
 * http://www.cs.cmu.edu/~hzhang/papers/TON-97-Oct.ps.gz
 *
 * [3] I. Stoica and H. Abdel-Wahab, "Earliest Eligible Virtual Deadline
 *     First: A Flexible and Accurate Mechanism for Proportional Share
 *     Resource Allocation", technical report.
 *
 * http://www.cs.berkeley.edu/~istoica/papers/eevdf-tr-95.pdf
 */
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <linux/cgroup.h>
#include <linux/elevator.h>
#include <linux/ktime.h>
#include <linux/rbtree.h>
#include <linux/ioprio.h>
#include <linux/sbitmap.h>
#include <linux/delay.h>

#include "blk.h"
#include "blk-mq.h"
#include "blk-mq-tag.h"
#include "blk-mq-sched.h"
#include <linux/blktrace_api.h>
#include <linux/hrtimer.h>
#include <linux/blk-cgroup.h>

#define BFQ_IOPRIO_CLASSES      3
#define BFQ_CL_IDLE_TIMEOUT     (HZ/5)

#define BFQ_MIN_WEIGHT                  1
#define BFQ_MAX_WEIGHT                  1000
#define BFQ_WEIGHT_CONVERSION_COEFF     10

#define BFQ_DEFAULT_QUEUE_IOPRIO        4

#define BFQ_WEIGHT_LEGACY_DFL   100
#define BFQ_DEFAULT_GRP_IOPRIO  0
#define BFQ_DEFAULT_GRP_CLASS   IOPRIO_CLASS_BE

struct bfq_entity;

/**
 * struct bfq_service_tree - per ioprio_class service tree.
 *
 * Each service tree represents a B-WF2Q+ scheduler on its own.  Each
 * ioprio_class has its own independent scheduler, and so its own
 * bfq_service_tree.  All the fields are protected by the queue lock
 * of the containing bfqd.
 */
struct bfq_service_tree {
        /* tree for active entities (i.e., those backlogged) */
        struct rb_root active;
        /* tree for idle entities (i.e., not backlogged, with V <= F_i)*/
        struct rb_root idle;

        /* idle entity with minimum F_i */
        struct bfq_entity *first_idle;
        /* idle entity with maximum F_i */
        struct bfq_entity *last_idle;

        /* scheduler virtual time */
        u64 vtime;
        /* scheduler weight sum; active and idle entities contribute to it */
        unsigned long wsum;
};

/**
 * struct bfq_sched_data - multi-class scheduler.
 *
 * bfq_sched_data is the basic scheduler queue.  It supports three
 * ioprio_classes, and can be used either as a toplevel queue or as an
 * intermediate queue on a hierarchical setup.  @next_in_service
 * points to the active entity of the sched_data service trees that
 * will be scheduled next. It is used to reduce the number of steps
 * needed for each hierarchical-schedule update.
 *
 * The supported ioprio_classes are the same as in CFQ, in descending
 * priority order, IOPRIO_CLASS_RT, IOPRIO_CLASS_BE, IOPRIO_CLASS_IDLE.
 * Requests from higher priority queues are served before all the
 * requests from lower priority queues; among requests of the same
 * queue requests are served according to B-WF2Q+.
 * All the fields are protected by the queue lock of the containing bfqd.
 */
struct bfq_sched_data {
        /* entity in service */
        struct bfq_entity *in_service_entity;
        /* head-of-line entity (see comments above) */
        struct bfq_entity *next_in_service;
        /* array of service trees, one per ioprio_class */
        struct bfq_service_tree service_tree[BFQ_IOPRIO_CLASSES];
        /* last time CLASS_IDLE was served */
        unsigned long bfq_class_idle_last_service;

};

/**
 * struct bfq_entity - schedulable entity.
 *
 * A bfq_entity is used to represent either a bfq_queue (leaf node in the
 * cgroup hierarchy) or a bfq_group into the upper level scheduler.  Each
 * entity belongs to the sched_data of the parent group in the cgroup
 * hierarchy.  Non-leaf entities have also their own sched_data, stored
 * in @my_sched_data.
 *
 * Each entity stores independently its priority values; this would
 * allow different weights on different devices, but this
 * functionality is not exported to userspace by now.  Priorities and
 * weights are updated lazily, first storing the new values into the
 * new_* fields, then setting the @prio_changed flag.  As soon as
 * there is a transition in the entity state that allows the priority
 * update to take place the effective and the requested priority
 * values are synchronized.
 *
 * Unless cgroups are used, the weight value is calculated from the
 * ioprio to export the same interface as CFQ.  When dealing with
 * ``well-behaved'' queues (i.e., queues that do not spend too much
 * time to consume their budget and have true sequential behavior, and
 * when there are no external factors breaking anticipation) the
 * relative weights at each level of the cgroups hierarchy should be
 * guaranteed.  All the fields are protected by the queue lock of the
 * containing bfqd.
 */
struct bfq_entity {
        /* service_tree member */
        struct rb_node rb_node;

        /*
         * Flag, true if the entity is on a tree (either the active or
         * the idle one of its service_tree) or is in service.
         */
        bool on_st;

        /* B-WF2Q+ start and finish timestamps [sectors/weight] */
        u64 start, finish;

        /* tree the entity is enqueued into; %NULL if not on a tree */
        struct rb_root *tree;

        /*
         * minimum start time of the (active) subtree rooted at this
         * entity; used for O(log N) lookups into active trees
         */
        u64 min_start;

        /* amount of service received during the last service slot */
        int service;

        /* budget, used also to calculate F_i: F_i = S_i + @budget / @weight */
        int budget;

        /* weight of the queue */
        int weight;
        /* next weight if a change is in progress */
        int new_weight;

        /* original weight, used to implement weight boosting */
        int orig_weight;

        /* parent entity, for hierarchical scheduling */
        struct bfq_entity *parent;

        /*
         * For non-leaf nodes in the hierarchy, the associated
         * scheduler queue, %NULL on leaf nodes.
         */
        struct bfq_sched_data *my_sched_data;
        /* the scheduler queue this entity belongs to */
        struct bfq_sched_data *sched_data;

        /* flag, set to request a weight, ioprio or ioprio_class change  */
        int prio_changed;
};

struct bfq_group;

/**
 * struct bfq_ttime - per process thinktime stats.
 */
struct bfq_ttime {
        /* completion time of the last request */
        u64 last_end_request;

        /* total process thinktime */
        u64 ttime_total;
        /* number of thinktime samples */
        unsigned long ttime_samples;
        /* average process thinktime */
        u64 ttime_mean;
};

/**
 * struct bfq_queue - leaf schedulable entity.
 *
 * A bfq_queue is a leaf request queue; it can be associated with an
 * io_context or more, if it is async. @cgroup holds a reference to
 * the cgroup, to be sure that it does not disappear while a bfqq
 * still references it (mostly to avoid races between request issuing
 * and task migration followed by cgroup destruction).  All the fields
 * are protected by the queue lock of the containing bfqd.
 */
struct bfq_queue {
        /* reference counter */
        int ref;
        /* parent bfq_data */
        struct bfq_data *bfqd;

        /* current ioprio and ioprio class */
        unsigned short ioprio, ioprio_class;
        /* next ioprio and ioprio class if a change is in progress */
        unsigned short new_ioprio, new_ioprio_class;

        /* sorted list of pending requests */
        struct rb_root sort_list;
        /* if fifo isn't expired, next request to serve */
        struct request *next_rq;
        /* number of sync and async requests queued */
        int queued[2];
        /* number of requests currently allocated */
        int allocated;
        /* number of pending metadata requests */
        int meta_pending;
        /* fifo list of requests in sort_list */
        struct list_head fifo;

        /* entity representing this queue in the scheduler */
        struct bfq_entity entity;

        /* maximum budget allowed from the feedback mechanism */
        int max_budget;
        /* budget expiration (in jiffies) */
        unsigned long budget_timeout;

        /* number of requests on the dispatch list or inside driver */
        int dispatched;

        /* status flags */
        unsigned long flags;

        /* node for active/idle bfqq list inside parent bfqd */
        struct list_head bfqq_list;

        /* associated @bfq_ttime struct */
        struct bfq_ttime ttime;

        /* bit vector: a 1 for each seeky requests in history */
        u32 seek_history;
        /* position of the last request enqueued */
        sector_t last_request_pos;

        /* Number of consecutive pairs of request completion and
         * arrival, such that the queue becomes idle after the
         * completion, but the next request arrives within an idle
         * time slice; used only if the queue's IO_bound flag has been
         * cleared.
         */
        unsigned int requests_within_timer;

        /* pid of the process owning the queue, used for logging purposes */
        pid_t pid;
};

/**
 * struct bfq_io_cq - per (request_queue, io_context) structure.
 */
struct bfq_io_cq {
        /* associated io_cq structure */
        struct io_cq icq; /* must be the first member */
        /* array of two process queues, the sync and the async */
        struct bfq_queue *bfqq[2];
        /* per (request_queue, blkcg) ioprio */
        int ioprio;
#ifdef CONFIG_BFQ_GROUP_IOSCHED
        uint64_t blkcg_serial_nr; /* the current blkcg serial */
#endif
};

/**
 * struct bfq_data - per-device data structure.
 *
 * All the fields are protected by @lock.
 */
struct bfq_data {
        /* device request queue */
        struct request_queue *queue;
        /* dispatch queue */
        struct list_head dispatch;

        /* root bfq_group for the device */
        struct bfq_group *root_group;

        /*
         * Number of bfq_queues containing requests (including the
         * queue in service, even if it is idling).
         */
        int busy_queues;
        /* number of queued requests */
        int queued;
        /* number of requests dispatched and waiting for completion */
        int rq_in_driver;

        /*
         * Maximum number of requests in driver in the last
         * @hw_tag_samples completed requests.
         */
        int max_rq_in_driver;
        /* number of samples used to calculate hw_tag */
        int hw_tag_samples;
        /* flag set to one if the driver is showing a queueing behavior */
        int hw_tag;

        /* number of budgets assigned */
        int budgets_assigned;

        /*
         * Timer set when idling (waiting) for the next request from
         * the queue in service.
         */
        struct hrtimer idle_slice_timer;

        /* bfq_queue in service */
        struct bfq_queue *in_service_queue;
        /* bfq_io_cq (bic) associated with the @in_service_queue */
        struct bfq_io_cq *in_service_bic;

        /* on-disk position of the last served request */
        sector_t last_position;

        /* time of last request completion (ns) */
        u64 last_completion;

        /* time of first rq dispatch in current observation interval (ns) */
        u64 first_dispatch;
        /* time of last rq dispatch in current observation interval (ns) */
        u64 last_dispatch;

        /* beginning of the last budget */
        ktime_t last_budget_start;
        /* beginning of the last idle slice */
        ktime_t last_idling_start;

        /* number of samples in current observation interval */
        int peak_rate_samples;
        /* num of samples of seq dispatches in current observation interval */
        u32 sequential_samples;
        /* total num of sectors transferred in current observation interval */
        u64 tot_sectors_dispatched;
        /* max rq size seen during current observation interval (sectors) */
        u32 last_rq_max_size;
        /* time elapsed from first dispatch in current observ. interval (us) */
        u64 delta_from_first;
        /*
         * Current estimate of the device peak rate, measured in
         * [BFQ_RATE_SHIFT * sectors/usec]. The left-shift by
         * BFQ_RATE_SHIFT is performed to increase precision in
         * fixed-point calculations.
         */
        u32 peak_rate;

        /* maximum budget allotted to a bfq_queue before rescheduling */
        int bfq_max_budget;

        /* list of all the bfq_queues active on the device */
        struct list_head active_list;
        /* list of all the bfq_queues idle on the device */
        struct list_head idle_list;

        /*
         * Timeout for async/sync requests; when it fires, requests
         * are served in fifo order.
         */
        u64 bfq_fifo_expire[2];
        /* weight of backward seeks wrt forward ones */
        unsigned int bfq_back_penalty;
        /* maximum allowed backward seek */
        unsigned int bfq_back_max;
        /* maximum idling time */
        u32 bfq_slice_idle;

        /* user-configured max budget value (0 for auto-tuning) */
        int bfq_user_max_budget;
        /*
         * Timeout for bfq_queues to consume their budget; used to
         * prevent seeky queues from imposing long latencies to
         * sequential or quasi-sequential ones (this also implies that
         * seeky queues cannot receive guarantees in the service
         * domain; after a timeout they are charged for the time they
         * have been in service, to preserve fairness among them, but
         * without service-domain guarantees).
         */
        unsigned int bfq_timeout;

        /*
         * Number of consecutive requests that must be issued within
         * the idle time slice to set again idling to a queue which
         * was marked as non-I/O-bound (see the definition of the
         * IO_bound flag for further details).
         */
        unsigned int bfq_requests_within_timer;

        /*
         * Force device idling whenever needed to provide accurate
         * service guarantees, without caring about throughput
         * issues. CAVEAT: this may even increase latencies, in case
         * of useless idling for processes that did stop doing I/O.
         */
        bool strict_guarantees;

        /* fallback dummy bfqq for extreme OOM conditions */
        struct bfq_queue oom_bfqq;

        spinlock_t lock;

        /*
         * bic associated with the task issuing current bio for
         * merging. This and the next field are used as a support to
         * be able to perform the bic lookup, needed by bio-merge
         * functions, before the scheduler lock is taken, and thus
         * avoid taking the request-queue lock while the scheduler
         * lock is being held.
         */
        struct bfq_io_cq *bio_bic;
        /* bfqq associated with the task issuing current bio for merging */
        struct bfq_queue *bio_bfqq;
};

enum bfqq_state_flags {
        BFQQF_busy = 0,         /* has requests or is in service */
        BFQQF_wait_request,     /* waiting for a request */
        BFQQF_non_blocking_wait_rq, /*
                                     * waiting for a request
                                     * without idling the device
                                     */
        BFQQF_fifo_expire,      /* FIFO checked in this slice */
        BFQQF_idle_window,      /* slice idling enabled */
        BFQQF_sync,             /* synchronous queue */
        BFQQF_budget_new,       /* no completion with this budget */
        BFQQF_IO_bound,         /*
                                 * bfqq has timed-out at least once
                                 * having consumed at most 2/10 of
                                 * its budget
                                 */
};

#define BFQ_BFQQ_FNS(name)                                              \
static void bfq_mark_bfqq_##name(struct bfq_queue *bfqq)                \
{                                                                       \
        __set_bit(BFQQF_##name, &(bfqq)->flags);                        \
}                                                                       \
static void bfq_clear_bfqq_##name(struct bfq_queue *bfqq)               \
{                                                                       \
        __clear_bit(BFQQF_##name, &(bfqq)->flags);              \
}                                                                       \
static int bfq_bfqq_##name(const struct bfq_queue *bfqq)                \
{                                                                       \
        return test_bit(BFQQF_##name, &(bfqq)->flags);          \
}

BFQ_BFQQ_FNS(busy);
BFQ_BFQQ_FNS(wait_request);
BFQ_BFQQ_FNS(non_blocking_wait_rq);
BFQ_BFQQ_FNS(fifo_expire);
BFQ_BFQQ_FNS(idle_window);
BFQ_BFQQ_FNS(sync);
BFQ_BFQQ_FNS(budget_new);
BFQ_BFQQ_FNS(IO_bound);
#undef BFQ_BFQQ_FNS

/* Logging facilities. */
#ifdef CONFIG_BFQ_GROUP_IOSCHED
static struct bfq_group *bfqq_group(struct bfq_queue *bfqq);
static struct blkcg_gq *bfqg_to_blkg(struct bfq_group *bfqg);

#define bfq_log_bfqq(bfqd, bfqq, fmt, args...)  do {                    \
        char __pbuf[128];                                               \
                                                                        \
        blkg_path(bfqg_to_blkg(bfqq_group(bfqq)), __pbuf, sizeof(__pbuf)); \
        blk_add_trace_msg((bfqd)->queue, "bfq%d%c %s " fmt, (bfqq)->pid, \
                        bfq_bfqq_sync((bfqq)) ? 'S' : 'A',              \
                          __pbuf, ##args);                              \
} while (0)

#define bfq_log_bfqg(bfqd, bfqg, fmt, args...)  do {                    \
        char __pbuf[128];                                               \
                                                                        \
        blkg_path(bfqg_to_blkg(bfqg), __pbuf, sizeof(__pbuf));          \
        blk_add_trace_msg((bfqd)->queue, "%s " fmt, __pbuf, ##args);    \
} while (0)

#else /* CONFIG_BFQ_GROUP_IOSCHED */

#define bfq_log_bfqq(bfqd, bfqq, fmt, args...)  \
        blk_add_trace_msg((bfqd)->queue, "bfq%d%c " fmt, (bfqq)->pid,   \
                        bfq_bfqq_sync((bfqq)) ? 'S' : 'A',              \
                                ##args)
#define bfq_log_bfqg(bfqd, bfqg, fmt, args...)          do {} while (0)

#endif /* CONFIG_BFQ_GROUP_IOSCHED */

#define bfq_log(bfqd, fmt, args...) \
        blk_add_trace_msg((bfqd)->queue, "bfq " fmt, ##args)

/* Expiration reasons. */
enum bfqq_expiration {
        BFQQE_TOO_IDLE = 0,             /*
                                         * queue has been idling for
                                         * too long
                                         */
        BFQQE_BUDGET_TIMEOUT,   /* budget took too long to be used */
        BFQQE_BUDGET_EXHAUSTED, /* budget consumed */
        BFQQE_NO_MORE_REQUESTS, /* the queue has no more requests */
        BFQQE_PREEMPTED         /* preemption in progress */
};

struct bfqg_stats {
#ifdef CONFIG_BFQ_GROUP_IOSCHED
        /* number of ios merged */
        struct blkg_rwstat              merged;
        /* total time spent on device in ns, may not be accurate w/ queueing */
        struct blkg_rwstat              service_time;
        /* total time spent waiting in scheduler queue in ns */
        struct blkg_rwstat              wait_time;
        /* number of IOs queued up */
        struct blkg_rwstat              queued;
        /* total disk time and nr sectors dispatched by this group */
        struct blkg_stat                time;
        /* sum of number of ios queued across all samples */
        struct blkg_stat                avg_queue_size_sum;
        /* count of samples taken for average */
        struct blkg_stat                avg_queue_size_samples;
        /* how many times this group has been removed from service tree */
        struct blkg_stat                dequeue;
        /* total time spent waiting for it to be assigned a timeslice. */
        struct blkg_stat                group_wait_time;
        /* time spent idling for this blkcg_gq */
        struct blkg_stat                idle_time;
        /* total time with empty current active q with other requests queued */
        struct blkg_stat                empty_time;
        /* fields after this shouldn't be cleared on stat reset */
        uint64_t                        start_group_wait_time;
        uint64_t                        start_idle_time;
        uint64_t                        start_empty_time;
        uint16_t                        flags;
#endif  /* CONFIG_BFQ_GROUP_IOSCHED */
};

#ifdef CONFIG_BFQ_GROUP_IOSCHED

/*
 * struct bfq_group_data - per-blkcg storage for the blkio subsystem.
 *
 * @ps: @blkcg_policy_storage that this structure inherits
 * @weight: weight of the bfq_group
 */
struct bfq_group_data {
        /* must be the first member */
        struct blkcg_policy_data pd;

        unsigned short weight;
};

/**
 * struct bfq_group - per (device, cgroup) data structure.
 * @entity: schedulable entity to insert into the parent group sched_data.
 * @sched_data: own sched_data, to contain child entities (they may be
 *              both bfq_queues and bfq_groups).
 * @bfqd: the bfq_data for the device this group acts upon.
 * @async_bfqq: array of async queues for all the tasks belonging to
 *              the group, one queue per ioprio value per ioprio_class,
 *              except for the idle class that has only one queue.
 * @async_idle_bfqq: async queue for the idle class (ioprio is ignored).
 * @my_entity: pointer to @entity, %NULL for the toplevel group; used
 *             to avoid too many special cases during group creation/
 *             migration.
 * @stats: stats for this bfqg.
 *
 * Each (device, cgroup) pair has its own bfq_group, i.e., for each cgroup
 * there is a set of bfq_groups, each one collecting the lower-level
 * entities belonging to the group that are acting on the same device.
 *
 * Locking works as follows:
 *    o @bfqd is protected by the queue lock, RCU is used to access it
 *      from the readers.
 *    o All the other fields are protected by the @bfqd queue lock.
 */
struct bfq_group {
        /* must be the first member */
        struct blkg_policy_data pd;

        struct bfq_entity entity;
        struct bfq_sched_data sched_data;

        void *bfqd;

        struct bfq_queue *async_bfqq[2][IOPRIO_BE_NR];
        struct bfq_queue *async_idle_bfqq;

        struct bfq_entity *my_entity;

        struct bfqg_stats stats;
};

#else
struct bfq_group {
        struct bfq_sched_data sched_data;

        struct bfq_queue *async_bfqq[2][IOPRIO_BE_NR];
        struct bfq_queue *async_idle_bfqq;

        struct rb_root rq_pos_tree;
};
#endif

static struct bfq_queue *bfq_entity_to_bfqq(struct bfq_entity *entity);

static unsigned int bfq_class_idx(struct bfq_entity *entity)
{
        struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);

        return bfqq ? bfqq->ioprio_class - 1 :
                BFQ_DEFAULT_GRP_CLASS - 1;
}

static struct bfq_service_tree *
bfq_entity_service_tree(struct bfq_entity *entity)
{
        struct bfq_sched_data *sched_data = entity->sched_data;
        unsigned int idx = bfq_class_idx(entity);

        return sched_data->service_tree + idx;
}

static struct bfq_queue *bic_to_bfqq(struct bfq_io_cq *bic, bool is_sync)
{
        return bic->bfqq[is_sync];
}

static void bic_set_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq,
                         bool is_sync)
{
        bic->bfqq[is_sync] = bfqq;
}

static struct bfq_data *bic_to_bfqd(struct bfq_io_cq *bic)
{
        return bic->icq.q->elevator->elevator_data;
}

static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio);
static void bfq_put_queue(struct bfq_queue *bfqq);
static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
                                       struct bio *bio, bool is_sync,
                                       struct bfq_io_cq *bic);
static void bfq_put_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg);
static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq);

/* Expiration time of sync (0) and async (1) requests, in ns. */
static const u64 bfq_fifo_expire[2] = { NSEC_PER_SEC / 4, NSEC_PER_SEC / 8 };

/* Maximum backwards seek (magic number lifted from CFQ), in KiB. */
static const int bfq_back_max = 16 * 1024;

/* Penalty of a backwards seek, in number of sectors. */
static const int bfq_back_penalty = 2;

/* Idling period duration, in ns. */
static u64 bfq_slice_idle = NSEC_PER_SEC / 125;

/* Minimum number of assigned budgets for which stats are safe to compute. */
static const int bfq_stats_min_budgets = 194;

/* Default maximum budget values, in sectors and number of requests. */
static const int bfq_default_max_budget = 16 * 1024;

/*
 * Async to sync throughput distribution is controlled as follows:
 * when an async request is served, the entity is charged the number
 * of sectors of the request, multiplied by the factor below
 */
static const int bfq_async_charge_factor = 10;

/* Default timeout values, in jiffies, approximating CFQ defaults. */
static const int bfq_timeout = HZ / 8;

static struct kmem_cache *bfq_pool;

/* Below this threshold (in ns), we consider thinktime immediate. */
#define BFQ_MIN_TT              (2 * NSEC_PER_MSEC)

/* hw_tag detection: parallel requests threshold and min samples needed. */
#define BFQ_HW_QUEUE_THRESHOLD  4
#define BFQ_HW_QUEUE_SAMPLES    32

#define BFQQ_SEEK_THR           (sector_t)(8 * 100)
#define BFQQ_SECT_THR_NONROT    (sector_t)(2 * 32)
#define BFQQ_CLOSE_THR          (sector_t)(8 * 1024)
#define BFQQ_SEEKY(bfqq)        (hweight32(bfqq->seek_history) > 32/8)

/* Min number of samples required to perform peak-rate update */
#define BFQ_RATE_MIN_SAMPLES    32
/* Min observation time interval required to perform a peak-rate update (ns) */
#define BFQ_RATE_MIN_INTERVAL   (300*NSEC_PER_MSEC)
/* Target observation time interval for a peak-rate update (ns) */
#define BFQ_RATE_REF_INTERVAL   NSEC_PER_SEC

/* Shift used for peak rate fixed precision calculations. */
#define BFQ_RATE_SHIFT          16

#define BFQ_SERVICE_TREE_INIT   ((struct bfq_service_tree)              \
                                { RB_ROOT, RB_ROOT, NULL, NULL, 0, 0 })

#define RQ_BIC(rq)              ((struct bfq_io_cq *) (rq)->elv.priv[0])
#define RQ_BFQQ(rq)             ((rq)->elv.priv[1])

/**
 * icq_to_bic - convert iocontext queue structure to bfq_io_cq.
 * @icq: the iocontext queue.
 */
static struct bfq_io_cq *icq_to_bic(struct io_cq *icq)
{
        /* bic->icq is the first member, %NULL will convert to %NULL */
        return container_of(icq, struct bfq_io_cq, icq);
}

/**
 * bfq_bic_lookup - search into @ioc a bic associated to @bfqd.
 * @bfqd: the lookup key.
 * @ioc: the io_context of the process doing I/O.
 * @q: the request queue.
 */
static struct bfq_io_cq *bfq_bic_lookup(struct bfq_data *bfqd,
                                        struct io_context *ioc,
                                        struct request_queue *q)
{
        if (ioc) {
                unsigned long flags;
                struct bfq_io_cq *icq;

                spin_lock_irqsave(q->queue_lock, flags);
                icq = icq_to_bic(ioc_lookup_icq(ioc, q));
                spin_unlock_irqrestore(q->queue_lock, flags);

                return icq;
        }

        return NULL;
}

/*
 * Scheduler run of queue, if there are requests pending and no one in the
 * driver that will restart queueing.
 */
static void bfq_schedule_dispatch(struct bfq_data *bfqd)
{
        if (bfqd->queued != 0) {
                bfq_log(bfqd, "schedule dispatch");
                blk_mq_run_hw_queues(bfqd->queue, true);
        }
}

/**
 * bfq_gt - compare two timestamps.
 * @a: first ts.
 * @b: second ts.
 *
 * Return @a > @b, dealing with wrapping correctly.
 */
static int bfq_gt(u64 a, u64 b)
{
        return (s64)(a - b) > 0;
}

static struct bfq_entity *bfq_root_active_entity(struct rb_root *tree)
{
        struct rb_node *node = tree->rb_node;

        return rb_entry(node, struct bfq_entity, rb_node);
}

static struct bfq_entity *bfq_lookup_next_entity(struct bfq_sched_data *sd);

static bool bfq_update_parent_budget(struct bfq_entity *next_in_service);

/**
 * bfq_update_next_in_service - update sd->next_in_service
 * @sd: sched_data for which to perform the update.
 * @new_entity: if not NULL, pointer to the entity whose activation,
 *              requeueing or repositionig triggered the invocation of
 *              this function.
 *
 * This function is called to update sd->next_in_service, which, in
 * its turn, may change as a consequence of the insertion or
 * extraction of an entity into/from one of the active trees of
 * sd. These insertions/extractions occur as a consequence of
 * activations/deactivations of entities, with some activations being
 * 'true' activations, and other activations being requeueings (i.e.,
 * implementing the second, requeueing phase of the mechanism used to
 * reposition an entity in its active tree; see comments on
 * __bfq_activate_entity and __bfq_requeue_entity for details). In
 * both the last two activation sub-cases, new_entity points to the
 * just activated or requeued entity.
 *
 * Returns true if sd->next_in_service changes in such a way that
 * entity->parent may become the next_in_service for its parent
 * entity.
 */
static bool bfq_update_next_in_service(struct bfq_sched_data *sd,
                                       struct bfq_entity *new_entity)
{
        struct bfq_entity *next_in_service = sd->next_in_service;
        bool parent_sched_may_change = false;

        /*
         * If this update is triggered by the activation, requeueing
         * or repositiong of an entity that does not coincide with
         * sd->next_in_service, then a full lookup in the active tree
         * can be avoided. In fact, it is enough to check whether the
         * just-modified entity has a higher priority than
         * sd->next_in_service, or, even if it has the same priority
         * as sd->next_in_service, is eligible and has a lower virtual
         * finish time than sd->next_in_service. If this compound
         * condition holds, then the new entity becomes the new
         * next_in_service. Otherwise no change is needed.
         */
        if (new_entity && new_entity != sd->next_in_service) {
                /*
                 * Flag used to decide whether to replace
                 * sd->next_in_service with new_entity. Tentatively
                 * set to true, and left as true if
                 * sd->next_in_service is NULL.
                 */
                bool replace_next = true;

                /*
                 * If there is already a next_in_service candidate
                 * entity, then compare class priorities or timestamps
                 * to decide whether to replace sd->service_tree with
                 * new_entity.
                 */
                if (next_in_service) {
                        unsigned int new_entity_class_idx =
                                bfq_class_idx(new_entity);
                        struct bfq_service_tree *st =
                                sd->service_tree + new_entity_class_idx;

                        /*
                         * For efficiency, evaluate the most likely
                         * sub-condition first.
                         */
                        replace_next =
                                (new_entity_class_idx ==
                                 bfq_class_idx(next_in_service)
                                 &&
                                 !bfq_gt(new_entity->start, st->vtime)
                                 &&
                                 bfq_gt(next_in_service->finish,
                                        new_entity->finish))
                                ||
                                new_entity_class_idx <
                                bfq_class_idx(next_in_service);
                }

                if (replace_next)
                        next_in_service = new_entity;
        } else /* invoked because of a deactivation: lookup needed */
                next_in_service = bfq_lookup_next_entity(sd);

        if (next_in_service) {
                parent_sched_may_change = !sd->next_in_service ||
                        bfq_update_parent_budget(next_in_service);
        }

        sd->next_in_service = next_in_service;

        if (!next_in_service)
                return parent_sched_may_change;

        return parent_sched_may_change;
}

#ifdef CONFIG_BFQ_GROUP_IOSCHED
/* both next loops stop at one of the child entities of the root group */
#define for_each_entity(entity) \
        for (; entity ; entity = entity->parent)

/*
 * For each iteration, compute parent in advance, so as to be safe if
 * entity is deallocated during the iteration. Such a deallocation may
 * happen as a consequence of a bfq_put_queue that frees the bfq_queue
 * containing entity.
 */
#define for_each_entity_safe(entity, parent) \
        for (; entity && ({ parent = entity->parent; 1; }); entity = parent)

/*
 * Returns true if this budget changes may let next_in_service->parent
 * become the next_in_service entity for its parent entity.
 */
static bool bfq_update_parent_budget(struct bfq_entity *next_in_service)
{
        struct bfq_entity *bfqg_entity;
        struct bfq_group *bfqg;
        struct bfq_sched_data *group_sd;
        bool ret = false;

        group_sd = next_in_service->sched_data;

        bfqg = container_of(group_sd, struct bfq_group, sched_data);
        /*
         * bfq_group's my_entity field is not NULL only if the group
         * is not the root group. We must not touch the root entity
         * as it must never become an in-service entity.
         */
        bfqg_entity = bfqg->my_entity;
        if (bfqg_entity) {
                if (bfqg_entity->budget > next_in_service->budget)
                        ret = true;
                bfqg_entity->budget = next_in_service->budget;
        }

        return ret;
}

/*
 * This function tells whether entity stops being a candidate for next
 * service, according to the following logic.
 *
 * This function is invoked for an entity that is about to be set in
 * service. If such an entity is a queue, then the entity is no longer
 * a candidate for next service (i.e, a candidate entity to serve
 * after the in-service entity is expired). The function then returns
 * true.
 */
static bool bfq_no_longer_next_in_service(struct bfq_entity *entity)
{
        if (bfq_entity_to_bfqq(entity))
                return true;

        return false;
}

#else /* CONFIG_BFQ_GROUP_IOSCHED */
/*
 * Next two macros are fake loops when cgroups support is not
 * enabled. I fact, in such a case, there is only one level to go up
 * (to reach the root group).
 */
#define for_each_entity(entity) \
        for (; entity ; entity = NULL)

#define for_each_entity_safe(entity, parent) \
        for (parent = NULL; entity ; entity = parent)

static bool bfq_update_parent_budget(struct bfq_entity *next_in_service)
{
        return false;
}

static bool bfq_no_longer_next_in_service(struct bfq_entity *entity)
{
        return true;
}

#endif /* CONFIG_BFQ_GROUP_IOSCHED */

/*
 * Shift for timestamp calculations.  This actually limits the maximum
 * service allowed in one timestamp delta (small shift values increase it),
 * the maximum total weight that can be used for the queues in the system
 * (big shift values increase it), and the period of virtual time
 * wraparounds.
 */
#define WFQ_SERVICE_SHIFT       22

static struct bfq_queue *bfq_entity_to_bfqq(struct bfq_entity *entity)
{
        struct bfq_queue *bfqq = NULL;

        if (!entity->my_sched_data)
                bfqq = container_of(entity, struct bfq_queue, entity);

        return bfqq;
}


/**
 * bfq_delta - map service into the virtual time domain.
 * @service: amount of service.
 * @weight: scale factor (weight of an entity or weight sum).
 */
static u64 bfq_delta(unsigned long service, unsigned long weight)
{
        u64 d = (u64)service << WFQ_SERVICE_SHIFT;

        do_div(d, weight);
        return d;
}

/**
 * bfq_calc_finish - assign the finish time to an entity.
 * @entity: the entity to act upon.
 * @service: the service to be charged to the entity.
 */
static void bfq_calc_finish(struct bfq_entity *entity, unsigned long service)
{
        struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);

        entity->finish = entity->start +
                bfq_delta(service, entity->weight);

        if (bfqq) {
                bfq_log_bfqq(bfqq->bfqd, bfqq,
                        "calc_finish: serv %lu, w %d",
                        service, entity->weight);
                bfq_log_bfqq(bfqq->bfqd, bfqq,
                        "calc_finish: start %llu, finish %llu, delta %llu",
                        entity->start, entity->finish,
                        bfq_delta(service, entity->weight));
        }
}

/**
 * bfq_entity_of - get an entity from a node.
 * @node: the node field of the entity.
 *
 * Convert a node pointer to the relative entity.  This is used only
 * to simplify the logic of some functions and not as the generic
 * conversion mechanism because, e.g., in the tree walking functions,
 * the check for a %NULL value would be redundant.
 */
static struct bfq_entity *bfq_entity_of(struct rb_node *node)
{
        struct bfq_entity *entity = NULL;

        if (node)
                entity = rb_entry(node, struct bfq_entity, rb_node);

        return entity;
}

/**
 * bfq_extract - remove an entity from a tree.
 * @root: the tree root.
 * @entity: the entity to remove.
 */
static void bfq_extract(struct rb_root *root, struct bfq_entity *entity)
{
        entity->tree = NULL;
        rb_erase(&entity->rb_node, root);
}

/**
 * bfq_idle_extract - extract an entity from the idle tree.
 * @st: the service tree of the owning @entity.
 * @entity: the entity being removed.
 */
static void bfq_idle_extract(struct bfq_service_tree *st,
                             struct bfq_entity *entity)
{
        struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
        struct rb_node *next;

        if (entity == st->first_idle) {
                next = rb_next(&entity->rb_node);
                st->first_idle = bfq_entity_of(next);
        }

        if (entity == st->last_idle) {
                next = rb_prev(&entity->rb_node);
                st->last_idle = bfq_entity_of(next);
        }

        bfq_extract(&st->idle, entity);

        if (bfqq)
                list_del(&bfqq->bfqq_list);
}

/**
 * bfq_insert - generic tree insertion.
 * @root: tree root.
 * @entity: entity to insert.
 *
 * This is used for the idle and the active tree, since they are both
 * ordered by finish time.
 */
static void bfq_insert(struct rb_root *root, struct bfq_entity *entity)
{
        struct bfq_entity *entry;
        struct rb_node **node = &root->rb_node;
        struct rb_node *parent = NULL;

        while (*node) {
                parent = *node;
                entry = rb_entry(parent, struct bfq_entity, rb_node);

                if (bfq_gt(entry->finish, entity->finish))
                        node = &parent->rb_left;
                else
                        node = &parent->rb_right;
        }

        rb_link_node(&entity->rb_node, parent, node);
        rb_insert_color(&entity->rb_node, root);

        entity->tree = root;
}

/**
 * bfq_update_min - update the min_start field of a entity.
 * @entity: the entity to update.
 * @node: one of its children.
 *
 * This function is called when @entity may store an invalid value for
 * min_start due to updates to the active tree.  The function  assumes
 * that the subtree rooted at @node (which may be its left or its right
 * child) has a valid min_start value.
 */
static void bfq_update_min(struct bfq_entity *entity, struct rb_node *node)
{
        struct bfq_entity *child;

        if (node) {
                child = rb_entry(node, struct bfq_entity, rb_node);
                if (bfq_gt(entity->min_start, child->min_start))
                        entity->min_start = child->min_start;
        }
}

/**
 * bfq_update_active_node - recalculate min_start.
 * @node: the node to update.
 *
 * @node may have changed position or one of its children may have moved,
 * this function updates its min_start value.  The left and right subtrees
 * are assumed to hold a correct min_start value.
 */
static void bfq_update_active_node(struct rb_node *node)
{
        struct bfq_entity *entity = rb_entry(node, struct bfq_entity, rb_node);

        entity->min_start = entity->start;
        bfq_update_min(entity, node->rb_right);
        bfq_update_min(entity, node->rb_left);
}

/**
 * bfq_update_active_tree - update min_start for the whole active tree.
 * @node: the starting node.
 *
 * @node must be the deepest modified node after an update.  This function
 * updates its min_start using the values held by its children, assuming
 * that they did not change, and then updates all the nodes that may have
 * changed in the path to the root.  The only nodes that may have changed
 * are the ones in the path or their siblings.
 */
static void bfq_update_active_tree(struct rb_node *node)
{
        struct rb_node *parent;

up:
        bfq_update_active_node(node);

        parent = rb_parent(node);
        if (!parent)
                return;

        if (node == parent->rb_left && parent->rb_right)
                bfq_update_active_node(parent->rb_right);
        else if (parent->rb_left)
                bfq_update_active_node(parent->rb_left);

        node = parent;
        goto up;
}

/**
 * bfq_active_insert - insert an entity in the active tree of its
 *                     group/device.
 * @st: the service tree of the entity.
 * @entity: the entity being inserted.
 *
 * The active tree is ordered by finish time, but an extra key is kept
 * per each node, containing the minimum value for the start times of
 * its children (and the node itself), so it's possible to search for
 * the eligible node with the lowest finish time in logarithmic time.
 */
static void bfq_active_insert(struct bfq_service_tree *st,
                              struct bfq_entity *entity)
{
        struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
        struct rb_node *node = &entity->rb_node;
#ifdef CONFIG_BFQ_GROUP_IOSCHED
        struct bfq_sched_data *sd = NULL;
        struct bfq_group *bfqg = NULL;
        struct bfq_data *bfqd = NULL;
#endif

        bfq_insert(&st->active, entity);

        if (node->rb_left)
                node = node->rb_left;
        else if (node->rb_right)
                node = node->rb_right;

        bfq_update_active_tree(node);

#ifdef CONFIG_BFQ_GROUP_IOSCHED
        sd = entity->sched_data;
        bfqg = container_of(sd, struct bfq_group, sched_data);
        bfqd = (struct bfq_data *)bfqg->bfqd;
#endif
        if (bfqq)
                list_add(&bfqq->bfqq_list, &bfqq->bfqd->active_list);
}

/**
 * bfq_ioprio_to_weight - calc a weight from an ioprio.
 * @ioprio: the ioprio value to convert.
 */
static unsigned short bfq_ioprio_to_weight(int ioprio)
{
        return (IOPRIO_BE_NR - ioprio) * BFQ_WEIGHT_CONVERSION_COEFF;
}

/**
 * bfq_weight_to_ioprio - calc an ioprio from a weight.
 * @weight: the weight value to convert.
 *
 * To preserve as much as possible the old only-ioprio user interface,
 * 0 is used as an escape ioprio value for weights (numerically) equal or
 * larger than IOPRIO_BE_NR * BFQ_WEIGHT_CONVERSION_COEFF.
 */
static unsigned short bfq_weight_to_ioprio(int weight)
{
        return max_t(int, 0,
                     IOPRIO_BE_NR * BFQ_WEIGHT_CONVERSION_COEFF - weight);
}

static void bfq_get_entity(struct bfq_entity *entity)
{
        struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);

        if (bfqq) {
                bfqq->ref++;
                bfq_log_bfqq(bfqq->bfqd, bfqq, "get_entity: %p %d",
                             bfqq, bfqq->ref);
        }
}

/**
 * bfq_find_deepest - find the deepest node that an extraction can modify.
 * @node: the node being removed.
 *
 * Do the first step of an extraction in an rb tree, looking for the
 * node that will replace @node, and returning the deepest node that
 * the following modifications to the tree can touch.  If @node is the
 * last node in the tree return %NULL.
 */
static struct rb_node *bfq_find_deepest(struct rb_node *node)
{
        struct rb_node *deepest;

        if (!node->rb_right && !node->rb_left)
                deepest = rb_parent(node);
        else if (!node->rb_right)
                deepest = node->rb_left;
        else if (!node->rb_left)
                deepest = node->rb_right;
        else {
                deepest = rb_next(node);
                if (deepest->rb_right)
                        deepest = deepest->rb_right;
                else if (rb_parent(deepest) != node)
                        deepest = rb_parent(deepest);
        }

        return deepest;
}

/**
 * bfq_active_extract - remove an entity from the active tree.
 * @st: the service_tree containing the tree.
 * @entity: the entity being removed.
 */
static void bfq_active_extract(struct bfq_service_tree *st,
                               struct bfq_entity *entity)
{
        struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
        struct rb_node *node;
#ifdef CONFIG_BFQ_GROUP_IOSCHED
        struct bfq_sched_data *sd = NULL;
        struct bfq_group *bfqg = NULL;
        struct bfq_data *bfqd = NULL;
#endif

        node = bfq_find_deepest(&entity->rb_node);
        bfq_extract(&st->active, entity);

        if (node)
                bfq_update_active_tree(node);

#ifdef CONFIG_BFQ_GROUP_IOSCHED
        sd = entity->sched_data;
        bfqg = container_of(sd, struct bfq_group, sched_data);
        bfqd = (struct bfq_data *)bfqg->bfqd;
#endif
        if (bfqq)
                list_del(&bfqq->bfqq_list);
}

/**
 * bfq_idle_insert - insert an entity into the idle tree.
 * @st: the service tree containing the tree.
 * @entity: the entity to insert.
 */
static void bfq_idle_insert(struct bfq_service_tree *st,
                            struct bfq_entity *entity)
{
        struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
        struct bfq_entity *first_idle = st->first_idle;
        struct bfq_entity *last_idle = st->last_idle;

        if (!first_idle || bfq_gt(first_idle->finish, entity->finish))
                st->first_idle = entity;
        if (!last_idle || bfq_gt(entity->finish, last_idle->finish))
                st->last_idle = entity;

        bfq_insert(&st->idle, entity);

        if (bfqq)
                list_add(&bfqq->bfqq_list, &bfqq->bfqd->idle_list);
}

/**
 * bfq_forget_entity - do not consider entity any longer for scheduling
 * @st: the service tree.
 * @entity: the entity being removed.
 * @is_in_service: true if entity is currently the in-service entity.
 *
 * Forget everything about @entity. In addition, if entity represents
 * a queue, and the latter is not in service, then release the service
 * reference to the queue (the one taken through bfq_get_entity). In
 * fact, in this case, there is really no more service reference to
 * the queue, as the latter is also outside any service tree. If,
 * instead, the queue is in service, then __bfq_bfqd_reset_in_service
 * will take care of putting the reference when the queue finally
 * stops being served.
 */
static void bfq_forget_entity(struct bfq_service_tree *st,
                              struct bfq_entity *entity,
                              bool is_in_service)
{
        struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);

        entity->on_st = false;
        st->wsum -= entity->weight;
        if (bfqq && !is_in_service)
                bfq_put_queue(bfqq);
}

/**
 * bfq_put_idle_entity - release the idle tree ref of an entity.
 * @st: service tree for the entity.
 * @entity: the entity being released.
 */
static void bfq_put_idle_entity(struct bfq_service_tree *st,
                                struct bfq_entity *entity)
{
        bfq_idle_extract(st, entity);
        bfq_forget_entity(st, entity,
                          entity == entity->sched_data->in_service_entity);
}

/**
 * bfq_forget_idle - update the idle tree if necessary.
 * @st: the service tree to act upon.
 *
 * To preserve the global O(log N) complexity we only remove one entry here;
 * as the idle tree will not grow indefinitely this can be done safely.
 */
static void bfq_forget_idle(struct bfq_service_tree *st)
{
        struct bfq_entity *first_idle = st->first_idle;
        struct bfq_entity *last_idle = st->last_idle;

        if (RB_EMPTY_ROOT(&st->active) && last_idle &&
            !bfq_gt(last_idle->finish, st->vtime)) {
                /*
                 * Forget the whole idle tree, increasing the vtime past
                 * the last finish time of idle entities.
                 */
                st->vtime = last_idle->finish;
        }

        if (first_idle && !bfq_gt(first_idle->finish, st->vtime))
                bfq_put_idle_entity(st, first_idle);
}

static struct bfq_service_tree *
__bfq_entity_update_weight_prio(struct bfq_service_tree *old_st,
                                struct bfq_entity *entity)
{
        struct bfq_service_tree *new_st = old_st;

        if (entity->prio_changed) {
                struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
                unsigned short prev_weight, new_weight;
                struct bfq_data *bfqd = NULL;
#ifdef CONFIG_BFQ_GROUP_IOSCHED
                struct bfq_sched_data *sd;
                struct bfq_group *bfqg;
#endif

                if (bfqq)
                        bfqd = bfqq->bfqd;
#ifdef CONFIG_BFQ_GROUP_IOSCHED
                else {
                        sd = entity->my_sched_data;
                        bfqg = container_of(sd, struct bfq_group, sched_data);
                        bfqd = (struct bfq_data *)bfqg->bfqd;
                }
#endif

                old_st->wsum -= entity->weight;

                if (entity->new_weight != entity->orig_weight) {
                        if (entity->new_weight < BFQ_MIN_WEIGHT ||
                            entity->new_weight > BFQ_MAX_WEIGHT) {
                                pr_crit("update_weight_prio: new_weight %d\n",
                                        entity->new_weight);
                                if (entity->new_weight < BFQ_MIN_WEIGHT)
                                        entity->new_weight = BFQ_MIN_WEIGHT;
                                else
                                        entity->new_weight = BFQ_MAX_WEIGHT;
                        }
                        entity->orig_weight = entity->new_weight;
                        if (bfqq)
                                bfqq->ioprio =
                                  bfq_weight_to_ioprio(entity->orig_weight);
                }

                if (bfqq)
                        bfqq->ioprio_class = bfqq->new_ioprio_class;
                entity->prio_changed = 0;

                /*
                 * NOTE: here we may be changing the weight too early,
                 * this will cause unfairness.  The correct approach
                 * would have required additional complexity to defer
                 * weight changes to the proper time instants (i.e.,
                 * when entity->finish <= old_st->vtime).
                 */
                new_st = bfq_entity_service_tree(entity);

                prev_weight = entity->weight;
                new_weight = entity->orig_weight;
                entity->weight = new_weight;

                new_st->wsum += entity->weight;

                if (new_st != old_st)
                        entity->start = new_st->vtime;
        }

        return new_st;
}

static void bfqg_stats_set_start_empty_time(struct bfq_group *bfqg);
static struct bfq_group *bfqq_group(struct bfq_queue *bfqq);

/**
 * bfq_bfqq_served - update the scheduler status after selection for
 *                   service.
 * @bfqq: the queue being served.
 * @served: bytes to transfer.
 *
 * NOTE: this can be optimized, as the timestamps of upper level entities
 * are synchronized every time a new bfqq is selected for service.  By now,
 * we keep it to better check consistency.
 */
static void bfq_bfqq_served(struct bfq_queue *bfqq, int served)
{
        struct bfq_entity *entity = &bfqq->entity;
        struct bfq_service_tree *st;

        for_each_entity(entity) {
                st = bfq_entity_service_tree(entity);

                entity->service += served;

                st->vtime += bfq_delta(served, st->wsum);
                bfq_forget_idle(st);
        }
        bfqg_stats_set_start_empty_time(bfqq_group(bfqq));
        bfq_log_bfqq(bfqq->bfqd, bfqq, "bfqq_served %d secs", served);
}

/**
 * bfq_bfqq_charge_time - charge an amount of service equivalent to the length
 *                        of the time interval during which bfqq has been in
 *                        service.
 * @bfqd: the device
 * @bfqq: the queue that needs a service update.
 * @time_ms: the amount of time during which the queue has received service
 *
 * If a queue does not consume its budget fast enough, then providing
 * the queue with service fairness may impair throughput, more or less
 * severely. For this reason, queues that consume their budget slowly
 * are provided with time fairness instead of service fairness. This
 * goal is achieved through the BFQ scheduling engine, even if such an
 * engine works in the service, and not in the time domain. The trick
 * is charging these queues with an inflated amount of service, equal
 * to the amount of service that they would have received during their
 * service slot if they had been fast, i.e., if their requests had
 * been dispatched at a rate equal to the estimated peak rate.
 *
 * It is worth noting that time fairness can cause important
 * distortions in terms of bandwidth distribution, on devices with
 * internal queueing. The reason is that I/O requests dispatched
 * during the service slot of a queue may be served after that service
 * slot is finished, and may have a total processing time loosely
 * correlated with the duration of the service slot. This is
 * especially true for short service slots.
 */
static void bfq_bfqq_charge_time(struct bfq_data *bfqd, struct bfq_queue *bfqq,
                                 unsigned long time_ms)
{
        struct bfq_entity *entity = &bfqq->entity;
        int tot_serv_to_charge = entity->service;
        unsigned int timeout_ms = jiffies_to_msecs(bfq_timeout);

        if (time_ms > 0 && time_ms < timeout_ms)
                tot_serv_to_charge =
                        (bfqd->bfq_max_budget * time_ms) / timeout_ms;

        if (tot_serv_to_charge < entity->service)
                tot_serv_to_charge = entity->service;

        /* Increase budget to avoid inconsistencies */
        if (tot_serv_to_charge > entity->budget)
                entity->budget = tot_serv_to_charge;

        bfq_bfqq_served(bfqq,
                        max_t(int, 0, tot_serv_to_charge - entity->service));
}

static void bfq_update_fin_time_enqueue(struct bfq_entity *entity,
                                        struct bfq_service_tree *st,
                                        bool backshifted)
{
        st = __bfq_entity_update_weight_prio(st, entity);
        bfq_calc_finish(entity, entity->budget);

        /*
         * If some queues enjoy backshifting for a while, then their
         * (virtual) finish timestamps may happen to become lower and
         * lower than the system virtual time.  In particular, if
         * these queues often happen to be idle for short time
         * periods, and during such time periods other queues with
         * higher timestamps happen to be busy, then the backshifted
         * timestamps of the former queues can become much lower than
         * the system virtual time. In fact, to serve the queues with
         * higher timestamps while the ones with lower timestamps are
         * idle, the system virtual time may be pushed-up to much
         * higher values than the finish timestamps of the idle
         * queues. As a consequence, the finish timestamps of all new
         * or newly activated queues may end up being much larger than
         * those of lucky queues with backshifted timestamps. The
         * latter queues may then monopolize the device for a lot of
         * time. This would simply break service guarantees.
         *
         * To reduce this problem, push up a little bit the
         * backshifted timestamps of the queue associated with this
         * entity (only a queue can happen to have the backshifted
         * flag set): just enough to let the finish timestamp of the
         * queue be equal to the current value of the system virtual
         * time. This may introduce a little unfairness among queues
         * with backshifted timestamps, but it does not break
         * worst-case fairness guarantees.
         */
        if (backshifted && bfq_gt(st->vtime, entity->finish)) {
                unsigned long delta = st->vtime - entity->finish;

                entity->start += delta;
                entity->finish += delta;
        }

        bfq_active_insert(st, entity);
}

/**
 * __bfq_activate_entity - handle activation of entity.
 * @entity: the entity being activated.
 * @non_blocking_wait_rq: true if entity was waiting for a request
 *
 * Called for a 'true' activation, i.e., if entity is not active and
 * one of its children receives a new request.
 *
 * Basically, this function updates the timestamps of entity and
 * inserts entity into its active tree, ater possible extracting it
 * from its idle tree.
 */
static void __bfq_activate_entity(struct bfq_entity *entity,
                                  bool non_blocking_wait_rq)
{
        struct bfq_service_tree *st = bfq_entity_service_tree(entity);
        bool backshifted = false;
        unsigned long long min_vstart;

        /* See comments on bfq_fqq_update_budg_for_activation */
        if (non_blocking_wait_rq && bfq_gt(st->vtime, entity->finish)) {
                backshifted = true;
                min_vstart = entity->finish;
        } else
                min_vstart = st->vtime;

        if (entity->tree == &st->idle) {
                /*
                 * Must be on the idle tree, bfq_idle_extract() will
                 * check for that.
                 */
                bfq_idle_extract(st, entity);
                entity->start = bfq_gt(min_vstart, entity->finish) ?
                        min_vstart : entity->finish;
        } else {
                /*
                 * The finish time of the entity may be invalid, and
                 * it is in the past for sure, otherwise the queue
                 * would have been on the idle tree.
                 */
                entity->start = min_vstart;
                st->wsum += entity->weight;
                /*
                 * entity is about to be inserted into a service tree,
                 * and then set in service: get a reference to make
                 * sure entity does not disappear until it is no
                 * longer in service or scheduled for service.
                 */
                bfq_get_entity(entity);

                entity->on_st = true;
        }

        bfq_update_fin_time_enqueue(entity, st, backshifted);
}

/**
 * __bfq_requeue_entity - handle requeueing or repositioning of an entity.
 * @entity: the entity being requeued or repositioned.
 *
 * Requeueing is needed if this entity stops being served, which
 * happens if a leaf descendant entity has expired. On the other hand,
 * repositioning is needed if the next_inservice_entity for the child
 * entity has changed. See the comments inside the function for
 * details.
 *
 * Basically, this function: 1) removes entity from its active tree if
 * present there, 2) updates the timestamps of entity and 3) inserts
 * entity back into its active tree (in the new, right position for
 * the new values of the timestamps).
 */
static void __bfq_requeue_entity(struct bfq_entity *entity)
{
        struct bfq_sched_data *sd = entity->sched_data;
        struct bfq_service_tree *st = bfq_entity_service_tree(entity);

        if (entity == sd->in_service_entity) {
                /*
                 * We are requeueing the current in-service entity,
                 * which may have to be done for one of the following
                 * reasons:
                 * - entity represents the in-service queue, and the
                 *   in-service queue is being requeued after an
                 *   expiration;
                 * - entity represents a group, and its budget has
                 *   changed because one of its child entities has
                 *   just been either activated or requeued for some
                 *   reason; the timestamps of the entity need then to
                 *   be updated, and the entity needs to be enqueued
                 *   or repositioned accordingly.
                 *
                 * In particular, before requeueing, the start time of
                 * the entity must be moved forward to account for the
                 * service that the entity has received while in
                 * service. This is done by the next instructions. The
                 * finish time will then be updated according to this
                 * new value of the start time, and to the budget of
                 * the entity.
                 */
                bfq_calc_finish(entity, entity->service);
                entity->start = entity->finish;
                /*
                 * In addition, if the entity had more than one child
                 * when set in service, then was not extracted from
                 * the active tree. This implies that the position of
                 * the entity in the active tree may need to be
                 * changed now, because we have just updated the start
                 * time of the entity, and we will update its finish
                 * time in a moment (the requeueing is then, more
                 * precisely, a repositioning in this case). To
                 * implement this repositioning, we: 1) dequeue the
                 * entity here, 2) update the finish time and
                 * requeue the entity according to the new
                 * timestamps below.
                 */
                if (entity->tree)
                        bfq_active_extract(st, entity);
        } else { /* The entity is already active, and not in service */
                /*
                 * In this case, this function gets called only if the
                 * next_in_service entity below this entity has
                 * changed, and this change has caused the budget of
                 * this entity to change, which, finally implies that
                 * the finish time of this entity must be
                 * updated. Such an update may cause the scheduling,
                 * i.e., the position in the active tree, of this
                 * entity to change. We handle this change by: 1)
                 * dequeueing the entity here, 2) updating the finish
                 * time and requeueing the entity according to the new
                 * timestamps below. This is the same approach as the
                 * non-extracted-entity sub-case above.
                 */
                bfq_active_extract(st, entity);
        }

        bfq_update_fin_time_enqueue(entity, st, false);
}

static void __bfq_activate_requeue_entity(struct bfq_entity *entity,
                                          struct bfq_sched_data *sd,
                                          bool non_blocking_wait_rq)
{
        struct bfq_service_tree *st = bfq_entity_service_tree(entity);

        if (sd->in_service_entity == entity || entity->tree == &st->active)
                 /*
                  * in service or already queued on the active tree,
                  * requeue or reposition
                  */
                __bfq_requeue_entity(entity);
        else
                /*
                 * Not in service and not queued on its active tree:
                 * the activity is idle and this is a true activation.
                 */
                __bfq_activate_entity(entity, non_blocking_wait_rq);
}


/**
 * bfq_activate_entity - activate or requeue an entity representing a bfq_queue,
 *                       and activate, requeue or reposition all ancestors
 *                       for which such an update becomes necessary.
 * @entity: the entity to activate.
 * @non_blocking_wait_rq: true if this entity was waiting for a request
 * @requeue: true if this is a requeue, which implies that bfqq is
 *           being expired; thus ALL its ancestors stop being served and must
 *           therefore be requeued
 */
static void bfq_activate_requeue_entity(struct bfq_entity *entity,
                                        bool non_blocking_wait_rq,
                                        bool requeue)
{
        struct bfq_sched_data *sd;

        for_each_entity(entity) {
                sd = entity->sched_data;
                __bfq_activate_requeue_entity(entity, sd, non_blocking_wait_rq);

                if (!bfq_update_next_in_service(sd, entity) && !requeue)
                        break;
        }
}

/**
 * __bfq_deactivate_entity - deactivate an entity from its service tree.
 * @entity: the entity to deactivate.
 * @ins_into_idle_tree: if false, the entity will not be put into the
 *                      idle tree.
 *
 * Deactivates an entity, independently from its previous state.  Must
 * be invoked only if entity is on a service tree. Extracts the entity
 * from that tree, and if necessary and allowed, puts it on the idle
 * tree.
 */
static bool __bfq_deactivate_entity(struct bfq_entity *entity,
                                    bool ins_into_idle_tree)
{
        struct bfq_sched_data *sd = entity->sched_data;
        struct bfq_service_tree *st = bfq_entity_service_tree(entity);
        int is_in_service = entity == sd->in_service_entity;

        if (!entity->on_st) /* entity never activated, or already inactive */
                return false;

        if (is_in_service)
                bfq_calc_finish(entity, entity->service);

        if (entity->tree == &st->active)
                bfq_active_extract(st, entity);
        else if (!is_in_service && entity->tree == &st->idle)
                bfq_idle_extract(st, entity);

        if (!ins_into_idle_tree || !bfq_gt(entity->finish, st->vtime))
                bfq_forget_entity(st, entity, is_in_service);
        else
                bfq_idle_insert(st, entity);

        return true;
}

/**
 * bfq_deactivate_entity - deactivate an entity representing a bfq_queue.
 * @entity: the entity to deactivate.
 * @ins_into_idle_tree: true if the entity can be put on the idle tree
 */
static void bfq_deactivate_entity(struct bfq_entity *entity,
                                  bool ins_into_idle_tree,
                                  bool expiration)
{
        struct bfq_sched_data *sd;
        struct bfq_entity *parent = NULL;

        for_each_entity_safe(entity, parent) {
                sd = entity->sched_data;

                if (!__bfq_deactivate_entity(entity, ins_into_idle_tree)) {
                        /*
                         * entity is not in any tree any more, so
                         * this deactivation is a no-op, and there is
                         * nothing to change for upper-level entities
                         * (in case of expiration, this can never
                         * happen).
                         */
                        return;
                }

                if (sd->next_in_service == entity)
                        /*
                         * entity was the next_in_service entity,
                         * then, since entity has just been
                         * deactivated, a new one must be found.
                         */
                        bfq_update_next_in_service(sd, NULL);

                if (sd->next_in_service)
                        /*
                         * The parent entity is still backlogged,
                         * because next_in_service is not NULL. So, no
                         * further upwards deactivation must be
                         * performed.  Yet, next_in_service has
                         * changed.  Then the schedule does need to be
                         * updated upwards.
                         */
                        break;

                /*
                 * If we get here, then the parent is no more
                 * backlogged and we need to propagate the
                 * deactivation upwards. Thus let the loop go on.
                 */

                /*
                 * Also let parent be queued into the idle tree on
                 * deactivation, to preserve service guarantees, and
                 * assuming that who invoked this function does not
                 * need parent entities too to be removed completely.
                 */
                ins_into_idle_tree = true;
        }

        /*
         * If the deactivation loop is fully executed, then there are
         * no more entities to touch and next loop is not executed at
         * all. Otherwise, requeue remaining entities if they are
         * about to stop receiving service, or reposition them if this
         * is not the case.
         */
        entity = parent;
        for_each_entity(entity) {
                /*
                 * Invoke __bfq_requeue_entity on entity, even if
                 * already active, to requeue/reposition it in the
                 * active tree (because sd->next_in_service has
                 * changed)
                 */
                __bfq_requeue_entity(entity);

                sd = entity->sched_data;
                if (!bfq_update_next_in_service(sd, entity) &&
                    !expiration)
                        /*
                         * next_in_service unchanged or not causing
                         * any change in entity->parent->sd, and no
                         * requeueing needed for expiration: stop
                         * here.
                         */
                        break;
        }
}

/**
 * bfq_calc_vtime_jump - compute the value to which the vtime should jump,
 *                       if needed, to have at least one entity eligible.
 * @st: the service tree to act upon.
 *
 * Assumes that st is not empty.
 */
static u64 bfq_calc_vtime_jump(struct bfq_service_tree *st)
{
        struct bfq_entity *root_entity = bfq_root_active_entity(&st->active);

        if (bfq_gt(root_entity->min_start, st->vtime))
                return root_entity->min_start;

        return st->vtime;
}

static void bfq_update_vtime(struct bfq_service_tree *st, u64 new_value)
{
        if (new_value > st->vtime) {
                st->vtime = new_value;
                bfq_forget_idle(st);
        }
}

/**
 * bfq_first_active_entity - find the eligible entity with
 *                           the smallest finish time
 * @st: the service tree to select from.
 * @vtime: the system virtual to use as a reference for eligibility
 *
 * This function searches the first schedulable entity, starting from the
 * root of the tree and going on the left every time on this side there is
 * a subtree with at least one eligible (start >= vtime) entity. The path on
 * the right is followed only if a) the left subtree contains no eligible
 * entities and b) no eligible entity has been found yet.
 */
static struct bfq_entity *bfq_first_active_entity(struct bfq_service_tree *st,
                                                  u64 vtime)
{
        struct bfq_entity *entry, *first = NULL;
        struct rb_node *node = st->active.rb_node;

        while (node) {
                entry = rb_entry(node, struct bfq_entity, rb_node);
left:
                if (!bfq_gt(entry->start, vtime))
                        first = entry;

                if (node->rb_left) {
                        entry = rb_entry(node->rb_left,
                                         struct bfq_entity, rb_node);
                        if (!bfq_gt(entry->min_start, vtime)) {
                                node = node->rb_left;
                                goto left;
                        }
                }
                if (first)
                        break;
                node = node->rb_right;
        }

        return first;
}

/**
 * __bfq_lookup_next_entity - return the first eligible entity in @st.
 * @st: the service tree.
 *
 * If there is no in-service entity for the sched_data st belongs to,
 * then return the entity that will be set in service if:
 * 1) the parent entity this st belongs to is set in service;
 * 2) no entity belonging to such parent entity undergoes a state change
 * that would influence the timestamps of the entity (e.g., becomes idle,
 * becomes backlogged, changes its budget, ...).
 *
 * In this first case, update the virtual time in @st too (see the
 * comments on this update inside the function).
 *
 * In constrast, if there is an in-service entity, then return the
 * entity that would be set in service if not only the above
 * conditions, but also the next one held true: the currently
 * in-service entity, on expiration,
 * 1) gets a finish time equal to the current one, or
 * 2) is not eligible any more, or
 * 3) is idle.
 */
static struct bfq_entity *
__bfq_lookup_next_entity(struct bfq_service_tree *st, bool in_service)
{
        struct bfq_entity *entity;
        u64 new_vtime;

        if (RB_EMPTY_ROOT(&st->active))
                return NULL;

        /*
         * Get the value of the system virtual time for which at
         * least one entity is eligible.
         */
        new_vtime = bfq_calc_vtime_jump(st);

        /*
         * If there is no in-service entity for the sched_data this
         * active tree belongs to, then push the system virtual time
         * up to the value that guarantees that at least one entity is
         * eligible. If, instead, there is an in-service entity, then
         * do not make any such update, because there is already an
         * eligible entity, namely the in-service one (even if the
         * entity is not on st, because it was extracted when set in
         * service).
         */
        if (!in_service)
                bfq_update_vtime(st, new_vtime);

        entity = bfq_first_active_entity(st, new_vtime);

        return entity;
}

/**
 * bfq_lookup_next_entity - return the first eligible entity in @sd.
 * @sd: the sched_data.
 *
 * This function is invoked when there has been a change in the trees
 * for sd, and we need know what is the new next entity after this
 * change.
 */
static struct bfq_entity *bfq_lookup_next_entity(struct bfq_sched_data *sd)
{
        struct bfq_service_tree *st = sd->service_tree;
        struct bfq_service_tree *idle_class_st = st + (BFQ_IOPRIO_CLASSES - 1);
        struct bfq_entity *entity = NULL;
        int class_idx = 0;

        /*
         * Choose from idle class, if needed to guarantee a minimum
         * bandwidth to this class (and if there is some active entity
         * in idle class). This should also mitigate
         * priority-inversion problems in case a low priority task is
         * holding file system resources.
         */
        if (time_is_before_jiffies(sd->bfq_class_idle_last_service +
                                   BFQ_CL_IDLE_TIMEOUT)) {
                if (!RB_EMPTY_ROOT(&idle_class_st->active))
                        class_idx = BFQ_IOPRIO_CLASSES - 1;
                /* About to be served if backlogged, or not yet backlogged */
                sd->bfq_class_idle_last_service = jiffies;
        }

        /*
         * Find the next entity to serve for the highest-priority
         * class, unless the idle class needs to be served.
         */
        for (; class_idx < BFQ_IOPRIO_CLASSES; class_idx++) {
                entity = __bfq_lookup_next_entity(st + class_idx,
                                                  sd->in_service_entity);

                if (entity)
                        break;
        }

        if (!entity)
                return NULL;

        return entity;
}

static bool next_queue_may_preempt(struct bfq_data *bfqd)
{
        struct bfq_sched_data *sd = &bfqd->root_group->sched_data;

        return sd->next_in_service != sd->in_service_entity;
}

/*
 * Get next queue for service.
 */
static struct bfq_queue *bfq_get_next_queue(struct bfq_data *bfqd)
{
        struct bfq_entity *entity = NULL;
        struct bfq_sched_data *sd;
        struct bfq_queue *bfqq;

        if (bfqd->busy_queues == 0)
                return NULL;

        /*
         * Traverse the path from the root to the leaf entity to
         * serve. Set in service all the entities visited along the
         * way.
         */
        sd = &bfqd->root_group->sched_data;
        for (; sd ; sd = entity->my_sched_data) {
                /*
                 * WARNING. We are about to set the in-service entity
                 * to sd->next_in_service, i.e., to the (cached) value
                 * returned by bfq_lookup_next_entity(sd) the last
                 * time it was invoked, i.e., the last time when the
                 * service order in sd changed as a consequence of the
                 * activation or deactivation of an entity. In this
                 * respect, if we execute bfq_lookup_next_entity(sd)
                 * in this very moment, it may, although with low
                 * probability, yield a different entity than that
                 * pointed to by sd->next_in_service. This rare event
                 * happens in case there was no CLASS_IDLE entity to
                 * serve for sd when bfq_lookup_next_entity(sd) was
                 * invoked for the last time, while there is now one
                 * such entity.
                 *
                 * If the above event happens, then the scheduling of
                 * such entity in CLASS_IDLE is postponed until the
                 * service of the sd->next_in_service entity
                 * finishes. In fact, when the latter is expired,
                 * bfq_lookup_next_entity(sd) gets called again,
                 * exactly to update sd->next_in_service.
                 */

                /* Make next_in_service entity become in_service_entity */
                entity = sd->next_in_service;
                sd->in_service_entity = entity;

                /*
                 * Reset the accumulator of the amount of service that
                 * the entity is about to receive.
                 */
                entity->service = 0;

                /*
                 * If entity is no longer a candidate for next
                 * service, then we extract it from its active tree,
                 * for the following reason. To further boost the
                 * throughput in some special case, BFQ needs to know
                 * which is the next candidate entity to serve, while
                 * there is already an entity in service. In this
                 * respect, to make it easy to compute/update the next
                 * candidate entity to serve after the current
                 * candidate has been set in service, there is a case
                 * where it is necessary to extract the current
                 * candidate from its service tree. Such a case is
                 * when the entity just set in service cannot be also
                 * a candidate for next service. Details about when
                 * this conditions holds are reported in the comments
                 * on the function bfq_no_longer_next_in_service()
                 * invoked below.
                 */
                if (bfq_no_longer_next_in_service(entity))
                        bfq_active_extract(bfq_entity_service_tree(entity),
                                           entity);

                /*
                 * For the same reason why we may have just extracted
                 * entity from its active tree, we may need to update
                 * next_in_service for the sched_data of entity too,
                 * regardless of whether entity has been extracted.
                 * In fact, even if entity has not been extracted, a
                 * descendant entity may get extracted. Such an event
                 * would cause a change in next_in_service for the
                 * level of the descendant entity, and thus possibly
                 * back to upper levels.
                 *
                 * We cannot perform the resulting needed update
                 * before the end of this loop, because, to know which
                 * is the correct next-to-serve candidate entity for
                 * each level, we need first to find the leaf entity
                 * to set in service. In fact, only after we know
                 * which is the next-to-serve leaf entity, we can
                 * discover whether the parent entity of the leaf
                 * entity becomes the next-to-serve, and so on.
                 */

        }

        bfqq = bfq_entity_to_bfqq(entity);

        /*
         * We can finally update all next-to-serve entities along the
         * path from the leaf entity just set in service to the root.
         */
        for_each_entity(entity) {
                struct bfq_sched_data *sd = entity->sched_data;

                if (!bfq_update_next_in_service(sd, NULL))
                        break;
        }

        return bfqq;
}

static void __bfq_bfqd_reset_in_service(struct bfq_data *bfqd)
{
        struct bfq_queue *in_serv_bfqq = bfqd->in_service_queue;
        struct bfq_entity *in_serv_entity = &in_serv_bfqq->entity;
        struct bfq_entity *entity = in_serv_entity;

        if (bfqd->in_service_bic) {
                put_io_context(bfqd->in_service_bic->icq.ioc);
                bfqd->in_service_bic = NULL;
        }

        bfq_clear_bfqq_wait_request(in_serv_bfqq);
        hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
        bfqd->in_service_queue = NULL;

        /*
         * When this function is called, all in-service entities have
         * been properly deactivated or requeued, so we can safely
         * execute the final step: reset in_service_entity along the
         * path from entity to the root.
         */
        for_each_entity(entity)
                entity->sched_data->in_service_entity = NULL;

        /*
         * in_serv_entity is no longer in service, so, if it is in no
         * service tree either, then release the service reference to
         * the queue it represents (taken with bfq_get_entity).
         */
        if (!in_serv_entity->on_st)
                bfq_put_queue(in_serv_bfqq);
}

static void bfq_deactivate_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
                                bool ins_into_idle_tree, bool expiration)
{
        struct bfq_entity *entity = &bfqq->entity;

        bfq_deactivate_entity(entity, ins_into_idle_tree, expiration);
}

static void bfq_activate_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
{
        struct bfq_entity *entity = &bfqq->entity;

        bfq_activate_requeue_entity(entity, bfq_bfqq_non_blocking_wait_rq(bfqq),
                                    false);
        bfq_clear_bfqq_non_blocking_wait_rq(bfqq);
}

static void bfq_requeue_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
{
        struct bfq_entity *entity = &bfqq->entity;

        bfq_activate_requeue_entity(entity, false,
                                    bfqq == bfqd->in_service_queue);
}

static void bfqg_stats_update_dequeue(struct bfq_group *bfqg);

/*
 * Called when the bfqq no longer has requests pending, remove it from
 * the service tree. As a special case, it can be invoked during an
 * expiration.
 */
static void bfq_del_bfqq_busy(struct bfq_data *bfqd, struct bfq_queue *bfqq,
                              bool expiration)
{
        bfq_log_bfqq(bfqd, bfqq, "del from busy");

        bfq_clear_bfqq_busy(bfqq);

        bfqd->busy_queues--;

        bfqg_stats_update_dequeue(bfqq_group(bfqq));

        bfq_deactivate_bfqq(bfqd, bfqq, true, expiration);
}

/*
 * Called when an inactive queue receives a new request.
 */
static void bfq_add_bfqq_busy(struct bfq_data *bfqd, struct bfq_queue *bfqq)
{
        bfq_log_bfqq(bfqd, bfqq, "add to busy");

        bfq_activate_bfqq(bfqd, bfqq);

        bfq_mark_bfqq_busy(bfqq);
        bfqd->busy_queues++;
}

#ifdef CONFIG_BFQ_GROUP_IOSCHED

/* bfqg stats flags */
enum bfqg_stats_flags {
        BFQG_stats_waiting = 0,
        BFQG_stats_idling,
        BFQG_stats_empty,
};

#define BFQG_FLAG_FNS(name)                                             \
static void bfqg_stats_mark_##name(struct bfqg_stats *stats)    \
{                                                                       \
        stats->flags |= (1 << BFQG_stats_##name);                       \
}                                                                       \
static void bfqg_stats_clear_##name(struct bfqg_stats *stats)   \
{                                                                       \
        stats->flags &= ~(1 << BFQG_stats_##name);                      \
}                                                                       \
static int bfqg_stats_##name(struct bfqg_stats *stats)          \
{                                                                       \
        return (stats->flags & (1 << BFQG_stats_##name)) != 0;          \
}                                                                       \

BFQG_FLAG_FNS(waiting)
BFQG_FLAG_FNS(idling)
BFQG_FLAG_FNS(empty)
#undef BFQG_FLAG_FNS

/* This should be called with the queue_lock held. */
static void bfqg_stats_update_group_wait_time(struct bfqg_stats *stats)
{
        unsigned long long now;

        if (!bfqg_stats_waiting(stats))
                return;

        now = sched_clock();
        if (time_after64(now, stats->start_group_wait_time))
                blkg_stat_add(&stats->group_wait_time,
                              now - stats->start_group_wait_time);
        bfqg_stats_clear_waiting(stats);
}

/* This should be called with the queue_lock held. */
static void bfqg_stats_set_start_group_wait_time(struct bfq_group *bfqg,
                                                 struct bfq_group *curr_bfqg)
{
        struct bfqg_stats *stats = &bfqg->stats;

        if (bfqg_stats_waiting(stats))
                return;
        if (bfqg == curr_bfqg)
                return;
        stats->start_group_wait_time = sched_clock();
        bfqg_stats_mark_waiting(stats);
}

/* This should be called with the queue_lock held. */
static void bfqg_stats_end_empty_time(struct bfqg_stats *stats)
{
        unsigned long long now;

        if (!bfqg_stats_empty(stats))
                return;

        now = sched_clock();
        if (time_after64(now, stats->start_empty_time))
                blkg_stat_add(&stats->empty_time,
                              now - stats->start_empty_time);
        bfqg_stats_clear_empty(stats);
}

static void bfqg_stats_update_dequeue(struct bfq_group *bfqg)
{
        blkg_stat_add(&bfqg->stats.dequeue, 1);
}

static void bfqg_stats_set_start_empty_time(struct bfq_group *bfqg)
{
        struct bfqg_stats *stats = &bfqg->stats;

        if (blkg_rwstat_total(&stats->queued))
                return;

        /*
         * group is already marked empty. This can happen if bfqq got new
         * request in parent group and moved to this group while being added
         * to service tree. Just ignore the event and move on.
         */
        if (bfqg_stats_empty(stats))
                return;

        stats->start_empty_time = sched_clock();
        bfqg_stats_mark_empty(stats);
}

static void bfqg_stats_update_idle_time(struct bfq_group *bfqg)
{
        struct bfqg_stats *stats = &bfqg->stats;

        if (bfqg_stats_idling(stats)) {
                unsigned long long now = sched_clock();

                if (time_after64(now, stats->start_idle_time))
                        blkg_stat_add(&stats->idle_time,
                                      now - stats->start_idle_time);
                bfqg_stats_clear_idling(stats);
        }
}

static void bfqg_stats_set_start_idle_time(struct bfq_group *bfqg)
{
        struct bfqg_stats *stats = &bfqg->stats;

        stats->start_idle_time = sched_clock();
        bfqg_stats_mark_idling(stats);
}

static void bfqg_stats_update_avg_queue_size(struct bfq_group *bfqg)
{
        struct bfqg_stats *stats = &bfqg->stats;

        blkg_stat_add(&stats->avg_queue_size_sum,
                      blkg_rwstat_total(&stats->queued));
        blkg_stat_add(&stats->avg_queue_size_samples, 1);
        bfqg_stats_update_group_wait_time(stats);
}

/*
 * blk-cgroup policy-related handlers
 * The following functions help in converting between blk-cgroup
 * internal structures and BFQ-specific structures.
 */

static struct bfq_group *pd_to_bfqg(struct blkg_policy_data *pd)
{
        return pd ? container_of(pd, struct bfq_group, pd) : NULL;
}

static struct blkcg_gq *bfqg_to_blkg(struct bfq_group *bfqg)
{
        return pd_to_blkg(&bfqg->pd);
}

static struct blkcg_policy blkcg_policy_bfq;

static struct bfq_group *blkg_to_bfqg(struct blkcg_gq *blkg)
{
        return pd_to_bfqg(blkg_to_pd(blkg, &blkcg_policy_bfq));
}

/*
 * bfq_group handlers
 * The following functions help in navigating the bfq_group hierarchy
 * by allowing to find the parent of a bfq_group or the bfq_group
 * associated to a bfq_queue.
 */

static struct bfq_group *bfqg_parent(struct bfq_group *bfqg)
{
        struct blkcg_gq *pblkg = bfqg_to_blkg(bfqg)->parent;

        return pblkg ? blkg_to_bfqg(pblkg) : NULL;
}

static struct bfq_group *bfqq_group(struct bfq_queue *bfqq)
{
        struct bfq_entity *group_entity = bfqq->entity.parent;

        return group_entity ? container_of(group_entity, struct bfq_group,
                                           entity) :
                              bfqq->bfqd->root_group;
}

/*
 * The following two functions handle get and put of a bfq_group by
 * wrapping the related blk-cgroup hooks.
 */

static void bfqg_get(struct bfq_group *bfqg)
{
        return blkg_get(bfqg_to_blkg(bfqg));
}

static void bfqg_put(struct bfq_group *bfqg)
{
        return blkg_put(bfqg_to_blkg(bfqg));
}

static void bfqg_stats_update_io_add(struct bfq_group *bfqg,
                                     struct bfq_queue *bfqq,
                                     unsigned int op)
{
        blkg_rwstat_add(&bfqg->stats.queued, op, 1);
        bfqg_stats_end_empty_time(&bfqg->stats);
        if (!(bfqq == ((struct bfq_data *)bfqg->bfqd)->in_service_queue))
                bfqg_stats_set_start_group_wait_time(bfqg, bfqq_group(bfqq));
}

static void bfqg_stats_update_io_remove(struct bfq_group *bfqg, unsigned int op)
{
        blkg_rwstat_add(&bfqg->stats.queued, op, -1);
}

static void bfqg_stats_update_io_merged(struct bfq_group *bfqg, unsigned int op)
{
        blkg_rwstat_add(&bfqg->stats.merged, op, 1);
}

static void bfqg_stats_update_completion(struct bfq_group *bfqg,
                        uint64_t start_time, uint64_t io_start_time,
                        unsigned int op)
{
        struct bfqg_stats *stats = &bfqg->stats;
        unsigned long long now = sched_clock();

        if (time_after64(now, io_start_time))
                blkg_rwstat_add(&stats->service_time, op,
                                now - io_start_time);
        if (time_after64(io_start_time, start_time))
                blkg_rwstat_add(&stats->wait_time, op,
                                io_start_time - start_time);
}

/* @stats = 0 */
static void bfqg_stats_reset(struct bfqg_stats *stats)
{
        /* queued stats shouldn't be cleared */
        blkg_rwstat_reset(&stats->merged);
        blkg_rwstat_reset(&stats->service_time);
        blkg_rwstat_reset(&stats->wait_time);
        blkg_stat_reset(&stats->time);
        blkg_stat_reset(&stats->avg_queue_size_sum);
        blkg_stat_reset(&stats->avg_queue_size_samples);
        blkg_stat_reset(&stats->dequeue);
        blkg_stat_reset(&stats->group_wait_time);
        blkg_stat_reset(&stats->idle_time);
        blkg_stat_reset(&stats->empty_time);
}

/* @to += @from */
static void bfqg_stats_add_aux(struct bfqg_stats *to, struct bfqg_stats *from)
{
        if (!to || !from)
                return;

        /* queued stats shouldn't be cleared */
        blkg_rwstat_add_aux(&to->merged, &from->merged);
        blkg_rwstat_add_aux(&to->service_time, &from->service_time);
        blkg_rwstat_add_aux(&to->wait_time, &from->wait_time);
        blkg_stat_add_aux(&from->time, &from->time);
        blkg_stat_add_aux(&to->avg_queue_size_sum, &from->avg_queue_size_sum);
        blkg_stat_add_aux(&to->avg_queue_size_samples,
                          &from->avg_queue_size_samples);
        blkg_stat_add_aux(&to->dequeue, &from->dequeue);
        blkg_stat_add_aux(&to->group_wait_time, &from->group_wait_time);
        blkg_stat_add_aux(&to->idle_time, &from->idle_time);
        blkg_stat_add_aux(&to->empty_time, &from->empty_time);
}

/*
 * Transfer @bfqg's stats to its parent's aux counts so that the ancestors'
 * recursive stats can still account for the amount used by this bfqg after
 * it's gone.
 */
static void bfqg_stats_xfer_dead(struct bfq_group *bfqg)
{
        struct bfq_group *parent;

        if (!bfqg) /* root_group */
                return;

        parent = bfqg_parent(bfqg);

        lockdep_assert_held(bfqg_to_blkg(bfqg)->q->queue_lock);

        if (unlikely(!parent))
                return;

        bfqg_stats_add_aux(&parent->stats, &bfqg->stats);
        bfqg_stats_reset(&bfqg->stats);
}

static void bfq_init_entity(struct bfq_entity *entity,
                            struct bfq_group *bfqg)
{
        struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);

        entity->weight = entity->new_weight;
        entity->orig_weight = entity->new_weight;
        if (bfqq) {
                bfqq->ioprio = bfqq->new_ioprio;
                bfqq->ioprio_class = bfqq->new_ioprio_class;
                bfqg_get(bfqg);
        }
        entity->parent = bfqg->my_entity; /* NULL for root group */
        entity->sched_data = &bfqg->sched_data;
}

static void bfqg_stats_exit(struct bfqg_stats *stats)
{
        blkg_rwstat_exit(&stats->merged);
        blkg_rwstat_exit(&stats->service_time);
        blkg_rwstat_exit(&stats->wait_time);
        blkg_rwstat_exit(&stats->queued);
        blkg_stat_exit(&stats->time);
        blkg_stat_exit(&stats->avg_queue_size_sum);
        blkg_stat_exit(&stats->avg_queue_size_samples);
        blkg_stat_exit(&stats->dequeue);
        blkg_stat_exit(&stats->group_wait_time);
        blkg_stat_exit(&stats->idle_time);
        blkg_stat_exit(&stats->empty_time);
}

static int bfqg_stats_init(struct bfqg_stats *stats, gfp_t gfp)
{
        if (blkg_rwstat_init(&stats->merged, gfp) ||
            blkg_rwstat_init(&stats->service_time, gfp) ||
            blkg_rwstat_init(&stats->wait_time, gfp) ||
            blkg_rwstat_init(&stats->queued, gfp) ||
            blkg_stat_init(&stats->time, gfp) ||
            blkg_stat_init(&stats->avg_queue_size_sum, gfp) ||
            blkg_stat_init(&stats->avg_queue_size_samples, gfp) ||
            blkg_stat_init(&stats->dequeue, gfp) ||
            blkg_stat_init(&stats->group_wait_time, gfp) ||
            blkg_stat_init(&stats->idle_time, gfp) ||
            blkg_stat_init(&stats->empty_time, gfp)) {
                bfqg_stats_exit(stats);
                return -ENOMEM;
        }

        return 0;
}

static struct bfq_group_data *cpd_to_bfqgd(struct blkcg_policy_data *cpd)
{
        return cpd ? container_of(cpd, struct bfq_group_data, pd) : NULL;
}

static struct bfq_group_data *blkcg_to_bfqgd(struct blkcg *blkcg)
{
        return cpd_to_bfqgd(blkcg_to_cpd(blkcg, &blkcg_policy_bfq));
}

static struct blkcg_policy_data *bfq_cpd_alloc(gfp_t gfp)
{
        struct bfq_group_data *bgd;

        bgd = kzalloc(sizeof(*bgd), gfp);
        if (!bgd)
                return NULL;
        return &bgd->pd;
}

static void bfq_cpd_init(struct blkcg_policy_data *cpd)
{
        struct bfq_group_data *d = cpd_to_bfqgd(cpd);

        d->weight = cgroup_subsys_on_dfl(io_cgrp_subsys) ?
                CGROUP_WEIGHT_DFL : BFQ_WEIGHT_LEGACY_DFL;
}

static void bfq_cpd_free(struct blkcg_policy_data *cpd)
{
        kfree(cpd_to_bfqgd(cpd));
}

static struct blkg_policy_data *bfq_pd_alloc(gfp_t gfp, int node)
{
        struct bfq_group *bfqg;

        bfqg = kzalloc_node(sizeof(*bfqg), gfp, node);
        if (!bfqg)
                return NULL;

        if (bfqg_stats_init(&bfqg->stats, gfp)) {
                kfree(bfqg);
                return NULL;
        }

        return &bfqg->pd;
}

static void bfq_pd_init(struct blkg_policy_data *pd)
{
        struct blkcg_gq *blkg = pd_to_blkg(pd);
        struct bfq_group *bfqg = blkg_to_bfqg(blkg);
        struct bfq_data *bfqd = blkg->q->elevator->elevator_data;
        struct bfq_entity *entity = &bfqg->entity;
        struct bfq_group_data *d = blkcg_to_bfqgd(blkg->blkcg);

        entity->orig_weight = entity->weight = entity->new_weight = d->weight;
        entity->my_sched_data = &bfqg->sched_data;
        bfqg->my_entity = entity; /*
                                   * the root_group's will be set to NULL
                                   * in bfq_init_queue()
                                   */
        bfqg->bfqd = bfqd;
}

static void bfq_pd_free(struct blkg_policy_data *pd)
{
        struct bfq_group *bfqg = pd_to_bfqg(pd);

        bfqg_stats_exit(&bfqg->stats);
        return kfree(bfqg);
}

static void bfq_pd_reset_stats(struct blkg_policy_data *pd)
{
        struct bfq_group *bfqg = pd_to_bfqg(pd);

        bfqg_stats_reset(&bfqg->stats);
}

static void bfq_group_set_parent(struct bfq_group *bfqg,
                                        struct bfq_group *parent)
{
        struct bfq_entity *entity;

        entity = &bfqg->entity;
        entity->parent = parent->my_entity;
        entity->sched_data = &parent->sched_data;
}

static struct bfq_group *bfq_lookup_bfqg(struct bfq_data *bfqd,
                                         struct blkcg *blkcg)
{
        struct blkcg_gq *blkg;

        blkg = blkg_lookup(blkcg, bfqd->queue);
        if (likely(blkg))
                return blkg_to_bfqg(blkg);
        return NULL;
}

static struct bfq_group *bfq_find_set_group(struct bfq_data *bfqd,
                                            struct blkcg *blkcg)
{
        struct bfq_group *bfqg, *parent;
        struct bfq_entity *entity;

        bfqg = bfq_lookup_bfqg(bfqd, blkcg);

        if (unlikely(!bfqg))
                return NULL;

        /*
         * Update chain of bfq_groups as we might be handling a leaf group
         * which, along with some of its relatives, has not been hooked yet
         * to the private hierarchy of BFQ.
         */
        entity = &bfqg->entity;
        for_each_entity(entity) {
                bfqg = container_of(entity, struct bfq_group, entity);
                if (bfqg != bfqd->root_group) {
                        parent = bfqg_parent(bfqg);
                        if (!parent)
                                parent = bfqd->root_group;
                        bfq_group_set_parent(bfqg, parent);
                }
        }

        return bfqg;
}

static void bfq_bfqq_expire(struct bfq_data *bfqd,
                            struct bfq_queue *bfqq,
                            bool compensate,
                            enum bfqq_expiration reason);

/**
 * bfq_bfqq_move - migrate @bfqq to @bfqg.
 * @bfqd: queue descriptor.
 * @bfqq: the queue to move.
 * @bfqg: the group to move to.
 *
 * Move @bfqq to @bfqg, deactivating it from its old group and reactivating
 * it on the new one.  Avoid putting the entity on the old group idle tree.
 *
 * Must be called under the queue lock; the cgroup owning @bfqg must
 * not disappear (by now this just means that we are called under
 * rcu_read_lock()).
 */
static void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq,
                          struct bfq_group *bfqg)
{
        struct bfq_entity *entity = &bfqq->entity;

        /* If bfqq is empty, then bfq_bfqq_expire also invokes
         * bfq_del_bfqq_busy, thereby removing bfqq and its entity
         * from data structures related to current group. Otherwise we
         * need to remove bfqq explicitly with bfq_deactivate_bfqq, as
         * we do below.
         */
        if (bfqq == bfqd->in_service_queue)
                bfq_bfqq_expire(bfqd, bfqd->in_service_queue,
                                false, BFQQE_PREEMPTED);

        if (bfq_bfqq_busy(bfqq))
                bfq_deactivate_bfqq(bfqd, bfqq, false, false);
        else if (entity->on_st)
                bfq_put_idle_entity(bfq_entity_service_tree(entity), entity);
        bfqg_put(bfqq_group(bfqq));

        /*
         * Here we use a reference to bfqg.  We don't need a refcounter
         * as the cgroup reference will not be dropped, so that its
         * destroy() callback will not be invoked.
         */
        entity->parent = bfqg->my_entity;
        entity->sched_data = &bfqg->sched_data;
        bfqg_get(bfqg);

        if (bfq_bfqq_busy(bfqq))
                bfq_activate_bfqq(bfqd, bfqq);

        if (!bfqd->in_service_queue && !bfqd->rq_in_driver)
                bfq_schedule_dispatch(bfqd);
}

/**
 * __bfq_bic_change_cgroup - move @bic to @cgroup.
 * @bfqd: the queue descriptor.
 * @bic: the bic to move.
 * @blkcg: the blk-cgroup to move to.
 *
 * Move bic to blkcg, assuming that bfqd->queue is locked; the caller
 * has to make sure that the reference to cgroup is valid across the call.
 *
 * NOTE: an alternative approach might have been to store the current
 * cgroup in bfqq and getting a reference to it, reducing the lookup
 * time here, at the price of slightly more complex code.
 */
static struct bfq_group *__bfq_bic_change_cgroup(struct bfq_data *bfqd,
                                                struct bfq_io_cq *bic,
                                                struct blkcg *blkcg)
{
        struct bfq_queue *async_bfqq = bic_to_bfqq(bic, 0);
        struct bfq_queue *sync_bfqq = bic_to_bfqq(bic, 1);
        struct bfq_group *bfqg;
        struct bfq_entity *entity;

        bfqg = bfq_find_set_group(bfqd, blkcg);

        if (unlikely(!bfqg))
                bfqg = bfqd->root_group;

        if (async_bfqq) {
                entity = &async_bfqq->entity;

                if (entity->sched_data != &bfqg->sched_data) {
                        bic_set_bfqq(bic, NULL, 0);
                        bfq_log_bfqq(bfqd, async_bfqq,
                                     "bic_change_group: %p %d",
                                     async_bfqq,
                                     async_bfqq->ref);
                        bfq_put_queue(async_bfqq);
                }
        }

        if (sync_bfqq) {
                entity = &sync_bfqq->entity;
                if (entity->sched_data != &bfqg->sched_data)
                        bfq_bfqq_move(bfqd, sync_bfqq, bfqg);
        }

        return bfqg;
}

static void bfq_bic_update_cgroup(struct bfq_io_cq *bic, struct bio *bio)
{
        struct bfq_data *bfqd = bic_to_bfqd(bic);
        struct bfq_group *bfqg = NULL;
        uint64_t serial_nr;

        rcu_read_lock();
        serial_nr = bio_blkcg(bio)->css.serial_nr;

        /*
         * Check whether blkcg has changed.  The condition may trigger
         * spuriously on a newly created cic but there's no harm.
         */
        if (unlikely(!bfqd) || likely(bic->blkcg_serial_nr == serial_nr))
                goto out;

        bfqg = __bfq_bic_change_cgroup(bfqd, bic, bio_blkcg(bio));
        bic->blkcg_serial_nr = serial_nr;
out:
        rcu_read_unlock();
}

/**
 * bfq_flush_idle_tree - deactivate any entity on the idle tree of @st.
 * @st: the service tree being flushed.
 */
static void bfq_flush_idle_tree(struct bfq_service_tree *st)
{
        struct bfq_entity *entity = st->first_idle;

        for (; entity ; entity = st->first_idle)
                __bfq_deactivate_entity(entity, false);
}

/**
 * bfq_reparent_leaf_entity - move leaf entity to the root_group.
 * @bfqd: the device data structure with the root group.
 * @entity: the entity to move.
 */
static void bfq_reparent_leaf_entity(struct bfq_data *bfqd,
                                     struct bfq_entity *entity)
{
        struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);

        bfq_bfqq_move(bfqd, bfqq, bfqd->root_group);
}

/**
 * bfq_reparent_active_entities - move to the root group all active
 *                                entities.
 * @bfqd: the device data structure with the root group.
 * @bfqg: the group to move from.
 * @st: the service tree with the entities.
 *
 * Needs queue_lock to be taken and reference to be valid over the call.
 */
static void bfq_reparent_active_entities(struct bfq_data *bfqd,
                                         struct bfq_group *bfqg,
                                         struct bfq_service_tree *st)
{
        struct rb_root *active = &st->active;
        struct bfq_entity *entity = NULL;

        if (!RB_EMPTY_ROOT(&st->active))
                entity = bfq_entity_of(rb_first(active));

        for (; entity ; entity = bfq_entity_of(rb_first(active)))
                bfq_reparent_leaf_entity(bfqd, entity);

        if (bfqg->sched_data.in_service_entity)
                bfq_reparent_leaf_entity(bfqd,
                        bfqg->sched_data.in_service_entity);
}

/**
 * bfq_pd_offline - deactivate the entity associated with @pd,
 *                  and reparent its children entities.
 * @pd: descriptor of the policy going offline.
 *
 * blkio already grabs the queue_lock for us, so no need to use
 * RCU-based magic
 */
static void bfq_pd_offline(struct blkg_policy_data *pd)
{
        struct bfq_service_tree *st;
        struct bfq_group *bfqg = pd_to_bfqg(pd);
        struct bfq_data *bfqd = bfqg->bfqd;
        struct bfq_entity *entity = bfqg->my_entity;
        unsigned long flags;
        int i;

        if (!entity) /* root group */
                return;

        spin_lock_irqsave(&bfqd->lock, flags);
        /*
         * Empty all service_trees belonging to this group before
         * deactivating the group itself.
         */
        for (i = 0; i < BFQ_IOPRIO_CLASSES; i++) {
                st = bfqg->sched_data.service_tree + i;

                /*
                 * The idle tree may still contain bfq_queues belonging
                 * to exited task because they never migrated to a different
                 * cgroup from the one being destroyed now.  No one else
                 * can access them so it's safe to act without any lock.
                 */
                bfq_flush_idle_tree(st);

                /*
                 * It may happen that some queues are still active
                 * (busy) upon group destruction (if the corresponding
                 * processes have been forced to terminate). We move
                 * all the leaf entities corresponding to these queues
                 * to the root_group.
                 * Also, it may happen that the group has an entity
                 * in service, which is disconnected from the active
                 * tree: it must be moved, too.
                 * There is no need to put the sync queues, as the
                 * scheduler has taken no reference.
                 */
                bfq_reparent_active_entities(bfqd, bfqg, st);
        }

        __bfq_deactivate_entity(entity, false);
        bfq_put_async_queues(bfqd, bfqg);

        spin_unlock_irqrestore(&bfqd->lock, flags);
        /*
         * @blkg is going offline and will be ignored by
         * blkg_[rw]stat_recursive_sum().  Transfer stats to the parent so
         * that they don't get lost.  If IOs complete after this point, the
         * stats for them will be lost.  Oh well...
         */
        bfqg_stats_xfer_dead(bfqg);
}

static int bfq_io_show_weight(struct seq_file *sf, void *v)
{
        struct blkcg *blkcg = css_to_blkcg(seq_css(sf));
        struct bfq_group_data *bfqgd = blkcg_to_bfqgd(blkcg);
        unsigned int val = 0;

        if (bfqgd)
                val = bfqgd->weight;

        seq_printf(sf, "%u\n", val);

        return 0;
}

static int bfq_io_set_weight_legacy(struct cgroup_subsys_state *css,
                                    struct cftype *cftype,
                                    u64 val)
{
        struct blkcg *blkcg = css_to_blkcg(css);
        struct bfq_group_data *bfqgd = blkcg_to_bfqgd(blkcg);
        struct blkcg_gq *blkg;
        int ret = -ERANGE;

        if (val < BFQ_MIN_WEIGHT || val > BFQ_MAX_WEIGHT)
                return ret;

        ret = 0;
        spin_lock_irq(&blkcg->lock);
        bfqgd->weight = (unsigned short)val;
        hlist_for_each_entry(blkg, &blkcg->blkg_list, blkcg_node) {
                struct bfq_group *bfqg = blkg_to_bfqg(blkg);

                if (!bfqg)
                        continue;
                /*
                 * Setting the prio_changed flag of the entity
                 * to 1 with new_weight == weight would re-set
                 * the value of the weight to its ioprio mapping.
                 * Set the flag only if necessary.
                 */
                if ((unsigned short)val != bfqg->entity.new_weight) {
                        bfqg->entity.new_weight = (unsigned short)val;
                        /*
                         * Make sure that the above new value has been
                         * stored in bfqg->entity.new_weight before
                         * setting the prio_changed flag. In fact,
                         * this flag may be read asynchronously (in
                         * critical sections protected by a different
                         * lock than that held here), and finding this
                         * flag set may cause the execution of the code
                         * for updating parameters whose value may
                         * depend also on bfqg->entity.new_weight (in
                         * __bfq_entity_update_weight_prio).
                         * This barrier makes sure that the new value
                         * of bfqg->entity.new_weight is correctly
                         * seen in that code.
                         */
                        smp_wmb();
                        bfqg->entity.prio_changed = 1;
                }
        }
        spin_unlock_irq(&blkcg->lock);

        return ret;
}

static ssize_t bfq_io_set_weight(struct kernfs_open_file *of,
                                 char *buf, size_t nbytes,
                                 loff_t off)
{
        u64 weight;
        /* First unsigned long found in the file is used */
        int ret = kstrtoull(strim(buf), 0, &weight);

        if (ret)
                return ret;

        return bfq_io_set_weight_legacy(of_css(of), NULL, weight);
}

static int bfqg_print_stat(struct seq_file *sf, void *v)
{
        blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), blkg_prfill_stat,
                          &blkcg_policy_bfq, seq_cft(sf)->private, false);
        return 0;
}

static int bfqg_print_rwstat(struct seq_file *sf, void *v)
{
        blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), blkg_prfill_rwstat,
                          &blkcg_policy_bfq, seq_cft(sf)->private, true);
        return 0;
}

static u64 bfqg_prfill_stat_recursive(struct seq_file *sf,
                                      struct blkg_policy_data *pd, int off)
{
        u64 sum = blkg_stat_recursive_sum(pd_to_blkg(pd),
                                          &blkcg_policy_bfq, off);
        return __blkg_prfill_u64(sf, pd, sum);
}

static u64 bfqg_prfill_rwstat_recursive(struct seq_file *sf,
                                        struct blkg_policy_data *pd, int off)
{
        struct blkg_rwstat sum = blkg_rwstat_recursive_sum(pd_to_blkg(pd),
                                                           &blkcg_policy_bfq,
                                                           off);
        return __blkg_prfill_rwstat(sf, pd, &sum);
}

static int bfqg_print_stat_recursive(struct seq_file *sf, void *v)
{
        blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
                          bfqg_prfill_stat_recursive, &blkcg_policy_bfq,
                          seq_cft(sf)->private, false);
        return 0;
}

static int bfqg_print_rwstat_recursive(struct seq_file *sf, void *v)
{
        blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
                          bfqg_prfill_rwstat_recursive, &blkcg_policy_bfq,
                          seq_cft(sf)->private, true);
        return 0;
}

static u64 bfqg_prfill_sectors(struct seq_file *sf, struct blkg_policy_data *pd,
                               int off)
{
        u64 sum = blkg_rwstat_total(&pd->blkg->stat_bytes);

        return __blkg_prfill_u64(sf, pd, sum >> 9);
}

static int bfqg_print_stat_sectors(struct seq_file *sf, void *v)
{
        blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
                          bfqg_prfill_sectors, &blkcg_policy_bfq, 0, false);
        return 0;
}

static u64 bfqg_prfill_sectors_recursive(struct seq_file *sf,
                                         struct blkg_policy_data *pd, int off)
{
        struct blkg_rwstat tmp = blkg_rwstat_recursive_sum(pd->blkg, NULL,
                                        offsetof(struct blkcg_gq, stat_bytes));
        u64 sum = atomic64_read(&tmp.aux_cnt[BLKG_RWSTAT_READ]) +
                atomic64_read(&tmp.aux_cnt[BLKG_RWSTAT_WRITE]);

        return __blkg_prfill_u64(sf, pd, sum >> 9);
}

static int bfqg_print_stat_sectors_recursive(struct seq_file *sf, void *v)
{
        blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
                          bfqg_prfill_sectors_recursive, &blkcg_policy_bfq, 0,
                          false);
        return 0;
}

static u64 bfqg_prfill_avg_queue_size(struct seq_file *sf,
                                      struct blkg_policy_data *pd, int off)
{
        struct bfq_group *bfqg = pd_to_bfqg(pd);
        u64 samples = blkg_stat_read(&bfqg->stats.avg_queue_size_samples);
        u64 v = 0;

        if (samples) {
                v = blkg_stat_read(&bfqg->stats.avg_queue_size_sum);
                v = div64_u64(v, samples);
        }
        __blkg_prfill_u64(sf, pd, v);
        return 0;
}

/* print avg_queue_size */
static int bfqg_print_avg_queue_size(struct seq_file *sf, void *v)
{
        blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
                          bfqg_prfill_avg_queue_size, &blkcg_policy_bfq,
                          0, false);
        return 0;
}

static struct bfq_group *
bfq_create_group_hierarchy(struct bfq_data *bfqd, int node)
{
        int ret;

        ret = blkcg_activate_policy(bfqd->queue, &blkcg_policy_bfq);
        if (ret)
                return NULL;

        return blkg_to_bfqg(bfqd->queue->root_blkg);
}

static struct cftype bfq_blkcg_legacy_files[] = {
        {
                .name = "bfq.weight",
                .flags = CFTYPE_NOT_ON_ROOT,
                .seq_show = bfq_io_show_weight,
                .write_u64 = bfq_io_set_weight_legacy,
        },

        /* statistics, covers only the tasks in the bfqg */
        {
                .name = "bfq.time",
                .private = offsetof(struct bfq_group, stats.time),
                .seq_show = bfqg_print_stat,
        },
        {
                .name = "bfq.sectors",
                .seq_show = bfqg_print_stat_sectors,
        },
        {
                .name = "bfq.io_service_bytes",
                .private = (unsigned long)&blkcg_policy_bfq,
                .seq_show = blkg_print_stat_bytes,
        },
        {
                .name = "bfq.io_serviced",
                .private = (unsigned long)&blkcg_policy_bfq,
                .seq_show = blkg_print_stat_ios,
        },
        {
                .name = "bfq.io_service_time",
                .private = offsetof(struct bfq_group, stats.service_time),
                .seq_show = bfqg_print_rwstat,
        },
        {
                .name = "bfq.io_wait_time",
                .private = offsetof(struct bfq_group, stats.wait_time),
                .seq_show = bfqg_print_rwstat,
        },
        {
                .name = "bfq.io_merged",
                .private = offsetof(struct bfq_group, stats.merged),
                .seq_show = bfqg_print_rwstat,
        },
        {
                .name = "bfq.io_queued",
                .private = offsetof(struct bfq_group, stats.queued),
                .seq_show = bfqg_print_rwstat,
        },

        /* the same statictics which cover the bfqg and its descendants */
        {
                .name = "bfq.time_recursive",
                .private = offsetof(struct bfq_group, stats.time),
                .seq_show = bfqg_print_stat_recursive,
        },
        {
                .name = "bfq.sectors_recursive",
                .seq_show = bfqg_print_stat_sectors_recursive,
        },
        {
                .name = "bfq.io_service_bytes_recursive",
                .private = (unsigned long)&blkcg_policy_bfq,
                .seq_show = blkg_print_stat_bytes_recursive,
        },
        {
                .name = "bfq.io_serviced_recursive",
                .private = (unsigned long)&blkcg_policy_bfq,
                .seq_show = blkg_print_stat_ios_recursive,
        },
        {
                .name = "bfq.io_service_time_recursive",
                .private = offsetof(struct bfq_group, stats.service_time),
                .seq_show = bfqg_print_rwstat_recursive,
        },
        {
                .name = "bfq.io_wait_time_recursive",
                .private = offsetof(struct bfq_group, stats.wait_time),
                .seq_show = bfqg_print_rwstat_recursive,
        },
        {
                .name = "bfq.io_merged_recursive",
                .private = offsetof(struct bfq_group, stats.merged),
                .seq_show = bfqg_print_rwstat_recursive,
        },
        {
                .name = "bfq.io_queued_recursive",
                .private = offsetof(struct bfq_group, stats.queued),
                .seq_show = bfqg_print_rwstat_recursive,
        },
        {
                .name = "bfq.avg_queue_size",
                .seq_show = bfqg_print_avg_queue_size,
        },
        {
                .name = "bfq.group_wait_time",
                .private = offsetof(struct bfq_group, stats.group_wait_time),
                .seq_show = bfqg_print_stat,
        },
        {
                .name = "bfq.idle_time",
                .private = offsetof(struct bfq_group, stats.idle_time),
                .seq_show = bfqg_print_stat,
        },
        {
                .name = "bfq.empty_time",
                .private = offsetof(struct bfq_group, stats.empty_time),
                .seq_show = bfqg_print_stat,
        },
        {
                .name = "bfq.dequeue",
                .private = offsetof(struct bfq_group, stats.dequeue),
                .seq_show = bfqg_print_stat,
        },
        { }     /* terminate */
};

static struct cftype bfq_blkg_files[] = {
        {
                .name = "bfq.weight",
                .flags = CFTYPE_NOT_ON_ROOT,
                .seq_show = bfq_io_show_weight,
                .write = bfq_io_set_weight,
        },
        {} /* terminate */
};

#else   /* CONFIG_BFQ_GROUP_IOSCHED */

static inline void bfqg_stats_update_io_add(struct bfq_group *bfqg,
                        struct bfq_queue *bfqq, unsigned int op) { }
static inline void
bfqg_stats_update_io_remove(struct bfq_group *bfqg, unsigned int op) { }
static inline void
bfqg_stats_update_io_merged(struct bfq_group *bfqg, unsigned int op) { }
static inline void bfqg_stats_update_completion(struct bfq_group *bfqg,
                        uint64_t start_time, uint64_t io_start_time,
                        unsigned int op) { }
static inline void
bfqg_stats_set_start_group_wait_time(struct bfq_group *bfqg,
                                     struct bfq_group *curr_bfqg) { }
static inline void bfqg_stats_end_empty_time(struct bfqg_stats *stats) { }
static inline void bfqg_stats_update_dequeue(struct bfq_group *bfqg) { }
static inline void bfqg_stats_set_start_empty_time(struct bfq_group *bfqg) { }
static inline void bfqg_stats_update_idle_time(struct bfq_group *bfqg) { }
static inline void bfqg_stats_set_start_idle_time(struct bfq_group *bfqg) { }
static inline void bfqg_stats_update_avg_queue_size(struct bfq_group *bfqg) { }

static void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq,
                          struct bfq_group *bfqg) {}

static void bfq_init_entity(struct bfq_entity *entity,
                            struct bfq_group *bfqg)
{
        struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);

        entity->weight = entity->new_weight;
        entity->orig_weight = entity->new_weight;
        if (bfqq) {
                bfqq->ioprio = bfqq->new_ioprio;
                bfqq->ioprio_class = bfqq->new_ioprio_class;
        }
        entity->sched_data = &bfqg->sched_data;
}

static void bfq_bic_update_cgroup(struct bfq_io_cq *bic, struct bio *bio) {}

static struct bfq_group *bfq_find_set_group(struct bfq_data *bfqd,
                                            struct blkcg *blkcg)
{
        return bfqd->root_group;
}

static struct bfq_group *bfqq_group(struct bfq_queue *bfqq)
{
        return bfqq->bfqd->root_group;
}

static struct bfq_group *bfq_create_group_hierarchy(struct bfq_data *bfqd,
                                                    int node)
{
        struct bfq_group *bfqg;
        int i;

        bfqg = kmalloc_node(sizeof(*bfqg), GFP_KERNEL | __GFP_ZERO, node);
        if (!bfqg)
                return NULL;

        for (i = 0; i < BFQ_IOPRIO_CLASSES; i++)
                bfqg->sched_data.service_tree[i] = BFQ_SERVICE_TREE_INIT;

        return bfqg;
}
#endif  /* CONFIG_BFQ_GROUP_IOSCHED */

#define bfq_class_idle(bfqq)    ((bfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
#define bfq_class_rt(bfqq)      ((bfqq)->ioprio_class == IOPRIO_CLASS_RT)

#define bfq_sample_valid(samples)       ((samples) > 80)

/*
 * Lifted from AS - choose which of rq1 and rq2 that is best served now.
 * We choose the request that is closesr to the head right now.  Distance
 * behind the head is penalized and only allowed to a certain extent.
 */
static struct request *bfq_choose_req(struct bfq_data *bfqd,
                                      struct request *rq1,
                                      struct request *rq2,
                                      sector_t last)
{
        sector_t s1, s2, d1 = 0, d2 = 0;
        unsigned long back_max;
#define BFQ_RQ1_WRAP    0x01 /* request 1 wraps */
#define BFQ_RQ2_WRAP    0x02 /* request 2 wraps */
        unsigned int wrap = 0; /* bit mask: requests behind the disk head? */

        if (!rq1 || rq1 == rq2)
                return rq2;
        if (!rq2)
                return rq1;

        if (rq_is_sync(rq1) && !rq_is_sync(rq2))
                return rq1;
        else if (rq_is_sync(rq2) && !rq_is_sync(rq1))
                return rq2;
        if ((rq1->cmd_flags & REQ_META) && !(rq2->cmd_flags & REQ_META))
                return rq1;
        else if ((rq2->cmd_flags & REQ_META) && !(rq1->cmd_flags & REQ_META))
                return rq2;

        s1 = blk_rq_pos(rq1);
        s2 = blk_rq_pos(rq2);

        /*
         * By definition, 1KiB is 2 sectors.
         */
        back_max = bfqd->bfq_back_max * 2;

        /*
         * Strict one way elevator _except_ in the case where we allow
         * short backward seeks which are biased as twice the cost of a
         * similar forward seek.
         */
        if (s1 >= last)
                d1 = s1 - last;
        else if (s1 + back_max >= last)
                d1 = (last - s1) * bfqd->bfq_back_penalty;
        else
                wrap |= BFQ_RQ1_WRAP;

        if (s2 >= last)
                d2 = s2 - last;
        else if (s2 + back_max >= last)
                d2 = (last - s2) * bfqd->bfq_back_penalty;
        else
                wrap |= BFQ_RQ2_WRAP;

        /* Found required data */

        /*
         * By doing switch() on the bit mask "wrap" we avoid having to
         * check two variables for all permutations: --> faster!
         */
        switch (wrap) {
        case 0: /* common case for CFQ: rq1 and rq2 not wrapped */
                if (d1 < d2)
                        return rq1;
                else if (d2 < d1)
                        return rq2;

                if (s1 >= s2)
                        return rq1;
                else
                        return rq2;

        case BFQ_RQ2_WRAP:
                return rq1;
        case BFQ_RQ1_WRAP:
                return rq2;
        case BFQ_RQ1_WRAP|BFQ_RQ2_WRAP: /* both rqs wrapped */
        default:
                /*
                 * Since both rqs are wrapped,
                 * start with the one that's further behind head
                 * (--> only *one* back seek required),
                 * since back seek takes more time than forward.
                 */
                if (s1 <= s2)
                        return rq1;
                else
                        return rq2;
        }
}

/*
 * Return expired entry, or NULL to just start from scratch in rbtree.
 */
static struct request *bfq_check_fifo(struct bfq_queue *bfqq,
                                      struct request *last)
{
        struct request *rq;

        if (bfq_bfqq_fifo_expire(bfqq))
                return NULL;

        bfq_mark_bfqq_fifo_expire(bfqq);

        rq = rq_entry_fifo(bfqq->fifo.next);

        if (rq == last || ktime_get_ns() < rq->fifo_time)
                return NULL;

        bfq_log_bfqq(bfqq->bfqd, bfqq, "check_fifo: returned %p", rq);
        return rq;
}

static struct request *bfq_find_next_rq(struct bfq_data *bfqd,
                                        struct bfq_queue *bfqq,
                                        struct request *last)
{
        struct rb_node *rbnext = rb_next(&last->rb_node);
        struct rb_node *rbprev = rb_prev(&last->rb_node);
        struct request *next, *prev = NULL;

        /* Follow expired path, else get first next available. */
        next = bfq_check_fifo(bfqq, last);
        if (next)
                return next;

        if (rbprev)
                prev = rb_entry_rq(rbprev);

        if (rbnext)
                next = rb_entry_rq(rbnext);
        else {
                rbnext = rb_first(&bfqq->sort_list);
                if (rbnext && rbnext != &last->rb_node)
                        next = rb_entry_rq(rbnext);
        }

        return bfq_choose_req(bfqd, next, prev, blk_rq_pos(last));
}

/* see the definition of bfq_async_charge_factor for details */
static unsigned long bfq_serv_to_charge(struct request *rq,
                                        struct bfq_queue *bfqq)
{
        if (bfq_bfqq_sync(bfqq))
                return blk_rq_sectors(rq);

        return blk_rq_sectors(rq) * bfq_async_charge_factor;
}

/**
 * bfq_updated_next_req - update the queue after a new next_rq selection.
 * @bfqd: the device data the queue belongs to.
 * @bfqq: the queue to update.
 *
 * If the first request of a queue changes we make sure that the queue
 * has enough budget to serve at least its first request (if the
 * request has grown).  We do this because if the queue has not enough
 * budget for its first request, it has to go through two dispatch
 * rounds to actually get it dispatched.
 */
static void bfq_updated_next_req(struct bfq_data *bfqd,
                                 struct bfq_queue *bfqq)
{
        struct bfq_entity *entity = &bfqq->entity;
        struct request *next_rq = bfqq->next_rq;
        unsigned long new_budget;

        if (!next_rq)
                return;

        if (bfqq == bfqd->in_service_queue)
                /*
                 * In order not to break guarantees, budgets cannot be
                 * changed after an entity has been selected.
                 */
                return;

        new_budget = max_t(unsigned long, bfqq->max_budget,
                           bfq_serv_to_charge(next_rq, bfqq));
        if (entity->budget != new_budget) {
                entity->budget = new_budget;
                bfq_log_bfqq(bfqd, bfqq, "updated next rq: new budget %lu",
                                         new_budget);
                bfq_requeue_bfqq(bfqd, bfqq);
        }
}

static int bfq_bfqq_budget_left(struct bfq_queue *bfqq)
{
        struct bfq_entity *entity = &bfqq->entity;

        return entity->budget - entity->service;
}

/*
 * If enough samples have been computed, return the current max budget
 * stored in bfqd, which is dynamically updated according to the
 * estimated disk peak rate; otherwise return the default max budget
 */
static int bfq_max_budget(struct bfq_data *bfqd)
{
        if (bfqd->budgets_assigned < bfq_stats_min_budgets)
                return bfq_default_max_budget;
        else
                return bfqd->bfq_max_budget;
}

/*
 * Return min budget, which is a fraction of the current or default
 * max budget (trying with 1/32)
 */
static int bfq_min_budget(struct bfq_data *bfqd)
{
        if (bfqd->budgets_assigned < bfq_stats_min_budgets)
                return bfq_default_max_budget / 32;
        else
                return bfqd->bfq_max_budget / 32;
}

static void bfq_bfqq_expire(struct bfq_data *bfqd,
                            struct bfq_queue *bfqq,
                            bool compensate,
                            enum bfqq_expiration reason);

/*
 * The next function, invoked after the input queue bfqq switches from
 * idle to busy, updates the budget of bfqq. The function also tells
 * whether the in-service queue should be expired, by returning
 * true. The purpose of expiring the in-service queue is to give bfqq
 * the chance to possibly preempt the in-service queue, and the reason
 * for preempting the in-service queue is to achieve the following
 * goal: guarantee to bfqq its reserved bandwidth even if bfqq has
 * expired because it has remained idle.
 *
 * In particular, bfqq may have expired for one of the following two
 * reasons:
 *
 * - BFQQE_NO_MORE_REQUESTS bfqq did not enjoy any device idling
 *   and did not make it to issue a new request before its last
 *   request was served;
 *
 * - BFQQE_TOO_IDLE bfqq did enjoy device idling, but did not issue
 *   a new request before the expiration of the idling-time.
 *
 * Even if bfqq has expired for one of the above reasons, the process
 * associated with the queue may be however issuing requests greedily,
 * and thus be sensitive to the bandwidth it receives (bfqq may have
 * remained idle for other reasons: CPU high load, bfqq not enjoying
 * idling, I/O throttling somewhere in the path from the process to
 * the I/O scheduler, ...). But if, after every expiration for one of
 * the above two reasons, bfqq has to wait for the service of at least
 * one full budget of another queue before being served again, then
 * bfqq is likely to get a much lower bandwidth or resource time than
 * its reserved ones. To address this issue, two countermeasures need
 * to be taken.
 *
 * First, the budget and the timestamps of bfqq need to be updated in
 * a special way on bfqq reactivation: they need to be updated as if
 * bfqq did not remain idle and did not expire. In fact, if they are
 * computed as if bfqq expired and remained idle until reactivation,
 * then the process associated with bfqq is treated as if, instead of
 * being greedy, it stopped issuing requests when bfqq remained idle,
 * and restarts issuing requests only on this reactivation. In other
 * words, the scheduler does not help the process recover the "service
 * hole" between bfqq expiration and reactivation. As a consequence,
 * the process receives a lower bandwidth than its reserved one. In
 * contrast, to recover this hole, the budget must be updated as if
 * bfqq was not expired at all before this reactivation, i.e., it must
 * be set to the value of the remaining budget when bfqq was
 * expired. Along the same line, timestamps need to be assigned the
 * value they had the last time bfqq was selected for service, i.e.,
 * before last expiration. Thus timestamps need to be back-shifted
 * with respect to their normal computation (see [1] for more details
 * on this tricky aspect).
 *
 * Secondly, to allow the process to recover the hole, the in-service
 * queue must be expired too, to give bfqq the chance to preempt it
 * immediately. In fact, if bfqq has to wait for a full budget of the
 * in-service queue to be completed, then it may become impossible to
 * let the process recover the hole, even if the back-shifted
 * timestamps of bfqq are lower than those of the in-service queue. If
 * this happens for most or all of the holes, then the process may not
 * receive its reserved bandwidth. In this respect, it is worth noting
 * that, being the service of outstanding requests unpreemptible, a
 * little fraction of the holes may however be unrecoverable, thereby
 * causing a little loss of bandwidth.
 *
 * The last important point is detecting whether bfqq does need this
 * bandwidth recovery. In this respect, the next function deems the
 * process associated with bfqq greedy, and thus allows it to recover
 * the hole, if: 1) the process is waiting for the arrival of a new
 * request (which implies that bfqq expired for one of the above two
 * reasons), and 2) such a request has arrived soon. The first
 * condition is controlled through the flag non_blocking_wait_rq,
 * while the second through the flag arrived_in_time. If both
 * conditions hold, then the function computes the budget in the
 * above-described special way, and signals that the in-service queue
 * should be expired. Timestamp back-shifting is done later in
 * __bfq_activate_entity.
 */
static bool bfq_bfqq_update_budg_for_activation(struct bfq_data *bfqd,
                                                struct bfq_queue *bfqq,
                                                bool arrived_in_time)
{
        struct bfq_entity *entity = &bfqq->entity;

        if (bfq_bfqq_non_blocking_wait_rq(bfqq) && arrived_in_time) {
                /*
                 * We do not clear the flag non_blocking_wait_rq here, as
                 * the latter is used in bfq_activate_bfqq to signal
                 * that timestamps need to be back-shifted (and is
                 * cleared right after).
                 */

                /*
                 * In next assignment we rely on that either
                 * entity->service or entity->budget are not updated
                 * on expiration if bfqq is empty (see
                 * __bfq_bfqq_recalc_budget). Thus both quantities
                 * remain unchanged after such an expiration, and the
                 * following statement therefore assigns to
                 * entity->budget the remaining budget on such an
                 * expiration. For clarity, entity->service is not
                 * updated on expiration in any case, and, in normal
                 * operation, is reset only when bfqq is selected for
                 * service (see bfq_get_next_queue).
                 */
                entity->budget = min_t(unsigned long,
                                       bfq_bfqq_budget_left(bfqq),
                                       bfqq->max_budget);

                return true;
        }

        entity->budget = max_t(unsigned long, bfqq->max_budget,
                               bfq_serv_to_charge(bfqq->next_rq, bfqq));
        bfq_clear_bfqq_non_blocking_wait_rq(bfqq);
        return false;
}

static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
                                             struct bfq_queue *bfqq,
                                             struct request *rq)
{
        bool bfqq_wants_to_preempt,
                /*
                 * See the comments on
                 * bfq_bfqq_update_budg_for_activation for
                 * details on the usage of the next variable.
                 */
                arrived_in_time =  ktime_get_ns() <=
                        bfqq->ttime.last_end_request +
                        bfqd->bfq_slice_idle * 3;

        bfqg_stats_update_io_add(bfqq_group(RQ_BFQQ(rq)), bfqq, rq->cmd_flags);

        /*
         * Update budget and check whether bfqq may want to preempt
         * the in-service queue.
         */
        bfqq_wants_to_preempt =
                bfq_bfqq_update_budg_for_activation(bfqd, bfqq,
                                                    arrived_in_time);

        if (!bfq_bfqq_IO_bound(bfqq)) {
                if (arrived_in_time) {
                        bfqq->requests_within_timer++;
                        if (bfqq->requests_within_timer >=
                            bfqd->bfq_requests_within_timer)
                                bfq_mark_bfqq_IO_bound(bfqq);
                } else
                        bfqq->requests_within_timer = 0;
        }

        bfq_add_bfqq_busy(bfqd, bfqq);

        /*
         * Expire in-service queue only if preemption may be needed
         * for guarantees. In this respect, the function
         * next_queue_may_preempt just checks a simple, necessary
         * condition, and not a sufficient condition based on
         * timestamps. In fact, for the latter condition to be
         * evaluated, timestamps would need first to be updated, and
         * this operation is quite costly (see the comments on the
         * function bfq_bfqq_update_budg_for_activation).
         */
        if (bfqd->in_service_queue && bfqq_wants_to_preempt &&
            next_queue_may_preempt(bfqd))
                bfq_bfqq_expire(bfqd, bfqd->in_service_queue,
                                false, BFQQE_PREEMPTED);
}

static void bfq_add_request(struct request *rq)
{
        struct bfq_queue *bfqq = RQ_BFQQ(rq);
        struct bfq_data *bfqd = bfqq->bfqd;
        struct request *next_rq, *prev;

        bfq_log_bfqq(bfqd, bfqq, "add_request %d", rq_is_sync(rq));
        bfqq->queued[rq_is_sync(rq)]++;
        bfqd->queued++;

        elv_rb_add(&bfqq->sort_list, rq);

        /*
         * Check if this request is a better next-serve candidate.
         */
        prev = bfqq->next_rq;
        next_rq = bfq_choose_req(bfqd, bfqq->next_rq, rq, bfqd->last_position);
        bfqq->next_rq = next_rq;

        if (!bfq_bfqq_busy(bfqq)) /* switching to busy ... */
                bfq_bfqq_handle_idle_busy_switch(bfqd, bfqq, rq);
        else if (prev != bfqq->next_rq)
                bfq_updated_next_req(bfqd, bfqq);
}

static struct request *bfq_find_rq_fmerge(struct bfq_data *bfqd,
                                          struct bio *bio,
                                          struct request_queue *q)
{
        struct bfq_queue *bfqq = bfqd->bio_bfqq;


        if (bfqq)
                return elv_rb_find(&bfqq->sort_list, bio_end_sector(bio));

        return NULL;
}

static sector_t get_sdist(sector_t last_pos, struct request *rq)
{
        if (last_pos)
                return abs(blk_rq_pos(rq) - last_pos);

        return 0;
}

#if 0 /* Still not clear if we can do without next two functions */
static void bfq_activate_request(struct request_queue *q, struct request *rq)
{
        struct bfq_data *bfqd = q->elevator->elevator_data;

        bfqd->rq_in_driver++;
}

static void bfq_deactivate_request(struct request_queue *q, struct request *rq)
{
        struct bfq_data *bfqd = q->elevator->elevator_data;

        bfqd->rq_in_driver--;
}
#endif

static void bfq_remove_request(struct request_queue *q,
                               struct request *rq)
{
        struct bfq_queue *bfqq = RQ_BFQQ(rq);
        struct bfq_data *bfqd = bfqq->bfqd;
        const int sync = rq_is_sync(rq);

        if (bfqq->next_rq == rq) {
                bfqq->next_rq = bfq_find_next_rq(bfqd, bfqq, rq);
                bfq_updated_next_req(bfqd, bfqq);
        }

        if (rq->queuelist.prev != &rq->queuelist)
                list_del_init(&rq->queuelist);
        bfqq->queued[sync]--;
        bfqd->queued--;
        elv_rb_del(&bfqq->sort_list, rq);

        elv_rqhash_del(q, rq);
        if (q->last_merge == rq)
                q->last_merge = NULL;

        if (RB_EMPTY_ROOT(&bfqq->sort_list)) {
                bfqq->next_rq = NULL;

                if (bfq_bfqq_busy(bfqq) && bfqq != bfqd->in_service_queue) {
                        bfq_del_bfqq_busy(bfqd, bfqq, false);
                        /*
                         * bfqq emptied. In normal operation, when
                         * bfqq is empty, bfqq->entity.service and
                         * bfqq->entity.budget must contain,
                         * respectively, the service received and the
                         * budget used last time bfqq emptied. These
                         * facts do not hold in this case, as at least
                         * this last removal occurred while bfqq is
                         * not in service. To avoid inconsistencies,
                         * reset both bfqq->entity.service and
                         * bfqq->entity.budget, if bfqq has still a
                         * process that may issue I/O requests to it.
                         */
                        bfqq->entity.budget = bfqq->entity.service = 0;
                }
        }

        if (rq->cmd_flags & REQ_META)
                bfqq->meta_pending--;

        bfqg_stats_update_io_remove(bfqq_group(bfqq), rq->cmd_flags);
}

static bool bfq_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio)
{
        struct request_queue *q = hctx->queue;
        struct bfq_data *bfqd = q->elevator->elevator_data;
        struct request *free = NULL;
        /*
         * bfq_bic_lookup grabs the queue_lock: invoke it now and
         * store its return value for later use, to avoid nesting
         * queue_lock inside the bfqd->lock. We assume that the bic
         * returned by bfq_bic_lookup does not go away before
         * bfqd->lock is taken.
         */
        struct bfq_io_cq *bic = bfq_bic_lookup(bfqd, current->io_context, q);
        bool ret;

        spin_lock_irq(&bfqd->lock);

        if (bic)
                bfqd->bio_bfqq = bic_to_bfqq(bic, op_is_sync(bio->bi_opf));
        else
                bfqd->bio_bfqq = NULL;
        bfqd->bio_bic = bic;

        ret = blk_mq_sched_try_merge(q, bio, &free);

        if (free)
                blk_mq_free_request(free);
        spin_unlock_irq(&bfqd->lock);

        return ret;
}

static int bfq_request_merge(struct request_queue *q, struct request **req,
                             struct bio *bio)
{
        struct bfq_data *bfqd = q->elevator->elevator_data;
        struct request *__rq;

        __rq = bfq_find_rq_fmerge(bfqd, bio, q);
        if (__rq && elv_bio_merge_ok(__rq, bio)) {
                *req = __rq;
                return ELEVATOR_FRONT_MERGE;
        }

        return ELEVATOR_NO_MERGE;
}

static void bfq_request_merged(struct request_queue *q, struct request *req,
                               enum elv_merge type)
{
        if (type == ELEVATOR_FRONT_MERGE &&
            rb_prev(&req->rb_node) &&
            blk_rq_pos(req) <
            blk_rq_pos(container_of(rb_prev(&req->rb_node),
                                    struct request, rb_node))) {
                struct bfq_queue *bfqq = RQ_BFQQ(req);
                struct bfq_data *bfqd = bfqq->bfqd;
                struct request *prev, *next_rq;

                /* Reposition request in its sort_list */
                elv_rb_del(&bfqq->sort_list, req);
                elv_rb_add(&bfqq->sort_list, req);

                /* Choose next request to be served for bfqq */
                prev = bfqq->next_rq;
                next_rq = bfq_choose_req(bfqd, bfqq->next_rq, req,
                                         bfqd->last_position);
                bfqq->next_rq = next_rq;
                /*
                 * If next_rq changes, update the queue's budget to fit
                 * the new request.
                 */
                if (prev != bfqq->next_rq)
                        bfq_updated_next_req(bfqd, bfqq);
        }
}

static void bfq_requests_merged(struct request_queue *q, struct request *rq,
                                struct request *next)
{
        struct bfq_queue *bfqq = RQ_BFQQ(rq), *next_bfqq = RQ_BFQQ(next);

        if (!RB_EMPTY_NODE(&rq->rb_node))
                goto end;
        spin_lock_irq(&bfqq->bfqd->lock);

        /*
         * If next and rq belong to the same bfq_queue and next is older
         * than rq, then reposition rq in the fifo (by substituting next
         * with rq). Otherwise, if next and rq belong to different
         * bfq_queues, never reposition rq: in fact, we would have to
         * reposition it with respect to next's position in its own fifo,
         * which would most certainly be too expensive with respect to
         * the benefits.
         */
        if (bfqq == next_bfqq &&
            !list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
            next->fifo_time < rq->fifo_time) {
                list_del_init(&rq->queuelist);
                list_replace_init(&next->queuelist, &rq->queuelist);
                rq->fifo_time = next->fifo_time;
        }

        if (bfqq->next_rq == next)
                bfqq->next_rq = rq;

        bfq_remove_request(q, next);

        spin_unlock_irq(&bfqq->bfqd->lock);
end:
        bfqg_stats_update_io_merged(bfqq_group(bfqq), next->cmd_flags);
}

static bool bfq_allow_bio_merge(struct request_queue *q, struct request *rq,
                                struct bio *bio)
{
        struct bfq_data *bfqd = q->elevator->elevator_data;
        bool is_sync = op_is_sync(bio->bi_opf);
        struct bfq_queue *bfqq = bfqd->bio_bfqq;

        /*
         * Disallow merge of a sync bio into an async request.
         */
        if (is_sync && !rq_is_sync(rq))
                return false;

        /*
         * Lookup the bfqq that this bio will be queued with. Allow
         * merge only if rq is queued there.
         */
        if (!bfqq)
                return false;

        return bfqq == RQ_BFQQ(rq);
}

static void __bfq_set_in_service_queue(struct bfq_data *bfqd,
                                       struct bfq_queue *bfqq)
{
        if (bfqq) {
                bfqg_stats_update_avg_queue_size(bfqq_group(bfqq));
                bfq_mark_bfqq_budget_new(bfqq);
                bfq_clear_bfqq_fifo_expire(bfqq);

                bfqd->budgets_assigned = (bfqd->budgets_assigned * 7 + 256) / 8;

                bfq_log_bfqq(bfqd, bfqq,
                             "set_in_service_queue, cur-budget = %d",
                             bfqq->entity.budget);
        }

        bfqd->in_service_queue = bfqq;
}

/*
 * Get and set a new queue for service.
 */
static struct bfq_queue *bfq_set_in_service_queue(struct bfq_data *bfqd)
{
        struct bfq_queue *bfqq = bfq_get_next_queue(bfqd);

        __bfq_set_in_service_queue(bfqd, bfqq);
        return bfqq;
}

static void bfq_arm_slice_timer(struct bfq_data *bfqd)
{
        struct bfq_queue *bfqq = bfqd->in_service_queue;
        struct bfq_io_cq *bic;
        u32 sl;

        /* Processes have exited, don't wait. */
        bic = bfqd->in_service_bic;
        if (!bic || atomic_read(&bic->icq.ioc->active_ref) == 0)
                return;

        bfq_mark_bfqq_wait_request(bfqq);

        /*
         * We don't want to idle for seeks, but we do want to allow
         * fair distribution of slice time for a process doing back-to-back
         * seeks. So allow a little bit of time for him to submit a new rq.
         */
        sl = bfqd->bfq_slice_idle;
        /*
         * Grant only minimum idle time if the queue is seeky.
         */
        if (BFQQ_SEEKY(bfqq))
                sl = min_t(u64, sl, BFQ_MIN_TT);

        bfqd->last_idling_start = ktime_get();
        hrtimer_start(&bfqd->idle_slice_timer, ns_to_ktime(sl),
                      HRTIMER_MODE_REL);
        bfqg_stats_set_start_idle_time(bfqq_group(bfqq));
}

/*
 * Set the maximum time for the in-service queue to consume its
 * budget. This prevents seeky processes from lowering the disk
 * throughput (always guaranteed with a time slice scheme as in CFQ).
 */
static void bfq_set_budget_timeout(struct bfq_data *bfqd)
{
        struct bfq_queue *bfqq = bfqd->in_service_queue;
        unsigned int timeout_coeff = bfqq->entity.weight /
                                     bfqq->entity.orig_weight;

        bfqd->last_budget_start = ktime_get();

        bfq_clear_bfqq_budget_new(bfqq);
        bfqq->budget_timeout = jiffies +
                bfqd->bfq_timeout * timeout_coeff;

        bfq_log_bfqq(bfqd, bfqq, "set budget_timeout %u",
                jiffies_to_msecs(bfqd->bfq_timeout * timeout_coeff));
}

/*
 * In autotuning mode, max_budget is dynamically recomputed as the
 * amount of sectors transferred in timeout at the estimated peak
 * rate. This enables BFQ to utilize a full timeslice with a full
 * budget, even if the in-service queue is served at peak rate. And
 * this maximises throughput with sequential workloads.
 */
static unsigned long bfq_calc_max_budget(struct bfq_data *bfqd)
{
        return (u64)bfqd->peak_rate * USEC_PER_MSEC *
                jiffies_to_msecs(bfqd->bfq_timeout)>>BFQ_RATE_SHIFT;
}

static void bfq_reset_rate_computation(struct bfq_data *bfqd,
                                       struct request *rq)
{
        if (rq != NULL) { /* new rq dispatch now, reset accordingly */
                bfqd->last_dispatch = bfqd->first_dispatch = ktime_get_ns();
                bfqd->peak_rate_samples = 1;
                bfqd->sequential_samples = 0;
                bfqd->tot_sectors_dispatched = bfqd->last_rq_max_size =
                        blk_rq_sectors(rq);
        } else /* no new rq dispatched, just reset the number of samples */
                bfqd->peak_rate_samples = 0; /* full re-init on next disp. */

        bfq_log(bfqd,
                "reset_rate_computation at end, sample %u/%u tot_sects %llu",
                bfqd->peak_rate_samples, bfqd->sequential_samples,
                bfqd->tot_sectors_dispatched);
}

static void bfq_update_rate_reset(struct bfq_data *bfqd, struct request *rq)
{
        u32 rate, weight, divisor;

        /*
         * For the convergence property to hold (see comments on
         * bfq_update_peak_rate()) and for the assessment to be
         * reliable, a minimum number of samples must be present, and
         * a minimum amount of time must have elapsed. If not so, do
         * not compute new rate. Just reset parameters, to get ready
         * for a new evaluation attempt.
         */
        if (bfqd->peak_rate_samples < BFQ_RATE_MIN_SAMPLES ||
            bfqd->delta_from_first < BFQ_RATE_MIN_INTERVAL)
                goto reset_computation;

        /*
         * If a new request completion has occurred after last
         * dispatch, then, to approximate the rate at which requests
         * have been served by the device, it is more precise to
         * extend the observation interval to the last completion.
         */
        bfqd->delta_from_first =
                max_t(u64, bfqd->delta_from_first,
                      bfqd->last_completion - bfqd->first_dispatch);

        /*
         * Rate computed in sects/usec, and not sects/nsec, for
         * precision issues.
         */
        rate = div64_ul(bfqd->tot_sectors_dispatched<<BFQ_RATE_SHIFT,
                        div_u64(bfqd->delta_from_first, NSEC_PER_USEC));

        /*
         * Peak rate not updated if:
         * - the percentage of sequential dispatches is below 3/4 of the
         *   total, and rate is below the current estimated peak rate
         * - rate is unreasonably high (> 20M sectors/sec)
         */
        if ((bfqd->sequential_samples < (3 * bfqd->peak_rate_samples)>>2 &&
             rate <= bfqd->peak_rate) ||
                rate > 20<<BFQ_RATE_SHIFT)
                goto reset_computation;

        /*
         * We have to update the peak rate, at last! To this purpose,
         * we use a low-pass filter. We compute the smoothing constant
         * of the filter as a function of the 'weight' of the new
         * measured rate.
         *
         * As can be seen in next formulas, we define this weight as a
         * quantity proportional to how sequential the workload is,
         * and to how long the observation time interval is.
         *
         * The weight runs from 0 to 8. The maximum value of the
         * weight, 8, yields the minimum value for the smoothing
         * constant. At this minimum value for the smoothing constant,
         * the measured rate contributes for half of the next value of
         * the estimated peak rate.
         *
         * So, the first step is to compute the weight as a function
         * of how sequential the workload is. Note that the weight
         * cannot reach 9, because bfqd->sequential_samples cannot
         * become equal to bfqd->peak_rate_samples, which, in its
         * turn, holds true because bfqd->sequential_samples is not
         * incremented for the first sample.
         */
        weight = (9 * bfqd->sequential_samples) / bfqd->peak_rate_samples;

        /*
         * Second step: further refine the weight as a function of the
         * duration of the observation interval.
         */
        weight = min_t(u32, 8,
                       div_u64(weight * bfqd->delta_from_first,
                               BFQ_RATE_REF_INTERVAL));

        /*
         * Divisor ranging from 10, for minimum weight, to 2, for
         * maximum weight.
         */
        divisor = 10 - weight;

        /*
         * Finally, update peak rate:
         *
         * peak_rate = peak_rate * (divisor-1) / divisor  +  rate / divisor
         */
        bfqd->peak_rate *= divisor-1;
        bfqd->peak_rate /= divisor;
        rate /= divisor; /* smoothing constant alpha = 1/divisor */

        bfqd->peak_rate += rate;
        if (bfqd->bfq_user_max_budget == 0)
                bfqd->bfq_max_budget =
                        bfq_calc_max_budget(bfqd);

reset_computation:
        bfq_reset_rate_computation(bfqd, rq);
}

/*
 * Update the read/write peak rate (the main quantity used for
 * auto-tuning, see update_thr_responsiveness_params()).
 *
 * It is not trivial to estimate the peak rate (correctly): because of
 * the presence of sw and hw queues between the scheduler and the
 * device components that finally serve I/O requests, it is hard to
 * say exactly when a given dispatched request is served inside the
 * device, and for how long. As a consequence, it is hard to know
 * precisely at what rate a given set of requests is actually served
 * by the device.
 *
 * On the opposite end, the dispatch time of any request is trivially
 * available, and, from this piece of information, the "dispatch rate"
 * of requests can be immediately computed. So, the idea in the next
 * function is to use what is known, namely request dispatch times
 * (plus, when useful, request completion times), to estimate what is
 * unknown, namely in-device request service rate.
 *
 * The main issue is that, because of the above facts, the rate at
 * which a certain set of requests is dispatched over a certain time
 * interval can vary greatly with respect to the rate at which the
 * same requests are then served. But, since the size of any
 * intermediate queue is limited, and the service scheme is lossless
 * (no request is silently dropped), the following obvious convergence
 * property holds: the number of requests dispatched MUST become
 * closer and closer to the number of requests completed as the
 * observation interval grows. This is the key property used in
 * the next function to estimate the peak service rate as a function
 * of the observed dispatch rate. The function assumes to be invoked
 * on every request dispatch.
 */
static void bfq_update_peak_rate(struct bfq_data *bfqd, struct request *rq)
{
        u64 now_ns = ktime_get_ns();

        if (bfqd->peak_rate_samples == 0) { /* first dispatch */
                bfq_log(bfqd, "update_peak_rate: goto reset, samples %d",
                        bfqd->peak_rate_samples);
                bfq_reset_rate_computation(bfqd, rq);
                goto update_last_values; /* will add one sample */
        }

        /*
         * Device idle for very long: the observation interval lasting
         * up to this dispatch cannot be a valid observation interval
         * for computing a new peak rate (similarly to the late-
         * completion event in bfq_completed_request()). Go to
         * update_rate_and_reset to have the following three steps
         * taken:
         * - close the observation interval at the last (previous)
         *   request dispatch or completion
         * - compute rate, if possible, for that observation interval
         * - start a new observation interval with this dispatch
         */
        if (now_ns - bfqd->last_dispatch > 100*NSEC_PER_MSEC &&
            bfqd->rq_in_driver == 0)
                goto update_rate_and_reset;

        /* Update sampling information */
        bfqd->peak_rate_samples++;

        if ((bfqd->rq_in_driver > 0 ||
                now_ns - bfqd->last_completion < BFQ_MIN_TT)
             && get_sdist(bfqd->last_position, rq) < BFQQ_SEEK_THR)
                bfqd->sequential_samples++;

        bfqd->tot_sectors_dispatched += blk_rq_sectors(rq);

        /* Reset max observed rq size every 32 dispatches */
        if (likely(bfqd->peak_rate_samples % 32))
                bfqd->last_rq_max_size =
                        max_t(u32, blk_rq_sectors(rq), bfqd->last_rq_max_size);
        else
                bfqd->last_rq_max_size = blk_rq_sectors(rq);

        bfqd->delta_from_first = now_ns - bfqd->first_dispatch;

        /* Target observation interval not yet reached, go on sampling */
        if (bfqd->delta_from_first < BFQ_RATE_REF_INTERVAL)
                goto update_last_values;

update_rate_and_reset:
        bfq_update_rate_reset(bfqd, rq);
update_last_values:
        bfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
        bfqd->last_dispatch = now_ns;
}

/*
 * Remove request from internal lists.
 */
static void bfq_dispatch_remove(struct request_queue *q, struct request *rq)
{
        struct bfq_queue *bfqq = RQ_BFQQ(rq);

        /*
         * For consistency, the next instruction should have been
         * executed after removing the request from the queue and
         * dispatching it.  We execute instead this instruction before
         * bfq_remove_request() (and hence introduce a temporary
         * inconsistency), for efficiency.  In fact, should this
         * dispatch occur for a non in-service bfqq, this anticipated
         * increment prevents two counters related to bfqq->dispatched
         * from risking to be, first, uselessly decremented, and then
         * incremented again when the (new) value of bfqq->dispatched
         * happens to be taken into account.
         */
        bfqq->dispatched++;
        bfq_update_peak_rate(q->elevator->elevator_data, rq);

        bfq_remove_request(q, rq);
}

static void __bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq)
{
        if (RB_EMPTY_ROOT(&bfqq->sort_list))
                bfq_del_bfqq_busy(bfqd, bfqq, true);
        else
                bfq_requeue_bfqq(bfqd, bfqq);

        /*
         * All in-service entities must have been properly deactivated
         * or requeued before executing the next function, which
         * resets all in-service entites as no more in service.
         */
        __bfq_bfqd_reset_in_service(bfqd);
}

/**
 * __bfq_bfqq_recalc_budget - try to adapt the budget to the @bfqq behavior.
 * @bfqd: device data.
 * @bfqq: queue to update.
 * @reason: reason for expiration.
 *
 * Handle the feedback on @bfqq budget at queue expiration.
 * See the body for detailed comments.
 */
static void __bfq_bfqq_recalc_budget(struct bfq_data *bfqd,
                                     struct bfq_queue *bfqq,
                                     enum bfqq_expiration reason)
{
        struct request *next_rq;
        int budget, min_budget;

        budget = bfqq->max_budget;
        min_budget = bfq_min_budget(bfqd);

        bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last budg %d, budg left %d",
                bfqq->entity.budget, bfq_bfqq_budget_left(bfqq));
        bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last max_budg %d, min budg %d",
                budget, bfq_min_budget(bfqd));
        bfq_log_bfqq(bfqd, bfqq, "recalc_budg: sync %d, seeky %d",
                bfq_bfqq_sync(bfqq), BFQQ_SEEKY(bfqd->in_service_queue));

        if (bfq_bfqq_sync(bfqq)) {
                switch (reason) {
                /*
                 * Caveat: in all the following cases we trade latency
                 * for throughput.
                 */
                case BFQQE_TOO_IDLE:
                        /*
                         * This is the only case where we may reduce
                         * the budget: if there is no request of the
                         * process still waiting for completion, then
                         * we assume (tentatively) that the timer has
                         * expired because the batch of requests of
                         * the process could have been served with a
                         * smaller budget.  Hence, betting that
                         * process will behave in the same way when it
                         * becomes backlogged again, we reduce its
                         * next budget.  As long as we guess right,
                         * this budget cut reduces the latency
                         * experienced by the process.
                         *
                         * However, if there are still outstanding
                         * requests, then the process may have not yet
                         * issued its next request just because it is
                         * still waiting for the completion of some of
                         * the still outstanding ones.  So in this
                         * subcase we do not reduce its budget, on the
                         * contrary we increase it to possibly boost
                         * the throughput, as discussed in the
                         * comments to the BUDGET_TIMEOUT case.
                         */
                        if (bfqq->dispatched > 0) /* still outstanding reqs */
                                budget = min(budget * 2, bfqd->bfq_max_budget);
                        else {
                                if (budget > 5 * min_budget)
                                        budget -= 4 * min_budget;
                                else
                                        budget = min_budget;
                        }
                        break;
                case BFQQE_BUDGET_TIMEOUT:
                        /*
                         * We double the budget here because it gives
                         * the chance to boost the throughput if this
                         * is not a seeky process (and has bumped into
                         * this timeout because of, e.g., ZBR).
                         */
                        budget = min(budget * 2, bfqd->bfq_max_budget);
                        break;
                case BFQQE_BUDGET_EXHAUSTED:
                        /*
                         * The process still has backlog, and did not
                         * let either the budget timeout or the disk
                         * idling timeout expire. Hence it is not
                         * seeky, has a short thinktime and may be
                         * happy with a higher budget too. So
                         * definitely increase the budget of this good
                         * candidate to boost the disk throughput.
                         */
                        budget = min(budget * 4, bfqd->bfq_max_budget);
                        break;
                case BFQQE_NO_MORE_REQUESTS:
                        /*
                         * For queues that expire for this reason, it
                         * is particularly important to keep the
                         * budget close to the actual service they
                         * need. Doing so reduces the timestamp
                         * misalignment problem described in the
                         * comments in the body of
                         * __bfq_activate_entity. In fact, suppose
                         * that a queue systematically expires for
                         * BFQQE_NO_MORE_REQUESTS and presents a
                         * new request in time to enjoy timestamp
                         * back-shifting. The larger the budget of the
                         * queue is with respect to the service the
                         * queue actually requests in each service
                         * slot, the more times the queue can be
                         * reactivated with the same virtual finish
                         * time. It follows that, even if this finish
                         * time is pushed to the system virtual time
                         * to reduce the consequent timestamp
                         * misalignment, the queue unjustly enjoys for
                         * many re-activations a lower finish time
                         * than all newly activated queues.
                         *
                         * The service needed by bfqq is measured
                         * quite precisely by bfqq->entity.service.
                         * Since bfqq does not enjoy device idling,
                         * bfqq->entity.service is equal to the number
                         * of sectors that the process associated with
                         * bfqq requested to read/write before waiting
                         * for request completions, or blocking for
                         * other reasons.
                         */
                        budget = max_t(int, bfqq->entity.service, min_budget);
                        break;
                default:
                        return;
                }
        } else {
                /*
                 * Async queues get always the maximum possible
                 * budget, as for them we do not care about latency
                 * (in addition, their ability to dispatch is limited
                 * by the charging factor).
                 */
                budget = bfqd->bfq_max_budget;
        }

        bfqq->max_budget = budget;

        if (bfqd->budgets_assigned >= bfq_stats_min_budgets &&
            !bfqd->bfq_user_max_budget)
                bfqq->max_budget = min(bfqq->max_budget, bfqd->bfq_max_budget);

        /*
         * If there is still backlog, then assign a new budget, making
         * sure that it is large enough for the next request.  Since
         * the finish time of bfqq must be kept in sync with the
         * budget, be sure to call __bfq_bfqq_expire() *after* this
         * update.
         *
         * If there is no backlog, then no need to update the budget;
         * it will be updated on the arrival of a new request.
         */
        next_rq = bfqq->next_rq;
        if (next_rq)
                bfqq->entity.budget = max_t(unsigned long, bfqq->max_budget,
                                            bfq_serv_to_charge(next_rq, bfqq));

        bfq_log_bfqq(bfqd, bfqq, "head sect: %u, new budget %d",
                        next_rq ? blk_rq_sectors(next_rq) : 0,
                        bfqq->entity.budget);
}

/*
 * Return true if the process associated with bfqq is "slow". The slow
 * flag is used, in addition to the budget timeout, to reduce the
 * amount of service provided to seeky processes, and thus reduce
 * their chances to lower the throughput. More details in the comments
 * on the function bfq_bfqq_expire().
 *
 * An important observation is in order: as discussed in the comments
 * on the function bfq_update_peak_rate(), with devices with internal
 * queues, it is hard if ever possible to know when and for how long
 * an I/O request is processed by the device (apart from the trivial
 * I/O pattern where a new request is dispatched only after the
 * previous one has been completed). This makes it hard to evaluate
 * the real rate at which the I/O requests of each bfq_queue are
 * served.  In fact, for an I/O scheduler like BFQ, serving a
 * bfq_queue means just dispatching its requests during its service
 * slot (i.e., until the budget of the queue is exhausted, or the
 * queue remains idle, or, finally, a timeout fires). But, during the
 * service slot of a bfq_queue, around 100 ms at most, the device may
 * be even still processing requests of bfq_queues served in previous
 * service slots. On the opposite end, the requests of the in-service
 * bfq_queue may be completed after the service slot of the queue
 * finishes.
 *
 * Anyway, unless more sophisticated solutions are used
 * (where possible), the sum of the sizes of the requests dispatched
 * during the service slot of a bfq_queue is probably the only
 * approximation available for the service received by the bfq_queue
 * during its service slot. And this sum is the quantity used in this
 * function to evaluate the I/O speed of a process.
 */
static bool bfq_bfqq_is_slow(struct bfq_data *bfqd, struct bfq_queue *bfqq,
                                 bool compensate, enum bfqq_expiration reason,
                                 unsigned long *delta_ms)
{
        ktime_t delta_ktime;
        u32 delta_usecs;
        bool slow = BFQQ_SEEKY(bfqq); /* if delta too short, use seekyness */

        if (!bfq_bfqq_sync(bfqq))
                return false;

        if (compensate)
                delta_ktime = bfqd->last_idling_start;
        else
                delta_ktime = ktime_get();
        delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start);
        delta_usecs = ktime_to_us(delta_ktime);

        /* don't use too short time intervals */
        if (delta_usecs < 1000) {
                if (blk_queue_nonrot(bfqd->queue))
                         /*
                          * give same worst-case guarantees as idling
                          * for seeky
                          */
                        *delta_ms = BFQ_MIN_TT / NSEC_PER_MSEC;
                else /* charge at least one seek */
                        *delta_ms = bfq_slice_idle / NSEC_PER_MSEC;

                return slow;
        }

        *delta_ms = delta_usecs / USEC_PER_MSEC;

        /*
         * Use only long (> 20ms) intervals to filter out excessive
         * spikes in service rate estimation.
         */
        if (delta_usecs > 20000) {
                /*
                 * Caveat for rotational devices: processes doing I/O
                 * in the slower disk zones tend to be slow(er) even
                 * if not seeky. In this respect, the estimated peak
                 * rate is likely to be an average over the disk
                 * surface. Accordingly, to not be too harsh with
                 * unlucky processes, a process is deemed slow only if
                 * its rate has been lower than half of the estimated
                 * peak rate.
                 */
                slow = bfqq->entity.service < bfqd->bfq_max_budget / 2;
        }

        bfq_log_bfqq(bfqd, bfqq, "bfq_bfqq_is_slow: slow %d", slow);

        return slow;
}

/*
 * Return the farthest past time instant according to jiffies
 * macros.
 */
static unsigned long bfq_smallest_from_now(void)
{
        return jiffies - MAX_JIFFY_OFFSET;
}

/**
 * bfq_bfqq_expire - expire a queue.
 * @bfqd: device owning the queue.
 * @bfqq: the queue to expire.
 * @compensate: if true, compensate for the time spent idling.
 * @reason: the reason causing the expiration.
 *
 * If the process associated with bfqq does slow I/O (e.g., because it
 * issues random requests), we charge bfqq with the time it has been
 * in service instead of the service it has received (see
 * bfq_bfqq_charge_time for details on how this goal is achieved). As
 * a consequence, bfqq will typically get higher timestamps upon
 * reactivation, and hence it will be rescheduled as if it had
 * received more service than what it has actually received. In the
 * end, bfqq receives less service in proportion to how slowly its
 * associated process consumes its budgets (and hence how seriously it
 * tends to lower the throughput). In addition, this time-charging
 * strategy guarantees time fairness among slow processes. In
 * contrast, if the process associated with bfqq is not slow, we
 * charge bfqq exactly with the service it has received.
 *
 * Charging time to the first type of queues and the exact service to
 * the other has the effect of using the WF2Q+ policy to schedule the
 * former on a timeslice basis, without violating service domain
 * guarantees among the latter.
 */
static void bfq_bfqq_expire(struct bfq_data *bfqd,
                            struct bfq_queue *bfqq,
                            bool compensate,
                            enum bfqq_expiration reason)
{
        bool slow;
        unsigned long delta = 0;
        struct bfq_entity *entity = &bfqq->entity;
        int ref;

        /*
         * Check whether the process is slow (see bfq_bfqq_is_slow).
         */
        slow = bfq_bfqq_is_slow(bfqd, bfqq, compensate, reason, &delta);

        /*
         * As above explained, charge slow (typically seeky) and
         * timed-out queues with the time and not the service
         * received, to favor sequential workloads.
         *
         * Processes doing I/O in the slower disk zones will tend to
         * be slow(er) even if not seeky. Therefore, since the
         * estimated peak rate is actually an average over the disk
         * surface, these processes may timeout just for bad luck. To
         * avoid punishing them, do not charge time to processes that
         * succeeded in consuming at least 2/3 of their budget. This
         * allows BFQ to preserve enough elasticity to still perform
         * bandwidth, and not time, distribution with little unlucky
         * or quasi-sequential processes.
         */
        if (slow ||
            (reason == BFQQE_BUDGET_TIMEOUT &&
             bfq_bfqq_budget_left(bfqq) >=  entity->budget / 3))
                bfq_bfqq_charge_time(bfqd, bfqq, delta);

        if (reason == BFQQE_TOO_IDLE &&
            entity->service <= 2 * entity->budget / 10)
                bfq_clear_bfqq_IO_bound(bfqq);

        bfq_log_bfqq(bfqd, bfqq,
                "expire (%d, slow %d, num_disp %d, idle_win %d)", reason,
                slow, bfqq->dispatched, bfq_bfqq_idle_window(bfqq));

        /*
         * Increase, decrease or leave budget unchanged according to
         * reason.
         */
        __bfq_bfqq_recalc_budget(bfqd, bfqq, reason);
        ref = bfqq->ref;
        __bfq_bfqq_expire(bfqd, bfqq);

        /* mark bfqq as waiting a request only if a bic still points to it */
        if (ref > 1 && !bfq_bfqq_busy(bfqq) &&
            reason != BFQQE_BUDGET_TIMEOUT &&
            reason != BFQQE_BUDGET_EXHAUSTED)
                bfq_mark_bfqq_non_blocking_wait_rq(bfqq);
}

/*
 * Budget timeout is not implemented through a dedicated timer, but
 * just checked on request arrivals and completions, as well as on
 * idle timer expirations.
 */
static bool bfq_bfqq_budget_timeout(struct bfq_queue *bfqq)
{
        if (bfq_bfqq_budget_new(bfqq) ||
            time_is_after_jiffies(bfqq->budget_timeout))
                return false;
        return true;
}

/*
 * If we expire a queue that is actively waiting (i.e., with the
 * device idled) for the arrival of a new request, then we may incur
 * the timestamp misalignment problem described in the body of the
 * function __bfq_activate_entity. Hence we return true only if this
 * condition does not hold, or if the queue is slow enough to deserve
 * only to be kicked off for preserving a high throughput.
 */
static bool bfq_may_expire_for_budg_timeout(struct bfq_queue *bfqq)
{
        bfq_log_bfqq(bfqq->bfqd, bfqq,
                "may_budget_timeout: wait_request %d left %d timeout %d",
                bfq_bfqq_wait_request(bfqq),
                        bfq_bfqq_budget_left(bfqq) >=  bfqq->entity.budget / 3,
                bfq_bfqq_budget_timeout(bfqq));

        return (!bfq_bfqq_wait_request(bfqq) ||
                bfq_bfqq_budget_left(bfqq) >=  bfqq->entity.budget / 3)
                &&
                bfq_bfqq_budget_timeout(bfqq);
}

/*
 * For a queue that becomes empty, device idling is allowed only if
 * this function returns true for the queue. And this function returns
 * true only if idling is beneficial for throughput.
 */
static bool bfq_bfqq_may_idle(struct bfq_queue *bfqq)
{
        struct bfq_data *bfqd = bfqq->bfqd;
        bool idling_boosts_thr;

        if (bfqd->strict_guarantees)
                return true;

        /*
         * The value of the next variable is computed considering that
         * idling is usually beneficial for the throughput if:
         * (a) the device is not NCQ-capable, or
         * (b) regardless of the presence of NCQ, the request pattern
         *     for bfqq is I/O-bound (possible throughput losses
         *     caused by granting idling to seeky queues are mitigated
         *     by the fact that, in all scenarios where boosting
         *     throughput is the best thing to do, i.e., in all
         *     symmetric scenarios, only a minimal idle time is
         *     allowed to seeky queues).
         */
        idling_boosts_thr = !bfqd->hw_tag || bfq_bfqq_IO_bound(bfqq);

        /*
         * We have now the components we need to compute the return
         * value of the function, which is true only if both the
         * following conditions hold:
         * 1) bfqq is sync, because idling make sense only for sync queues;
         * 2) idling boosts the throughput.
         */
        return bfq_bfqq_sync(bfqq) && idling_boosts_thr;
}

/*
 * If the in-service queue is empty but the function bfq_bfqq_may_idle
 * returns true, then:
 * 1) the queue must remain in service and cannot be expired, and
 * 2) the device must be idled to wait for the possible arrival of a new
 *    request for the queue.
 * See the comments on the function bfq_bfqq_may_idle for the reasons
 * why performing device idling is the best choice to boost the throughput
 * and preserve service guarantees when bfq_bfqq_may_idle itself
 * returns true.
 */
static bool bfq_bfqq_must_idle(struct bfq_queue *bfqq)
{
        struct bfq_data *bfqd = bfqq->bfqd;

        return RB_EMPTY_ROOT(&bfqq->sort_list) && bfqd->bfq_slice_idle != 0 &&
               bfq_bfqq_may_idle(bfqq);
}

/*
 * Select a queue for service.  If we have a current queue in service,
 * check whether to continue servicing it, or retrieve and set a new one.
 */
static struct bfq_queue *bfq_select_queue(struct bfq_data *bfqd)
{
        struct bfq_queue *bfqq;
        struct request *next_rq;
        enum bfqq_expiration reason = BFQQE_BUDGET_TIMEOUT;

        bfqq = bfqd->in_service_queue;
        if (!bfqq)
                goto new_queue;

        bfq_log_bfqq(bfqd, bfqq, "select_queue: already in-service queue");

        if (bfq_may_expire_for_budg_timeout(bfqq) &&
            !bfq_bfqq_wait_request(bfqq) &&
            !bfq_bfqq_must_idle(bfqq))
                goto expire;

check_queue:
        /*
         * This loop is rarely executed more than once. Even when it
         * happens, it is much more convenient to re-execute this loop
         * than to return NULL and trigger a new dispatch to get a
         * request served.
         */
        next_rq = bfqq->next_rq;
        /*
         * If bfqq has requests queued and it has enough budget left to
         * serve them, keep the queue, otherwise expire it.
         */
        if (next_rq) {
                if (bfq_serv_to_charge(next_rq, bfqq) >
                        bfq_bfqq_budget_left(bfqq)) {
                        /*
                         * Expire the queue for budget exhaustion,
                         * which makes sure that the next budget is
                         * enough to serve the next request, even if
                         * it comes from the fifo expired path.
                         */
                        reason = BFQQE_BUDGET_EXHAUSTED;
                        goto expire;
                } else {
                        /*
                         * The idle timer may be pending because we may
                         * not disable disk idling even when a new request
                         * arrives.
                         */
                        if (bfq_bfqq_wait_request(bfqq)) {
                                /*
                                 * If we get here: 1) at least a new request
                                 * has arrived but we have not disabled the
                                 * timer because the request was too small,
                                 * 2) then the block layer has unplugged
                                 * the device, causing the dispatch to be
                                 * invoked.
                                 *
                                 * Since the device is unplugged, now the
                                 * requests are probably large enough to
                                 * provide a reasonable throughput.
                                 * So we disable idling.
                                 */
                                bfq_clear_bfqq_wait_request(bfqq);
                                hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
                                bfqg_stats_update_idle_time(bfqq_group(bfqq));
                        }
                        goto keep_queue;
                }
        }

        /*
         * No requests pending. However, if the in-service queue is idling
         * for a new request, or has requests waiting for a completion and
         * may idle after their completion, then keep it anyway.
         */
        if (bfq_bfqq_wait_request(bfqq) ||
            (bfqq->dispatched != 0 && bfq_bfqq_may_idle(bfqq))) {
                bfqq = NULL;
                goto keep_queue;
        }

        reason = BFQQE_NO_MORE_REQUESTS;
expire:
        bfq_bfqq_expire(bfqd, bfqq, false, reason);
new_queue:
        bfqq = bfq_set_in_service_queue(bfqd);
        if (bfqq) {
                bfq_log_bfqq(bfqd, bfqq, "select_queue: checking new queue");
                goto check_queue;
        }
keep_queue:
        if (bfqq)
                bfq_log_bfqq(bfqd, bfqq, "select_queue: returned this queue");
        else
                bfq_log(bfqd, "select_queue: no queue returned");

        return bfqq;
}

/*
 * Dispatch next request from bfqq.
 */
static struct request *bfq_dispatch_rq_from_bfqq(struct bfq_data *bfqd,
                                                 struct bfq_queue *bfqq)
{
        struct request *rq = bfqq->next_rq;
        unsigned long service_to_charge;

        service_to_charge = bfq_serv_to_charge(rq, bfqq);

        bfq_bfqq_served(bfqq, service_to_charge);

        bfq_dispatch_remove(bfqd->queue, rq);

        if (!bfqd->in_service_bic) {
                atomic_long_inc(&RQ_BIC(rq)->icq.ioc->refcount);
                bfqd->in_service_bic = RQ_BIC(rq);
        }

        /*
         * Expire bfqq, pretending that its budget expired, if bfqq
         * belongs to CLASS_IDLE and other queues are waiting for
         * service.
         */
        if (bfqd->busy_queues > 1 && bfq_class_idle(bfqq))
                goto expire;

        return rq;

expire:
        bfq_bfqq_expire(bfqd, bfqq, false, BFQQE_BUDGET_EXHAUSTED);
        return rq;
}

static bool bfq_has_work(struct blk_mq_hw_ctx *hctx)
{
        struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;

        /*
         * Avoiding lock: a race on bfqd->busy_queues should cause at
         * most a call to dispatch for nothing
         */
        return !list_empty_careful(&bfqd->dispatch) ||
                bfqd->busy_queues > 0;
}

static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
{
        struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
        struct request *rq = NULL;
        struct bfq_queue *bfqq = NULL;

        if (!list_empty(&bfqd->dispatch)) {
                rq = list_first_entry(&bfqd->dispatch, struct request,
                                      queuelist);
                list_del_init(&rq->queuelist);

                bfqq = RQ_BFQQ(rq);

                if (bfqq) {
                        /*
                         * Increment counters here, because this
                         * dispatch does not follow the standard
                         * dispatch flow (where counters are
                         * incremented)
                         */
                        bfqq->dispatched++;

                        goto inc_in_driver_start_rq;
                }

                /*
                 * We exploit the put_rq_private hook to decrement
                 * rq_in_driver, but put_rq_private will not be
                 * invoked on this request. So, to avoid unbalance,
                 * just start this request, without incrementing
                 * rq_in_driver. As a negative consequence,
                 * rq_in_driver is deceptively lower than it should be
                 * while this request is in service. This may cause
                 * bfq_schedule_dispatch to be invoked uselessly.
                 *
                 * As for implementing an exact solution, the
                 * put_request hook, if defined, is probably invoked
                 * also on this request. So, by exploiting this hook,
                 * we could 1) increment rq_in_driver here, and 2)
                 * decrement it in put_request. Such a solution would
                 * let the value of the counter be always accurate,
                 * but it would entail using an extra interface
                 * function. This cost seems higher than the benefit,
                 * being the frequency of non-elevator-private
                 * requests very low.
                 */
                goto start_rq;
        }

        bfq_log(bfqd, "dispatch requests: %d busy queues", bfqd->busy_queues);

        if (bfqd->busy_queues == 0)
                goto exit;

        /*
         * Force device to serve one request at a time if
         * strict_guarantees is true. Forcing this service scheme is
         * currently the ONLY way to guarantee that the request
         * service order enforced by the scheduler is respected by a
         * queueing device. Otherwise the device is free even to make
         * some unlucky request wait for as long as the device
         * wishes.
         *
         * Of course, serving one request at at time may cause loss of
         * throughput.
         */
        if (bfqd->strict_guarantees && bfqd->rq_in_driver > 0)
                goto exit;

        bfqq = bfq_select_queue(bfqd);
        if (!bfqq)
                goto exit;

        rq = bfq_dispatch_rq_from_bfqq(bfqd, bfqq);

        if (rq) {
inc_in_driver_start_rq:
                bfqd->rq_in_driver++;
start_rq:
                rq->rq_flags |= RQF_STARTED;
        }
exit:
        return rq;
}

static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
{
        struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
        struct request *rq;

        spin_lock_irq(&bfqd->lock);
        rq = __bfq_dispatch_request(hctx);
        spin_unlock_irq(&bfqd->lock);

        return rq;
}

/*
 * Task holds one reference to the queue, dropped when task exits.  Each rq
 * in-flight on this queue also holds a reference, dropped when rq is freed.
 *
 * Scheduler lock must be held here. Recall not to use bfqq after calling
 * this function on it.
 */
static void bfq_put_queue(struct bfq_queue *bfqq)
{
#ifdef CONFIG_BFQ_GROUP_IOSCHED
        struct bfq_group *bfqg = bfqq_group(bfqq);
#endif

        if (bfqq->bfqd)
                bfq_log_bfqq(bfqq->bfqd, bfqq, "put_queue: %p %d",
                             bfqq, bfqq->ref);

        bfqq->ref--;
        if (bfqq->ref)
                return;

        bfq_log_bfqq(bfqq->bfqd, bfqq, "put_queue: %p freed", bfqq);

        kmem_cache_free(bfq_pool, bfqq);
#ifdef CONFIG_BFQ_GROUP_IOSCHED
        bfqg_put(bfqg);
#endif
}

static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
{
        if (bfqq == bfqd->in_service_queue) {
                __bfq_bfqq_expire(bfqd, bfqq);
                bfq_schedule_dispatch(bfqd);
        }

        bfq_log_bfqq(bfqd, bfqq, "exit_bfqq: %p, %d", bfqq, bfqq->ref);

        bfq_put_queue(bfqq); /* release process reference */
}

static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic, bool is_sync)
{
        struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
        struct bfq_data *bfqd;

        if (bfqq)
                bfqd = bfqq->bfqd; /* NULL if scheduler already exited */

        if (bfqq && bfqd) {
                unsigned long flags;

                spin_lock_irqsave(&bfqd->lock, flags);
                bfq_exit_bfqq(bfqd, bfqq);
                bic_set_bfqq(bic, NULL, is_sync);
                spin_unlock_irq(&bfqd->lock);
        }
}

static void bfq_exit_icq(struct io_cq *icq)
{
        struct bfq_io_cq *bic = icq_to_bic(icq);

        bfq_exit_icq_bfqq(bic, true);
        bfq_exit_icq_bfqq(bic, false);
}

/*
 * Update the entity prio values; note that the new values will not
 * be used until the next (re)activation.
 */
static void
bfq_set_next_ioprio_data(struct bfq_queue *bfqq, struct bfq_io_cq *bic)
{
        struct task_struct *tsk = current;
        int ioprio_class;
        struct bfq_data *bfqd = bfqq->bfqd;

        if (!bfqd)
                return;

        ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
        switch (ioprio_class) {
        default:
                dev_err(bfqq->bfqd->queue->backing_dev_info->dev,
                        "bfq: bad prio class %d\n", ioprio_class);
        case IOPRIO_CLASS_NONE:
                /*
                 * No prio set, inherit CPU scheduling settings.
                 */
                bfqq->new_ioprio = task_nice_ioprio(tsk);
                bfqq->new_ioprio_class = task_nice_ioclass(tsk);
                break;
        case IOPRIO_CLASS_RT:
                bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
                bfqq->new_ioprio_class = IOPRIO_CLASS_RT;
                break;
        case IOPRIO_CLASS_BE:
                bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
                bfqq->new_ioprio_class = IOPRIO_CLASS_BE;
                break;
        case IOPRIO_CLASS_IDLE:
                bfqq->new_ioprio_class = IOPRIO_CLASS_IDLE;
                bfqq->new_ioprio = 7;
                bfq_clear_bfqq_idle_window(bfqq);
                break;
        }

        if (bfqq->new_ioprio >= IOPRIO_BE_NR) {
                pr_crit("bfq_set_next_ioprio_data: new_ioprio %d\n",
                        bfqq->new_ioprio);
                bfqq->new_ioprio = IOPRIO_BE_NR;
        }

        bfqq->entity.new_weight = bfq_ioprio_to_weight(bfqq->new_ioprio);
        bfqq->entity.prio_changed = 1;
}

static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio)
{
        struct bfq_data *bfqd = bic_to_bfqd(bic);
        struct bfq_queue *bfqq;
        int ioprio = bic->icq.ioc->ioprio;

        /*
         * This condition may trigger on a newly created bic, be sure to
         * drop the lock before returning.
         */
        if (unlikely(!bfqd) || likely(bic->ioprio == ioprio))
                return;

        bic->ioprio = ioprio;

        bfqq = bic_to_bfqq(bic, false);
        if (bfqq) {
                /* release process reference on this queue */
                bfq_put_queue(bfqq);
                bfqq = bfq_get_queue(bfqd, bio, BLK_RW_ASYNC, bic);
                bic_set_bfqq(bic, bfqq, false);
        }

        bfqq = bic_to_bfqq(bic, true);
        if (bfqq)
                bfq_set_next_ioprio_data(bfqq, bic);
}

static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
                          struct bfq_io_cq *bic, pid_t pid, int is_sync)
{
        RB_CLEAR_NODE(&bfqq->entity.rb_node);
        INIT_LIST_HEAD(&bfqq->fifo);

        bfqq->ref = 0;
        bfqq->bfqd = bfqd;

        if (bic)
                bfq_set_next_ioprio_data(bfqq, bic);

        if (is_sync) {
                if (!bfq_class_idle(bfqq))
                        bfq_mark_bfqq_idle_window(bfqq);
                bfq_mark_bfqq_sync(bfqq);
        } else
                bfq_clear_bfqq_sync(bfqq);

        /* set end request to minus infinity from now */
        bfqq->ttime.last_end_request = ktime_get_ns() + 1;

        bfq_mark_bfqq_IO_bound(bfqq);

        bfqq->pid = pid;

        /* Tentative initial value to trade off between thr and lat */
        bfqq->max_budget = (2 * bfq_max_budget(bfqd)) / 3;
        bfqq->budget_timeout = bfq_smallest_from_now();

        /* first request is almost certainly seeky */
        bfqq->seek_history = 1;
}

static struct bfq_queue **bfq_async_queue_prio(struct bfq_data *bfqd,
                                               struct bfq_group *bfqg,
                                               int ioprio_class, int ioprio)
{
        switch (ioprio_class) {
        case IOPRIO_CLASS_RT:
                return &bfqg->async_bfqq[0][ioprio];
        case IOPRIO_CLASS_NONE:
                ioprio = IOPRIO_NORM;
                /* fall through */
        case IOPRIO_CLASS_BE:
                return &bfqg->async_bfqq[1][ioprio];
        case IOPRIO_CLASS_IDLE:
                return &bfqg->async_idle_bfqq;
        default:
                return NULL;
        }
}

static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
                                       struct bio *bio, bool is_sync,
                                       struct bfq_io_cq *bic)
{
        const int ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
        const int ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
        struct bfq_queue **async_bfqq = NULL;
        struct bfq_queue *bfqq;
        struct bfq_group *bfqg;

        rcu_read_lock();

        bfqg = bfq_find_set_group(bfqd, bio_blkcg(bio));
        if (!bfqg) {
                bfqq = &bfqd->oom_bfqq;
                goto out;
        }

        if (!is_sync) {
                async_bfqq = bfq_async_queue_prio(bfqd, bfqg, ioprio_class,
                                                  ioprio);
                bfqq = *async_bfqq;
                if (bfqq)
                        goto out;
        }

        bfqq = kmem_cache_alloc_node(bfq_pool,
                                     GFP_NOWAIT | __GFP_ZERO | __GFP_NOWARN,
                                     bfqd->queue->node);

        if (bfqq) {
                bfq_init_bfqq(bfqd, bfqq, bic, current->pid,
                              is_sync);
                bfq_init_entity(&bfqq->entity, bfqg);
                bfq_log_bfqq(bfqd, bfqq, "allocated");
        } else {
                bfqq = &bfqd->oom_bfqq;
                bfq_log_bfqq(bfqd, bfqq, "using oom bfqq");
                goto out;
        }

        /*
         * Pin the queue now that it's allocated, scheduler exit will
         * prune it.
         */
        if (async_bfqq) {
                bfqq->ref++; /*
                              * Extra group reference, w.r.t. sync
                              * queue. This extra reference is removed
                              * only if bfqq->bfqg disappears, to
                              * guarantee that this queue is not freed
                              * until its group goes away.
                              */
                bfq_log_bfqq(bfqd, bfqq, "get_queue, bfqq not in async: %p, %d",
                             bfqq, bfqq->ref);
                *async_bfqq = bfqq;
        }

out:
        bfqq->ref++; /* get a process reference to this queue */
        bfq_log_bfqq(bfqd, bfqq, "get_queue, at end: %p, %d", bfqq, bfqq->ref);
        rcu_read_unlock();
        return bfqq;
}

static void bfq_update_io_thinktime(struct bfq_data *bfqd,
                                    struct bfq_queue *bfqq)
{
        struct bfq_ttime *ttime = &bfqq->ttime;
        u64 elapsed = ktime_get_ns() - bfqq->ttime.last_end_request;

        elapsed = min_t(u64, elapsed, 2ULL * bfqd->bfq_slice_idle);

        ttime->ttime_samples = (7*bfqq->ttime.ttime_samples + 256) / 8;
        ttime->ttime_total = div_u64(7*ttime->ttime_total + 256*elapsed,  8);
        ttime->ttime_mean = div64_ul(ttime->ttime_total + 128,
                                     ttime->ttime_samples);
}

static void
bfq_update_io_seektime(struct bfq_data *bfqd, struct bfq_queue *bfqq,
                       struct request *rq)
{
        bfqq->seek_history <<= 1;
        bfqq->seek_history |=
                get_sdist(bfqq->last_request_pos, rq) > BFQQ_SEEK_THR &&
                (!blk_queue_nonrot(bfqd->queue) ||
                 blk_rq_sectors(rq) < BFQQ_SECT_THR_NONROT);
}

/*
 * Disable idle window if the process thinks too long or seeks so much that
 * it doesn't matter.
 */
static void bfq_update_idle_window(struct bfq_data *bfqd,
                                   struct bfq_queue *bfqq,
                                   struct bfq_io_cq *bic)
{
        int enable_idle;

        /* Don't idle for async or idle io prio class. */
        if (!bfq_bfqq_sync(bfqq) || bfq_class_idle(bfqq))
                return;

        enable_idle = bfq_bfqq_idle_window(bfqq);

        if (atomic_read(&bic->icq.ioc->active_ref) == 0 ||
            bfqd->bfq_slice_idle == 0 ||
                (bfqd->hw_tag && BFQQ_SEEKY(bfqq)))
                enable_idle = 0;
        else if (bfq_sample_valid(bfqq->ttime.ttime_samples)) {
                if (bfqq->ttime.ttime_mean > bfqd->bfq_slice_idle)
                        enable_idle = 0;
                else
                        enable_idle = 1;
        }
        bfq_log_bfqq(bfqd, bfqq, "update_idle_window: enable_idle %d",
                enable_idle);

        if (enable_idle)
                bfq_mark_bfqq_idle_window(bfqq);
        else
                bfq_clear_bfqq_idle_window(bfqq);
}

/*
 * Called when a new fs request (rq) is added to bfqq.  Check if there's
 * something we should do about it.
 */
static void bfq_rq_enqueued(struct bfq_data *bfqd, struct bfq_queue *bfqq,
                            struct request *rq)
{
        struct bfq_io_cq *bic = RQ_BIC(rq);

        if (rq->cmd_flags & REQ_META)
                bfqq->meta_pending++;

        bfq_update_io_thinktime(bfqd, bfqq);
        bfq_update_io_seektime(bfqd, bfqq, rq);
        if (bfqq->entity.service > bfq_max_budget(bfqd) / 8 ||
            !BFQQ_SEEKY(bfqq))
                bfq_update_idle_window(bfqd, bfqq, bic);

        bfq_log_bfqq(bfqd, bfqq,
                     "rq_enqueued: idle_window=%d (seeky %d)",
                     bfq_bfqq_idle_window(bfqq), BFQQ_SEEKY(bfqq));

        bfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq);

        if (bfqq == bfqd->in_service_queue && bfq_bfqq_wait_request(bfqq)) {
                bool small_req = bfqq->queued[rq_is_sync(rq)] == 1 &&
                                 blk_rq_sectors(rq) < 32;
                bool budget_timeout = bfq_bfqq_budget_timeout(bfqq);

                /*
                 * There is just this request queued: if the request
                 * is small and the queue is not to be expired, then
                 * just exit.
                 *
                 * In this way, if the device is being idled to wait
                 * for a new request from the in-service queue, we
                 * avoid unplugging the device and committing the
                 * device to serve just a small request. On the
                 * contrary, we wait for the block layer to decide
                 * when to unplug the device: hopefully, new requests
                 * will be merged to this one quickly, then the device
                 * will be unplugged and larger requests will be
                 * dispatched.
                 */
                if (small_req && !budget_timeout)
                        return;

                /*
                 * A large enough request arrived, or the queue is to
                 * be expired: in both cases disk idling is to be
                 * stopped, so clear wait_request flag and reset
                 * timer.
                 */
                bfq_clear_bfqq_wait_request(bfqq);
                hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
                bfqg_stats_update_idle_time(bfqq_group(bfqq));

                /*
                 * The queue is not empty, because a new request just
                 * arrived. Hence we can safely expire the queue, in
                 * case of budget timeout, without risking that the
                 * timestamps of the queue are not updated correctly.
                 * See [1] for more details.
                 */
                if (budget_timeout)
                        bfq_bfqq_expire(bfqd, bfqq, false,
                                        BFQQE_BUDGET_TIMEOUT);
        }
}

static void __bfq_insert_request(struct bfq_data *bfqd, struct request *rq)
{
        struct bfq_queue *bfqq = RQ_BFQQ(rq);

        bfq_add_request(rq);

        rq->fifo_time = ktime_get_ns() + bfqd->bfq_fifo_expire[rq_is_sync(rq)];
        list_add_tail(&rq->queuelist, &bfqq->fifo);

        bfq_rq_enqueued(bfqd, bfqq, rq);
}

static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
                               bool at_head)
{
        struct request_queue *q = hctx->queue;
        struct bfq_data *bfqd = q->elevator->elevator_data;

        spin_lock_irq(&bfqd->lock);
        if (blk_mq_sched_try_insert_merge(q, rq)) {
                spin_unlock_irq(&bfqd->lock);
                return;
        }

        spin_unlock_irq(&bfqd->lock);

        blk_mq_sched_request_inserted(rq);

        spin_lock_irq(&bfqd->lock);
        if (at_head || blk_rq_is_passthrough(rq)) {
                if (at_head)
                        list_add(&rq->queuelist, &bfqd->dispatch);
                else
                        list_add_tail(&rq->queuelist, &bfqd->dispatch);
        } else {
                __bfq_insert_request(bfqd, rq);

                if (rq_mergeable(rq)) {
                        elv_rqhash_add(q, rq);
                        if (!q->last_merge)
                                q->last_merge = rq;
                }
        }

        spin_unlock_irq(&bfqd->lock);
}

static void bfq_insert_requests(struct blk_mq_hw_ctx *hctx,
                                struct list_head *list, bool at_head)
{
        while (!list_empty(list)) {
                struct request *rq;

                rq = list_first_entry(list, struct request, queuelist);
                list_del_init(&rq->queuelist);
                bfq_insert_request(hctx, rq, at_head);
        }
}

static void bfq_update_hw_tag(struct bfq_data *bfqd)
{
        bfqd->max_rq_in_driver = max_t(int, bfqd->max_rq_in_driver,
                                       bfqd->rq_in_driver);

        if (bfqd->hw_tag == 1)
                return;

        /*
         * This sample is valid if the number of outstanding requests
         * is large enough to allow a queueing behavior.  Note that the
         * sum is not exact, as it's not taking into account deactivated
         * requests.
         */
        if (bfqd->rq_in_driver + bfqd->queued < BFQ_HW_QUEUE_THRESHOLD)
                return;

        if (bfqd->hw_tag_samples++ < BFQ_HW_QUEUE_SAMPLES)
                return;

        bfqd->hw_tag = bfqd->max_rq_in_driver > BFQ_HW_QUEUE_THRESHOLD;
        bfqd->max_rq_in_driver = 0;
        bfqd->hw_tag_samples = 0;
}

static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd)
{
        u64 now_ns;
        u32 delta_us;

        bfq_update_hw_tag(bfqd);

        bfqd->rq_in_driver--;
        bfqq->dispatched--;

        now_ns = ktime_get_ns();

        bfqq->ttime.last_end_request = now_ns;

        /*
         * Using us instead of ns, to get a reasonable precision in
         * computing rate in next check.
         */
        delta_us = div_u64(now_ns - bfqd->last_completion, NSEC_PER_USEC);

        /*
         * If the request took rather long to complete, and, according
         * to the maximum request size recorded, this completion latency
         * implies that the request was certainly served at a very low
         * rate (less than 1M sectors/sec), then the whole observation
         * interval that lasts up to this time instant cannot be a
         * valid time interval for computing a new peak rate.  Invoke
         * bfq_update_rate_reset to have the following three steps
         * taken:
         * - close the observation interval at the last (previous)
         *   request dispatch or completion
         * - compute rate, if possible, for that observation interval
         * - reset to zero samples, which will trigger a proper
         *   re-initialization of the observation interval on next
         *   dispatch
         */
        if (delta_us > BFQ_MIN_TT/NSEC_PER_USEC &&
           (bfqd->last_rq_max_size<<BFQ_RATE_SHIFT)/delta_us <
                        1UL<<(BFQ_RATE_SHIFT - 10))
                bfq_update_rate_reset(bfqd, NULL);
        bfqd->last_completion = now_ns;

        /*
         * If this is the in-service queue, check if it needs to be expired,
         * or if we want to idle in case it has no pending requests.
         */
        if (bfqd->in_service_queue == bfqq) {
                if (bfq_bfqq_budget_new(bfqq))
                        bfq_set_budget_timeout(bfqd);

                if (bfq_bfqq_must_idle(bfqq)) {
                        bfq_arm_slice_timer(bfqd);
                        return;
                } else if (bfq_may_expire_for_budg_timeout(bfqq))
                        bfq_bfqq_expire(bfqd, bfqq, false,
                                        BFQQE_BUDGET_TIMEOUT);
                else if (RB_EMPTY_ROOT(&bfqq->sort_list) &&
                         (bfqq->dispatched == 0 ||
                          !bfq_bfqq_may_idle(bfqq)))
                        bfq_bfqq_expire(bfqd, bfqq, false,
                                        BFQQE_NO_MORE_REQUESTS);
        }
}

static void bfq_put_rq_priv_body(struct bfq_queue *bfqq)
{
        bfqq->allocated--;

        bfq_put_queue(bfqq);
}

static void bfq_put_rq_private(struct request_queue *q, struct request *rq)
{
        struct bfq_queue *bfqq = RQ_BFQQ(rq);
        struct bfq_data *bfqd = bfqq->bfqd;

        if (rq->rq_flags & RQF_STARTED)
                bfqg_stats_update_completion(bfqq_group(bfqq),
                                             rq_start_time_ns(rq),
                                             rq_io_start_time_ns(rq),
                                             rq->cmd_flags);

        if (likely(rq->rq_flags & RQF_STARTED)) {
                unsigned long flags;

                spin_lock_irqsave(&bfqd->lock, flags);

                bfq_completed_request(bfqq, bfqd);
                bfq_put_rq_priv_body(bfqq);

                spin_unlock_irqrestore(&bfqd->lock, flags);
        } else {
                /*
                 * Request rq may be still/already in the scheduler,
                 * in which case we need to remove it. And we cannot
                 * defer such a check and removal, to avoid
                 * inconsistencies in the time interval from the end
                 * of this function to the start of the deferred work.
                 * This situation seems to occur only in process
                 * context, as a consequence of a merge. In the
                 * current version of the code, this implies that the
                 * lock is held.
                 */

                if (!RB_EMPTY_NODE(&rq->rb_node))
                        bfq_remove_request(q, rq);
                bfq_put_rq_priv_body(bfqq);
        }

        rq->elv.priv[0] = NULL;
        rq->elv.priv[1] = NULL;
}

/*
 * Allocate bfq data structures associated with this request.
 */
static int bfq_get_rq_private(struct request_queue *q, struct request *rq,
                              struct bio *bio)
{
        struct bfq_data *bfqd = q->elevator->elevator_data;
        struct bfq_io_cq *bic = icq_to_bic(rq->elv.icq);
        const int is_sync = rq_is_sync(rq);
        struct bfq_queue *bfqq;

        spin_lock_irq(&bfqd->lock);

        bfq_check_ioprio_change(bic, bio);

        if (!bic)
                goto queue_fail;

        bfq_bic_update_cgroup(bic, bio);

        bfqq = bic_to_bfqq(bic, is_sync);
        if (!bfqq || bfqq == &bfqd->oom_bfqq) {
                if (bfqq)
                        bfq_put_queue(bfqq);
                bfqq = bfq_get_queue(bfqd, bio, is_sync, bic);
                bic_set_bfqq(bic, bfqq, is_sync);
        }

        bfqq->allocated++;
        bfqq->ref++;
        bfq_log_bfqq(bfqd, bfqq, "get_request %p: bfqq %p, %d",
                     rq, bfqq, bfqq->ref);

        rq->elv.priv[0] = bic;
        rq->elv.priv[1] = bfqq;

        spin_unlock_irq(&bfqd->lock);

        return 0;

queue_fail:
        spin_unlock_irq(&bfqd->lock);

        return 1;
}

static void bfq_idle_slice_timer_body(struct bfq_queue *bfqq)
{
        struct bfq_data *bfqd = bfqq->bfqd;
        enum bfqq_expiration reason;
        unsigned long flags;

        spin_lock_irqsave(&bfqd->lock, flags);
        bfq_clear_bfqq_wait_request(bfqq);

        if (bfqq != bfqd->in_service_queue) {
                spin_unlock_irqrestore(&bfqd->lock, flags);
                return;
        }

        if (bfq_bfqq_budget_timeout(bfqq))
                /*
                 * Also here the queue can be safely expired
                 * for budget timeout without wasting
                 * guarantees
                 */
                reason = BFQQE_BUDGET_TIMEOUT;
        else if (bfqq->queued[0] == 0 && bfqq->queued[1] == 0)
                /*
                 * The queue may not be empty upon timer expiration,
                 * because we may not disable the timer when the
                 * first request of the in-service queue arrives
                 * during disk idling.
                 */
                reason = BFQQE_TOO_IDLE;
        else
                goto schedule_dispatch;

        bfq_bfqq_expire(bfqd, bfqq, true, reason);

schedule_dispatch:
        spin_unlock_irqrestore(&bfqd->lock, flags);
        bfq_schedule_dispatch(bfqd);
}

/*
 * Handler of the expiration of the timer running if the in-service queue
 * is idling inside its time slice.
 */
static enum hrtimer_restart bfq_idle_slice_timer(struct hrtimer *timer)
{
        struct bfq_data *bfqd = container_of(timer, struct bfq_data,
                                             idle_slice_timer);
        struct bfq_queue *bfqq = bfqd->in_service_queue;

        /*
         * Theoretical race here: the in-service queue can be NULL or
         * different from the queue that was idling if a new request
         * arrives for the current queue and there is a full dispatch
         * cycle that changes the in-service queue.  This can hardly
         * happen, but in the worst case we just expire a queue too
         * early.
         */
        if (bfqq)
                bfq_idle_slice_timer_body(bfqq);

        return HRTIMER_NORESTART;
}

static void __bfq_put_async_bfqq(struct bfq_data *bfqd,
                                 struct bfq_queue **bfqq_ptr)
{
        struct bfq_queue *bfqq = *bfqq_ptr;

        bfq_log(bfqd, "put_async_bfqq: %p", bfqq);
        if (bfqq) {
                bfq_bfqq_move(bfqd, bfqq, bfqd->root_group);

                bfq_log_bfqq(bfqd, bfqq, "put_async_bfqq: putting %p, %d",
                             bfqq, bfqq->ref);
                bfq_put_queue(bfqq);
                *bfqq_ptr = NULL;
        }
}

/*
 * Release all the bfqg references to its async queues.  If we are
 * deallocating the group these queues may still contain requests, so
 * we reparent them to the root cgroup (i.e., the only one that will
 * exist for sure until all the requests on a device are gone).
 */
static void bfq_put_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg)
{
        int i, j;

        for (i = 0; i < 2; i++)
                for (j = 0; j < IOPRIO_BE_NR; j++)
                        __bfq_put_async_bfqq(bfqd, &bfqg->async_bfqq[i][j]);

        __bfq_put_async_bfqq(bfqd, &bfqg->async_idle_bfqq);
}

static void bfq_exit_queue(struct elevator_queue *e)
{
        struct bfq_data *bfqd = e->elevator_data;
        struct bfq_queue *bfqq, *n;

        hrtimer_cancel(&bfqd->idle_slice_timer);

        spin_lock_irq(&bfqd->lock);
        list_for_each_entry_safe(bfqq, n, &bfqd->idle_list, bfqq_list)
                bfq_deactivate_bfqq(bfqd, bfqq, false, false);
        spin_unlock_irq(&bfqd->lock);

        hrtimer_cancel(&bfqd->idle_slice_timer);

#ifdef CONFIG_BFQ_GROUP_IOSCHED
        blkcg_deactivate_policy(bfqd->queue, &blkcg_policy_bfq);
#else
        spin_lock_irq(&bfqd->lock);
        bfq_put_async_queues(bfqd, bfqd->root_group);
        kfree(bfqd->root_group);
        spin_unlock_irq(&bfqd->lock);
#endif

        kfree(bfqd);
}

static void bfq_init_root_group(struct bfq_group *root_group,
                                struct bfq_data *bfqd)
{
        int i;

#ifdef CONFIG_BFQ_GROUP_IOSCHED
        root_group->entity.parent = NULL;
        root_group->my_entity = NULL;
        root_group->bfqd = bfqd;
#endif
        for (i = 0; i < BFQ_IOPRIO_CLASSES; i++)
                root_group->sched_data.service_tree[i] = BFQ_SERVICE_TREE_INIT;
        root_group->sched_data.bfq_class_idle_last_service = jiffies;
}

static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
{
        struct bfq_data *bfqd;
        struct elevator_queue *eq;

        eq = elevator_alloc(q, e);
        if (!eq)
                return -ENOMEM;

        bfqd = kzalloc_node(sizeof(*bfqd), GFP_KERNEL, q->node);
        if (!bfqd) {
                kobject_put(&eq->kobj);
                return -ENOMEM;
        }
        eq->elevator_data = bfqd;

        spin_lock_irq(q->queue_lock);
        q->elevator = eq;
        spin_unlock_irq(q->queue_lock);

        /*
         * Our fallback bfqq if bfq_find_alloc_queue() runs into OOM issues.
         * Grab a permanent reference to it, so that the normal code flow
         * will not attempt to free it.
         */
        bfq_init_bfqq(bfqd, &bfqd->oom_bfqq, NULL, 1, 0);
        bfqd->oom_bfqq.ref++;
        bfqd->oom_bfqq.new_ioprio = BFQ_DEFAULT_QUEUE_IOPRIO;
        bfqd->oom_bfqq.new_ioprio_class = IOPRIO_CLASS_BE;
        bfqd->oom_bfqq.entity.new_weight =
                bfq_ioprio_to_weight(bfqd->oom_bfqq.new_ioprio);
        /*
         * Trigger weight initialization, according to ioprio, at the
         * oom_bfqq's first activation. The oom_bfqq's ioprio and ioprio
         * class won't be changed any more.
         */
        bfqd->oom_bfqq.entity.prio_changed = 1;

        bfqd->queue = q;

        INIT_LIST_HEAD(&bfqd->dispatch);

        hrtimer_init(&bfqd->idle_slice_timer, CLOCK_MONOTONIC,
                     HRTIMER_MODE_REL);
        bfqd->idle_slice_timer.function = bfq_idle_slice_timer;

        INIT_LIST_HEAD(&bfqd->active_list);
        INIT_LIST_HEAD(&bfqd->idle_list);

        bfqd->hw_tag = -1;

        bfqd->bfq_max_budget = bfq_default_max_budget;

        bfqd->bfq_fifo_expire[0] = bfq_fifo_expire[0];
        bfqd->bfq_fifo_expire[1] = bfq_fifo_expire[1];
        bfqd->bfq_back_max = bfq_back_max;
        bfqd->bfq_back_penalty = bfq_back_penalty;
        bfqd->bfq_slice_idle = bfq_slice_idle;
        bfqd->bfq_timeout = bfq_timeout;

        bfqd->bfq_requests_within_timer = 120;

        spin_lock_init(&bfqd->lock);

        /*
         * The invocation of the next bfq_create_group_hierarchy
         * function is the head of a chain of function calls
         * (bfq_create_group_hierarchy->blkcg_activate_policy->
         * blk_mq_freeze_queue) that may lead to the invocation of the
         * has_work hook function. For this reason,
         * bfq_create_group_hierarchy is invoked only after all
         * scheduler data has been initialized, apart from the fields
         * that can be initialized only after invoking
         * bfq_create_group_hierarchy. This, in particular, enables
         * has_work to correctly return false. Of course, to avoid
         * other inconsistencies, the blk-mq stack must then refrain
         * from invoking further scheduler hooks before this init
         * function is finished.
         */
        bfqd->root_group = bfq_create_group_hierarchy(bfqd, q->node);
        if (!bfqd->root_group)
                goto out_free;
        bfq_init_root_group(bfqd->root_group, bfqd);
        bfq_init_entity(&bfqd->oom_bfqq.entity, bfqd->root_group);


        return 0;

out_free:
        kfree(bfqd);
        kobject_put(&eq->kobj);
        return -ENOMEM;
}

static void bfq_slab_kill(void)
{
        kmem_cache_destroy(bfq_pool);
}

static int __init bfq_slab_setup(void)
{
        bfq_pool = KMEM_CACHE(bfq_queue, 0);
        if (!bfq_pool)
                return -ENOMEM;
        return 0;
}

static ssize_t bfq_var_show(unsigned int var, char *page)
{
        return sprintf(page, "%u\n", var);
}

static ssize_t bfq_var_store(unsigned long *var, const char *page,
                             size_t count)
{
        unsigned long new_val;
        int ret = kstrtoul(page, 10, &new_val);

        if (ret == 0)
                *var = new_val;

        return count;
}

#define SHOW_FUNCTION(__FUNC, __VAR, __CONV)                            \
static ssize_t __FUNC(struct elevator_queue *e, char *page)             \
{                                                                       \
        struct bfq_data *bfqd = e->elevator_data;                       \
        u64 __data = __VAR;                                             \
        if (__CONV == 1)                                                \
                __data = jiffies_to_msecs(__data);                      \
        else if (__CONV == 2)                                           \
                __data = div_u64(__data, NSEC_PER_MSEC);                \
        return bfq_var_show(__data, (page));                            \
}
SHOW_FUNCTION(bfq_fifo_expire_sync_show, bfqd->bfq_fifo_expire[1], 2);
SHOW_FUNCTION(bfq_fifo_expire_async_show, bfqd->bfq_fifo_expire[0], 2);
SHOW_FUNCTION(bfq_back_seek_max_show, bfqd->bfq_back_max, 0);
SHOW_FUNCTION(bfq_back_seek_penalty_show, bfqd->bfq_back_penalty, 0);
SHOW_FUNCTION(bfq_slice_idle_show, bfqd->bfq_slice_idle, 2);
SHOW_FUNCTION(bfq_max_budget_show, bfqd->bfq_user_max_budget, 0);
SHOW_FUNCTION(bfq_timeout_sync_show, bfqd->bfq_timeout, 1);
SHOW_FUNCTION(bfq_strict_guarantees_show, bfqd->strict_guarantees, 0);
#undef SHOW_FUNCTION

#define USEC_SHOW_FUNCTION(__FUNC, __VAR)                               \
static ssize_t __FUNC(struct elevator_queue *e, char *page)             \
{                                                                       \
        struct bfq_data *bfqd = e->elevator_data;                       \
        u64 __data = __VAR;                                             \
        __data = div_u64(__data, NSEC_PER_USEC);                        \
        return bfq_var_show(__data, (page));                            \
}
USEC_SHOW_FUNCTION(bfq_slice_idle_us_show, bfqd->bfq_slice_idle);
#undef USEC_SHOW_FUNCTION

#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)                 \
static ssize_t                                                          \
__FUNC(struct elevator_queue *e, const char *page, size_t count)        \
{                                                                       \
        struct bfq_data *bfqd = e->elevator_data;                       \
        unsigned long uninitialized_var(__data);                        \
        int ret = bfq_var_store(&__data, (page), count);                \
        if (__data < (MIN))                                             \
                __data = (MIN);                                         \
        else if (__data > (MAX))                                        \
                __data = (MAX);                                         \
        if (__CONV == 1)                                                \
                *(__PTR) = msecs_to_jiffies(__data);                    \
        else if (__CONV == 2)                                           \
                *(__PTR) = (u64)__data * NSEC_PER_MSEC;                 \
        else                                                            \
                *(__PTR) = __data;                                      \
        return ret;                                                     \
}
STORE_FUNCTION(bfq_fifo_expire_sync_store, &bfqd->bfq_fifo_expire[1], 1,
                INT_MAX, 2);
STORE_FUNCTION(bfq_fifo_expire_async_store, &bfqd->bfq_fifo_expire[0], 1,
                INT_MAX, 2);
STORE_FUNCTION(bfq_back_seek_max_store, &bfqd->bfq_back_max, 0, INT_MAX, 0);
STORE_FUNCTION(bfq_back_seek_penalty_store, &bfqd->bfq_back_penalty, 1,
                INT_MAX, 0);
STORE_FUNCTION(bfq_slice_idle_store, &bfqd->bfq_slice_idle, 0, INT_MAX, 2);
#undef STORE_FUNCTION

#define USEC_STORE_FUNCTION(__FUNC, __PTR, MIN, MAX)                    \
static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count)\
{                                                                       \
        struct bfq_data *bfqd = e->elevator_data;                       \
        unsigned long uninitialized_var(__data);                        \
        int ret = bfq_var_store(&__data, (page), count);                \
        if (__data < (MIN))                                             \
                __data = (MIN);                                         \
        else if (__data > (MAX))                                        \
                __data = (MAX);                                         \
        *(__PTR) = (u64)__data * NSEC_PER_USEC;                         \
        return ret;                                                     \
}
USEC_STORE_FUNCTION(bfq_slice_idle_us_store, &bfqd->bfq_slice_idle, 0,
                    UINT_MAX);
#undef USEC_STORE_FUNCTION

static ssize_t bfq_max_budget_store(struct elevator_queue *e,
                                    const char *page, size_t count)
{
        struct bfq_data *bfqd = e->elevator_data;
        unsigned long uninitialized_var(__data);
        int ret = bfq_var_store(&__data, (page), count);

        if (__data == 0)
                bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);
        else {
                if (__data > INT_MAX)
                        __data = INT_MAX;
                bfqd->bfq_max_budget = __data;
        }

        bfqd->bfq_user_max_budget = __data;

        return ret;
}

/*
 * Leaving this name to preserve name compatibility with cfq
 * parameters, but this timeout is used for both sync and async.
 */
static ssize_t bfq_timeout_sync_store(struct elevator_queue *e,
                                      const char *page, size_t count)
{
        struct bfq_data *bfqd = e->elevator_data;
        unsigned long uninitialized_var(__data);
        int ret = bfq_var_store(&__data, (page), count);

        if (__data < 1)
                __data = 1;
        else if (__data > INT_MAX)
                __data = INT_MAX;

        bfqd->bfq_timeout = msecs_to_jiffies(__data);
        if (bfqd->bfq_user_max_budget == 0)
                bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);

        return ret;
}

static ssize_t bfq_strict_guarantees_store(struct elevator_queue *e,
                                     const char *page, size_t count)
{
        struct bfq_data *bfqd = e->elevator_data;
        unsigned long uninitialized_var(__data);
        int ret = bfq_var_store(&__data, (page), count);

        if (__data > 1)
                __data = 1;
        if (!bfqd->strict_guarantees && __data == 1
            && bfqd->bfq_slice_idle < 8 * NSEC_PER_MSEC)
                bfqd->bfq_slice_idle = 8 * NSEC_PER_MSEC;

        bfqd->strict_guarantees = __data;

        return ret;
}

#define BFQ_ATTR(name) \
        __ATTR(name, 0644, bfq_##name##_show, bfq_##name##_store)

static struct elv_fs_entry bfq_attrs[] = {
        BFQ_ATTR(fifo_expire_sync),
        BFQ_ATTR(fifo_expire_async),
        BFQ_ATTR(back_seek_max),
        BFQ_ATTR(back_seek_penalty),
        BFQ_ATTR(slice_idle),
        BFQ_ATTR(slice_idle_us),
        BFQ_ATTR(max_budget),
        BFQ_ATTR(timeout_sync),
        BFQ_ATTR(strict_guarantees),
        __ATTR_NULL
};

static struct elevator_type iosched_bfq_mq = {
        .ops.mq = {
                .get_rq_priv            = bfq_get_rq_private,
                .put_rq_priv            = bfq_put_rq_private,
                .exit_icq               = bfq_exit_icq,
                .insert_requests        = bfq_insert_requests,
                .dispatch_request       = bfq_dispatch_request,
                .next_request           = elv_rb_latter_request,
                .former_request         = elv_rb_former_request,
                .allow_merge            = bfq_allow_bio_merge,
                .bio_merge              = bfq_bio_merge,
                .request_merge          = bfq_request_merge,
                .requests_merged        = bfq_requests_merged,
                .request_merged         = bfq_request_merged,
                .has_work               = bfq_has_work,
                .init_sched             = bfq_init_queue,
                .exit_sched             = bfq_exit_queue,
        },

        .uses_mq =              true,
        .icq_size =             sizeof(struct bfq_io_cq),
        .icq_align =            __alignof__(struct bfq_io_cq),
        .elevator_attrs =       bfq_attrs,
        .elevator_name =        "bfq",
        .elevator_owner =       THIS_MODULE,
};

#ifdef CONFIG_BFQ_GROUP_IOSCHED
static struct blkcg_policy blkcg_policy_bfq = {
        .dfl_cftypes            = bfq_blkg_files,
        .legacy_cftypes         = bfq_blkcg_legacy_files,

        .cpd_alloc_fn           = bfq_cpd_alloc,
        .cpd_init_fn            = bfq_cpd_init,
        .cpd_bind_fn            = bfq_cpd_init,
        .cpd_free_fn            = bfq_cpd_free,

        .pd_alloc_fn            = bfq_pd_alloc,
        .pd_init_fn             = bfq_pd_init,
        .pd_offline_fn          = bfq_pd_offline,
        .pd_free_fn             = bfq_pd_free,
        .pd_reset_stats_fn      = bfq_pd_reset_stats,
};
#endif

static int __init bfq_init(void)
{
        int ret;

#ifdef CONFIG_BFQ_GROUP_IOSCHED
        ret = blkcg_policy_register(&blkcg_policy_bfq);
        if (ret)
                return ret;
#endif

        ret = -ENOMEM;
        if (bfq_slab_setup())
                goto err_pol_unreg;

        ret = elv_register(&iosched_bfq_mq);
        if (ret)
                goto err_pol_unreg;

        return 0;

err_pol_unreg:
#ifdef CONFIG_BFQ_GROUP_IOSCHED
        blkcg_policy_unregister(&blkcg_policy_bfq);
#endif
        return ret;
}

static void __exit bfq_exit(void)
{
        elv_unregister(&iosched_bfq_mq);
#ifdef CONFIG_BFQ_GROUP_IOSCHED
        blkcg_policy_unregister(&blkcg_policy_bfq);
#endif
        bfq_slab_kill();
}

module_init(bfq_init);
module_exit(bfq_exit);

MODULE_AUTHOR("Paolo Valente");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("MQ Budget Fair Queueing I/O Scheduler");