blk-iocost: clamp inuse and skip noops in __propagate_weights()

[mirror_ubuntu-hirsute-kernel.git] / block / blk-iocost.c

/* SPDX-License-Identifier: GPL-2.0
 *
 * IO cost model based controller.
 *
 * Copyright (C) 2019 Tejun Heo <tj@kernel.org>
 * Copyright (C) 2019 Andy Newell <newella@fb.com>
 * Copyright (C) 2019 Facebook
 *
 * One challenge of controlling IO resources is the lack of trivially
 * observable cost metric.  This is distinguished from CPU and memory where
 * wallclock time and the number of bytes can serve as accurate enough
 * approximations.
 *
 * Bandwidth and iops are the most commonly used metrics for IO devices but
 * depending on the type and specifics of the device, different IO patterns
 * easily lead to multiple orders of magnitude variations rendering them
 * useless for the purpose of IO capacity distribution.  While on-device
 * time, with a lot of clutches, could serve as a useful approximation for
 * non-queued rotational devices, this is no longer viable with modern
 * devices, even the rotational ones.
 *
 * While there is no cost metric we can trivially observe, it isn't a
 * complete mystery.  For example, on a rotational device, seek cost
 * dominates while a contiguous transfer contributes a smaller amount
 * proportional to the size.  If we can characterize at least the relative
 * costs of these different types of IOs, it should be possible to
 * implement a reasonable work-conserving proportional IO resource
 * distribution.
 *
 * 1. IO Cost Model
 *
 * IO cost model estimates the cost of an IO given its basic parameters and
 * history (e.g. the end sector of the last IO).  The cost is measured in
 * device time.  If a given IO is estimated to cost 10ms, the device should
 * be able to process ~100 of those IOs in a second.
 *
 * Currently, there's only one builtin cost model - linear.  Each IO is
 * classified as sequential or random and given a base cost accordingly.
 * On top of that, a size cost proportional to the length of the IO is
 * added.  While simple, this model captures the operational
 * characteristics of a wide varienty of devices well enough.  Default
 * paramters for several different classes of devices are provided and the
 * parameters can be configured from userspace via
 * /sys/fs/cgroup/io.cost.model.
 *
 * If needed, tools/cgroup/iocost_coef_gen.py can be used to generate
 * device-specific coefficients.
 *
 * 2. Control Strategy
 *
 * The device virtual time (vtime) is used as the primary control metric.
 * The control strategy is composed of the following three parts.
 *
 * 2-1. Vtime Distribution
 *
 * When a cgroup becomes active in terms of IOs, its hierarchical share is
 * calculated.  Please consider the following hierarchy where the numbers
 * inside parentheses denote the configured weights.
 *
 *           root
 *         /       \
 *      A (w:100)  B (w:300)
 *      /       \
 *  A0 (w:100)  A1 (w:100)
 *
 * If B is idle and only A0 and A1 are actively issuing IOs, as the two are
 * of equal weight, each gets 50% share.  If then B starts issuing IOs, B
 * gets 300/(100+300) or 75% share, and A0 and A1 equally splits the rest,
 * 12.5% each.  The distribution mechanism only cares about these flattened
 * shares.  They're called hweights (hierarchical weights) and always add
 * upto 1 (HWEIGHT_WHOLE).
 *
 * A given cgroup's vtime runs slower in inverse proportion to its hweight.
 * For example, with 12.5% weight, A0's time runs 8 times slower (100/12.5)
 * against the device vtime - an IO which takes 10ms on the underlying
 * device is considered to take 80ms on A0.
 *
 * This constitutes the basis of IO capacity distribution.  Each cgroup's
 * vtime is running at a rate determined by its hweight.  A cgroup tracks
 * the vtime consumed by past IOs and can issue a new IO iff doing so
 * wouldn't outrun the current device vtime.  Otherwise, the IO is
 * suspended until the vtime has progressed enough to cover it.
 *
 * 2-2. Vrate Adjustment
 *
 * It's unrealistic to expect the cost model to be perfect.  There are too
 * many devices and even on the same device the overall performance
 * fluctuates depending on numerous factors such as IO mixture and device
 * internal garbage collection.  The controller needs to adapt dynamically.
 *
 * This is achieved by adjusting the overall IO rate according to how busy
 * the device is.  If the device becomes overloaded, we're sending down too
 * many IOs and should generally slow down.  If there are waiting issuers
 * but the device isn't saturated, we're issuing too few and should
 * generally speed up.
 *
 * To slow down, we lower the vrate - the rate at which the device vtime
 * passes compared to the wall clock.  For example, if the vtime is running
 * at the vrate of 75%, all cgroups added up would only be able to issue
 * 750ms worth of IOs per second, and vice-versa for speeding up.
 *
 * Device business is determined using two criteria - rq wait and
 * completion latencies.
 *
 * When a device gets saturated, the on-device and then the request queues
 * fill up and a bio which is ready to be issued has to wait for a request
 * to become available.  When this delay becomes noticeable, it's a clear
 * indication that the device is saturated and we lower the vrate.  This
 * saturation signal is fairly conservative as it only triggers when both
 * hardware and software queues are filled up, and is used as the default
 * busy signal.
 *
 * As devices can have deep queues and be unfair in how the queued commands
 * are executed, soley depending on rq wait may not result in satisfactory
 * control quality.  For a better control quality, completion latency QoS
 * parameters can be configured so that the device is considered saturated
 * if N'th percentile completion latency rises above the set point.
 *
 * The completion latency requirements are a function of both the
 * underlying device characteristics and the desired IO latency quality of
 * service.  There is an inherent trade-off - the tighter the latency QoS,
 * the higher the bandwidth lossage.  Latency QoS is disabled by default
 * and can be set through /sys/fs/cgroup/io.cost.qos.
 *
 * 2-3. Work Conservation
 *
 * Imagine two cgroups A and B with equal weights.  A is issuing a small IO
 * periodically while B is sending out enough parallel IOs to saturate the
 * device on its own.  Let's say A's usage amounts to 100ms worth of IO
 * cost per second, i.e., 10% of the device capacity.  The naive
 * distribution of half and half would lead to 60% utilization of the
 * device, a significant reduction in the total amount of work done
 * compared to free-for-all competition.  This is too high a cost to pay
 * for IO control.
 *
 * To conserve the total amount of work done, we keep track of how much
 * each active cgroup is actually using and yield part of its weight if
 * there are other cgroups which can make use of it.  In the above case,
 * A's weight will be lowered so that it hovers above the actual usage and
 * B would be able to use the rest.
 *
 * As we don't want to penalize a cgroup for donating its weight, the
 * surplus weight adjustment factors in a margin and has an immediate
 * snapback mechanism in case the cgroup needs more IO vtime for itself.
 *
 * Note that adjusting down surplus weights has the same effects as
 * accelerating vtime for other cgroups and work conservation can also be
 * implemented by adjusting vrate dynamically.  However, squaring who can
 * donate and should take back how much requires hweight propagations
 * anyway making it easier to implement and understand as a separate
 * mechanism.
 *
 * 3. Monitoring
 *
 * Instead of debugfs or other clumsy monitoring mechanisms, this
 * controller uses a drgn based monitoring script -
 * tools/cgroup/iocost_monitor.py.  For details on drgn, please see
 * https://github.com/osandov/drgn.  The ouput looks like the following.
 *
 *  sdb RUN   per=300ms cur_per=234.218:v203.695 busy= +1 vrate= 62.12%
 *                 active      weight      hweight% inflt% dbt  delay usages%
 *  test/a              *    50/   50  33.33/ 33.33  27.65   2  0*041 033:033:033
 *  test/b              *   100/  100  66.67/ 66.67  17.56   0  0*000 066:079:077
 *
 * - per        : Timer period
 * - cur_per    : Internal wall and device vtime clock
 * - vrate      : Device virtual time rate against wall clock
 * - weight     : Surplus-adjusted and configured weights
 * - hweight    : Surplus-adjusted and configured hierarchical weights
 * - inflt      : The percentage of in-flight IO cost at the end of last period
 * - del_ms     : Deferred issuer delay induction level and duration
 * - usages     : Usage history
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/timer.h>
#include <linux/time64.h>
#include <linux/parser.h>
#include <linux/sched/signal.h>
#include <linux/blk-cgroup.h>
#include <asm/local.h>
#include <asm/local64.h>
#include "blk-rq-qos.h"
#include "blk-stat.h"
#include "blk-wbt.h"

#ifdef CONFIG_TRACEPOINTS

/* copied from TRACE_CGROUP_PATH, see cgroup-internal.h */
#define TRACE_IOCG_PATH_LEN 1024
static DEFINE_SPINLOCK(trace_iocg_path_lock);
static char trace_iocg_path[TRACE_IOCG_PATH_LEN];

#define TRACE_IOCG_PATH(type, iocg, ...)                                        \
        do {                                                                    \
                unsigned long flags;                                            \
                if (trace_iocost_##type##_enabled()) {                          \
                        spin_lock_irqsave(&trace_iocg_path_lock, flags);        \
                        cgroup_path(iocg_to_blkg(iocg)->blkcg->css.cgroup,      \
                                    trace_iocg_path, TRACE_IOCG_PATH_LEN);      \
                        trace_iocost_##type(iocg, trace_iocg_path,              \
                                              ##__VA_ARGS__);                   \
                        spin_unlock_irqrestore(&trace_iocg_path_lock, flags);   \
                }                                                               \
        } while (0)

#else   /* CONFIG_TRACE_POINTS */
#define TRACE_IOCG_PATH(type, iocg, ...)        do { } while (0)
#endif  /* CONFIG_TRACE_POINTS */

enum {
        MILLION                 = 1000000,

        /* timer period is calculated from latency requirements, bound it */
        MIN_PERIOD              = USEC_PER_MSEC,
        MAX_PERIOD              = USEC_PER_SEC,

        /*
         * A cgroup's vtime can run 50% behind the device vtime, which
         * serves as its IO credit buffer.  Surplus weight adjustment is
         * immediately canceled if the vtime margin runs below 10%.
         */
        MARGIN_PCT              = 50,
        INUSE_MARGIN_PCT        = 10,

        /* Have some play in waitq timer operations */
        WAITQ_TIMER_MARGIN_PCT  = 5,

        /*
         * vtime can wrap well within a reasonable uptime when vrate is
         * consistently raised.  Don't trust recorded cgroup vtime if the
         * period counter indicates that it's older than 5mins.
         */
        VTIME_VALID_DUR         = 300 * USEC_PER_SEC,

        /*
         * Remember the past three non-zero usages and use the max for
         * surplus calculation.  Three slots guarantee that we remember one
         * full period usage from the last active stretch even after
         * partial deactivation and re-activation periods.  Don't start
         * giving away weight before collecting two data points to prevent
         * hweight adjustments based on one partial activation period.
         */
        NR_USAGE_SLOTS          = 3,
        MIN_VALID_USAGES        = 2,

        /* 1/64k is granular enough and can easily be handled w/ u32 */
        HWEIGHT_WHOLE           = 1 << 16,

        /*
         * As vtime is used to calculate the cost of each IO, it needs to
         * be fairly high precision.  For example, it should be able to
         * represent the cost of a single page worth of discard with
         * suffificient accuracy.  At the same time, it should be able to
         * represent reasonably long enough durations to be useful and
         * convenient during operation.
         *
         * 1s worth of vtime is 2^37.  This gives us both sub-nanosecond
         * granularity and days of wrap-around time even at extreme vrates.
         */
        VTIME_PER_SEC_SHIFT     = 37,
        VTIME_PER_SEC           = 1LLU << VTIME_PER_SEC_SHIFT,
        VTIME_PER_USEC          = VTIME_PER_SEC / USEC_PER_SEC,
        VTIME_PER_NSEC          = VTIME_PER_SEC / NSEC_PER_SEC,

        /* bound vrate adjustments within two orders of magnitude */
        VRATE_MIN_PPM           = 10000,        /* 1% */
        VRATE_MAX_PPM           = 100000000,    /* 10000% */

        VRATE_MIN               = VTIME_PER_USEC * VRATE_MIN_PPM / MILLION,
        VRATE_CLAMP_ADJ_PCT     = 4,

        /* if IOs end up waiting for requests, issue less */
        RQ_WAIT_BUSY_PCT        = 5,

        /* unbusy hysterisis */
        UNBUSY_THR_PCT          = 75,

        /* don't let cmds which take a very long time pin lagging for too long */
        MAX_LAGGING_PERIODS     = 10,

        /*
         * If usage% * 1.25 + 2% is lower than hweight% by more than 3%,
         * donate the surplus.
         */
        SURPLUS_SCALE_PCT       = 125,                  /* * 125% */
        SURPLUS_SCALE_ABS       = HWEIGHT_WHOLE / 50,   /* + 2% */
        SURPLUS_MIN_ADJ_DELTA   = HWEIGHT_WHOLE / 33,   /* 3% */

        /* switch iff the conditions are met for longer than this */
        AUTOP_CYCLE_NSEC        = 10LLU * NSEC_PER_SEC,

        /*
         * Count IO size in 4k pages.  The 12bit shift helps keeping
         * size-proportional components of cost calculation in closer
         * numbers of digits to per-IO cost components.
         */
        IOC_PAGE_SHIFT          = 12,
        IOC_PAGE_SIZE           = 1 << IOC_PAGE_SHIFT,
        IOC_SECT_TO_PAGE_SHIFT  = IOC_PAGE_SHIFT - SECTOR_SHIFT,

        /* if apart further than 16M, consider randio for linear model */
        LCOEF_RANDIO_PAGES      = 4096,
};

enum ioc_running {
        IOC_IDLE,
        IOC_RUNNING,
        IOC_STOP,
};

/* io.cost.qos controls including per-dev enable of the whole controller */
enum {
        QOS_ENABLE,
        QOS_CTRL,
        NR_QOS_CTRL_PARAMS,
};

/* io.cost.qos params */
enum {
        QOS_RPPM,
        QOS_RLAT,
        QOS_WPPM,
        QOS_WLAT,
        QOS_MIN,
        QOS_MAX,
        NR_QOS_PARAMS,
};

/* io.cost.model controls */
enum {
        COST_CTRL,
        COST_MODEL,
        NR_COST_CTRL_PARAMS,
};

/* builtin linear cost model coefficients */
enum {
        I_LCOEF_RBPS,
        I_LCOEF_RSEQIOPS,
        I_LCOEF_RRANDIOPS,
        I_LCOEF_WBPS,
        I_LCOEF_WSEQIOPS,
        I_LCOEF_WRANDIOPS,
        NR_I_LCOEFS,
};

enum {
        LCOEF_RPAGE,
        LCOEF_RSEQIO,
        LCOEF_RRANDIO,
        LCOEF_WPAGE,
        LCOEF_WSEQIO,
        LCOEF_WRANDIO,
        NR_LCOEFS,
};

enum {
        AUTOP_INVALID,
        AUTOP_HDD,
        AUTOP_SSD_QD1,
        AUTOP_SSD_DFL,
        AUTOP_SSD_FAST,
};

struct ioc_gq;

struct ioc_params {
        u32                             qos[NR_QOS_PARAMS];
        u64                             i_lcoefs[NR_I_LCOEFS];
        u64                             lcoefs[NR_LCOEFS];
        u32                             too_fast_vrate_pct;
        u32                             too_slow_vrate_pct;
};

struct ioc_missed {
        local_t                         nr_met;
        local_t                         nr_missed;
        u32                             last_met;
        u32                             last_missed;
};

struct ioc_pcpu_stat {
        struct ioc_missed               missed[2];

        local64_t                       rq_wait_ns;
        u64                             last_rq_wait_ns;
};

/* per device */
struct ioc {
        struct rq_qos                   rqos;

        bool                            enabled;

        struct ioc_params               params;
        u32                             period_us;
        u32                             margin_us;
        u64                             vrate_min;
        u64                             vrate_max;

        spinlock_t                      lock;
        struct timer_list               timer;
        struct list_head                active_iocgs;   /* active cgroups */
        struct ioc_pcpu_stat __percpu   *pcpu_stat;

        enum ioc_running                running;
        atomic64_t                      vtime_rate;

        seqcount_spinlock_t             period_seqcount;
        u32                             period_at;      /* wallclock starttime */
        u64                             period_at_vtime; /* vtime starttime */

        atomic64_t                      cur_period;     /* inc'd each period */
        int                             busy_level;     /* saturation history */

        u64                             inuse_margin_vtime;
        bool                            weights_updated;
        atomic_t                        hweight_gen;    /* for lazy hweights */

        u64                             autop_too_fast_at;
        u64                             autop_too_slow_at;
        int                             autop_idx;
        bool                            user_qos_params:1;
        bool                            user_cost_model:1;
};

/* per device-cgroup pair */
struct ioc_gq {
        struct blkg_policy_data         pd;
        struct ioc                      *ioc;

        /*
         * A iocg can get its weight from two sources - an explicit
         * per-device-cgroup configuration or the default weight of the
         * cgroup.  `cfg_weight` is the explicit per-device-cgroup
         * configuration.  `weight` is the effective considering both
         * sources.
         *
         * When an idle cgroup becomes active its `active` goes from 0 to
         * `weight`.  `inuse` is the surplus adjusted active weight.
         * `active` and `inuse` are used to calculate `hweight_active` and
         * `hweight_inuse`.
         *
         * `last_inuse` remembers `inuse` while an iocg is idle to persist
         * surplus adjustments.
         */
        u32                             cfg_weight;
        u32                             weight;
        u32                             active;
        u32                             inuse;
        u32                             last_inuse;

        sector_t                        cursor;         /* to detect randio */

        /*
         * `vtime` is this iocg's vtime cursor which progresses as IOs are
         * issued.  If lagging behind device vtime, the delta represents
         * the currently available IO budget.  If runnning ahead, the
         * overage.
         *
         * `vtime_done` is the same but progressed on completion rather
         * than issue.  The delta behind `vtime` represents the cost of
         * currently in-flight IOs.
         *
         * `last_vtime` is used to remember `vtime` at the end of the last
         * period to calculate utilization.
         */
        atomic64_t                      vtime;
        atomic64_t                      done_vtime;
        u64                             abs_vdebt;
        u64                             last_vtime;

        /*
         * The period this iocg was last active in.  Used for deactivation
         * and invalidating `vtime`.
         */
        atomic64_t                      active_period;
        struct list_head                active_list;

        /* see __propagate_weights() and current_hweight() for details */
        u64                             child_active_sum;
        u64                             child_inuse_sum;
        int                             hweight_gen;
        u32                             hweight_active;
        u32                             hweight_inuse;
        bool                            has_surplus;

        struct wait_queue_head          waitq;
        struct hrtimer                  waitq_timer;
        struct hrtimer                  delay_timer;

        /* usage is recorded as fractions of HWEIGHT_WHOLE */
        int                             usage_idx;
        u32                             usages[NR_USAGE_SLOTS];

        /* this iocg's depth in the hierarchy and ancestors including self */
        int                             level;
        struct ioc_gq                   *ancestors[];
};

/* per cgroup */
struct ioc_cgrp {
        struct blkcg_policy_data        cpd;
        unsigned int                    dfl_weight;
};

struct ioc_now {
        u64                             now_ns;
        u32                             now;
        u64                             vnow;
        u64                             vrate;
};

struct iocg_wait {
        struct wait_queue_entry         wait;
        struct bio                      *bio;
        u64                             abs_cost;
        bool                            committed;
};

struct iocg_wake_ctx {
        struct ioc_gq                   *iocg;
        u32                             hw_inuse;
        s64                             vbudget;
};

static const struct ioc_params autop[] = {
        [AUTOP_HDD] = {
                .qos                            = {
                        [QOS_RLAT]              =        250000, /* 250ms */
                        [QOS_WLAT]              =        250000,
                        [QOS_MIN]               = VRATE_MIN_PPM,
                        [QOS_MAX]               = VRATE_MAX_PPM,
                },
                .i_lcoefs                       = {
                        [I_LCOEF_RBPS]          =     174019176,
                        [I_LCOEF_RSEQIOPS]      =         41708,
                        [I_LCOEF_RRANDIOPS]     =           370,
                        [I_LCOEF_WBPS]          =     178075866,
                        [I_LCOEF_WSEQIOPS]      =         42705,
                        [I_LCOEF_WRANDIOPS]     =           378,
                },
        },
        [AUTOP_SSD_QD1] = {
                .qos                            = {
                        [QOS_RLAT]              =         25000, /* 25ms */
                        [QOS_WLAT]              =         25000,
                        [QOS_MIN]               = VRATE_MIN_PPM,
                        [QOS_MAX]               = VRATE_MAX_PPM,
                },
                .i_lcoefs                       = {
                        [I_LCOEF_RBPS]          =     245855193,
                        [I_LCOEF_RSEQIOPS]      =         61575,
                        [I_LCOEF_RRANDIOPS]     =          6946,
                        [I_LCOEF_WBPS]          =     141365009,
                        [I_LCOEF_WSEQIOPS]      =         33716,
                        [I_LCOEF_WRANDIOPS]     =         26796,
                },
        },
        [AUTOP_SSD_DFL] = {
                .qos                            = {
                        [QOS_RLAT]              =         25000, /* 25ms */
                        [QOS_WLAT]              =         25000,
                        [QOS_MIN]               = VRATE_MIN_PPM,
                        [QOS_MAX]               = VRATE_MAX_PPM,
                },
                .i_lcoefs                       = {
                        [I_LCOEF_RBPS]          =     488636629,
                        [I_LCOEF_RSEQIOPS]      =          8932,
                        [I_LCOEF_RRANDIOPS]     =          8518,
                        [I_LCOEF_WBPS]          =     427891549,
                        [I_LCOEF_WSEQIOPS]      =         28755,
                        [I_LCOEF_WRANDIOPS]     =         21940,
                },
                .too_fast_vrate_pct             =           500,
        },
        [AUTOP_SSD_FAST] = {
                .qos                            = {
                        [QOS_RLAT]              =          5000, /* 5ms */
                        [QOS_WLAT]              =          5000,
                        [QOS_MIN]               = VRATE_MIN_PPM,
                        [QOS_MAX]               = VRATE_MAX_PPM,
                },
                .i_lcoefs                       = {
                        [I_LCOEF_RBPS]          =    3102524156LLU,
                        [I_LCOEF_RSEQIOPS]      =        724816,
                        [I_LCOEF_RRANDIOPS]     =        778122,
                        [I_LCOEF_WBPS]          =    1742780862LLU,
                        [I_LCOEF_WSEQIOPS]      =        425702,
                        [I_LCOEF_WRANDIOPS]     =        443193,
                },
                .too_slow_vrate_pct             =            10,
        },
};

/*
 * vrate adjust percentages indexed by ioc->busy_level.  We adjust up on
 * vtime credit shortage and down on device saturation.
 */
static u32 vrate_adj_pct[] =
        { 0, 0, 0, 0,
          1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
          2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
          4, 4, 4, 4, 4, 4, 4, 4, 8, 8, 8, 8, 8, 8, 8, 8, 16 };

static struct blkcg_policy blkcg_policy_iocost;

/* accessors and helpers */
static struct ioc *rqos_to_ioc(struct rq_qos *rqos)
{
        return container_of(rqos, struct ioc, rqos);
}

static struct ioc *q_to_ioc(struct request_queue *q)
{
        return rqos_to_ioc(rq_qos_id(q, RQ_QOS_COST));
}

static const char *q_name(struct request_queue *q)
{
        if (test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags))
                return kobject_name(q->kobj.parent);
        else
                return "<unknown>";
}

static const char __maybe_unused *ioc_name(struct ioc *ioc)
{
        return q_name(ioc->rqos.q);
}

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

static struct ioc_gq *blkg_to_iocg(struct blkcg_gq *blkg)
{
        return pd_to_iocg(blkg_to_pd(blkg, &blkcg_policy_iocost));
}

static struct blkcg_gq *iocg_to_blkg(struct ioc_gq *iocg)
{
        return pd_to_blkg(&iocg->pd);
}

static struct ioc_cgrp *blkcg_to_iocc(struct blkcg *blkcg)
{
        return container_of(blkcg_to_cpd(blkcg, &blkcg_policy_iocost),
                            struct ioc_cgrp, cpd);
}

/*
 * Scale @abs_cost to the inverse of @hw_inuse.  The lower the hierarchical
 * weight, the more expensive each IO.  Must round up.
 */
static u64 abs_cost_to_cost(u64 abs_cost, u32 hw_inuse)
{
        return DIV64_U64_ROUND_UP(abs_cost * HWEIGHT_WHOLE, hw_inuse);
}

/*
 * The inverse of abs_cost_to_cost().  Must round up.
 */
static u64 cost_to_abs_cost(u64 cost, u32 hw_inuse)
{
        return DIV64_U64_ROUND_UP(cost * hw_inuse, HWEIGHT_WHOLE);
}

static void iocg_commit_bio(struct ioc_gq *iocg, struct bio *bio, u64 cost)
{
        bio->bi_iocost_cost = cost;
        atomic64_add(cost, &iocg->vtime);
}

#define CREATE_TRACE_POINTS
#include <trace/events/iocost.h>

/* latency Qos params changed, update period_us and all the dependent params */
static void ioc_refresh_period_us(struct ioc *ioc)
{
        u32 ppm, lat, multi, period_us;

        lockdep_assert_held(&ioc->lock);

        /* pick the higher latency target */
        if (ioc->params.qos[QOS_RLAT] >= ioc->params.qos[QOS_WLAT]) {
                ppm = ioc->params.qos[QOS_RPPM];
                lat = ioc->params.qos[QOS_RLAT];
        } else {
                ppm = ioc->params.qos[QOS_WPPM];
                lat = ioc->params.qos[QOS_WLAT];
        }

        /*
         * We want the period to be long enough to contain a healthy number
         * of IOs while short enough for granular control.  Define it as a
         * multiple of the latency target.  Ideally, the multiplier should
         * be scaled according to the percentile so that it would nominally
         * contain a certain number of requests.  Let's be simpler and
         * scale it linearly so that it's 2x >= pct(90) and 10x at pct(50).
         */
        if (ppm)
                multi = max_t(u32, (MILLION - ppm) / 50000, 2);
        else
                multi = 2;
        period_us = multi * lat;
        period_us = clamp_t(u32, period_us, MIN_PERIOD, MAX_PERIOD);

        /* calculate dependent params */
        ioc->period_us = period_us;
        ioc->margin_us = period_us * MARGIN_PCT / 100;
        ioc->inuse_margin_vtime = DIV64_U64_ROUND_UP(
                        period_us * VTIME_PER_USEC * INUSE_MARGIN_PCT, 100);
}

static int ioc_autop_idx(struct ioc *ioc)
{
        int idx = ioc->autop_idx;
        const struct ioc_params *p = &autop[idx];
        u32 vrate_pct;
        u64 now_ns;

        /* rotational? */
        if (!blk_queue_nonrot(ioc->rqos.q))
                return AUTOP_HDD;

        /* handle SATA SSDs w/ broken NCQ */
        if (blk_queue_depth(ioc->rqos.q) == 1)
                return AUTOP_SSD_QD1;

        /* use one of the normal ssd sets */
        if (idx < AUTOP_SSD_DFL)
                return AUTOP_SSD_DFL;

        /* if user is overriding anything, maintain what was there */
        if (ioc->user_qos_params || ioc->user_cost_model)
                return idx;

        /* step up/down based on the vrate */
        vrate_pct = div64_u64(atomic64_read(&ioc->vtime_rate) * 100,
                              VTIME_PER_USEC);
        now_ns = ktime_get_ns();

        if (p->too_fast_vrate_pct && p->too_fast_vrate_pct <= vrate_pct) {
                if (!ioc->autop_too_fast_at)
                        ioc->autop_too_fast_at = now_ns;
                if (now_ns - ioc->autop_too_fast_at >= AUTOP_CYCLE_NSEC)
                        return idx + 1;
        } else {
                ioc->autop_too_fast_at = 0;
        }

        if (p->too_slow_vrate_pct && p->too_slow_vrate_pct >= vrate_pct) {
                if (!ioc->autop_too_slow_at)
                        ioc->autop_too_slow_at = now_ns;
                if (now_ns - ioc->autop_too_slow_at >= AUTOP_CYCLE_NSEC)
                        return idx - 1;
        } else {
                ioc->autop_too_slow_at = 0;
        }

        return idx;
}

/*
 * Take the followings as input
 *
 *  @bps        maximum sequential throughput
 *  @seqiops    maximum sequential 4k iops
 *  @randiops   maximum random 4k iops
 *
 * and calculate the linear model cost coefficients.
 *
 *  *@page      per-page cost           1s / (@bps / 4096)
 *  *@seqio     base cost of a seq IO   max((1s / @seqiops) - *@page, 0)
 *  @randiops   base cost of a rand IO  max((1s / @randiops) - *@page, 0)
 */
static void calc_lcoefs(u64 bps, u64 seqiops, u64 randiops,
                        u64 *page, u64 *seqio, u64 *randio)
{
        u64 v;

        *page = *seqio = *randio = 0;

        if (bps)
                *page = DIV64_U64_ROUND_UP(VTIME_PER_SEC,
                                           DIV_ROUND_UP_ULL(bps, IOC_PAGE_SIZE));

        if (seqiops) {
                v = DIV64_U64_ROUND_UP(VTIME_PER_SEC, seqiops);
                if (v > *page)
                        *seqio = v - *page;
        }

        if (randiops) {
                v = DIV64_U64_ROUND_UP(VTIME_PER_SEC, randiops);
                if (v > *page)
                        *randio = v - *page;
        }
}

static void ioc_refresh_lcoefs(struct ioc *ioc)
{
        u64 *u = ioc->params.i_lcoefs;
        u64 *c = ioc->params.lcoefs;

        calc_lcoefs(u[I_LCOEF_RBPS], u[I_LCOEF_RSEQIOPS], u[I_LCOEF_RRANDIOPS],
                    &c[LCOEF_RPAGE], &c[LCOEF_RSEQIO], &c[LCOEF_RRANDIO]);
        calc_lcoefs(u[I_LCOEF_WBPS], u[I_LCOEF_WSEQIOPS], u[I_LCOEF_WRANDIOPS],
                    &c[LCOEF_WPAGE], &c[LCOEF_WSEQIO], &c[LCOEF_WRANDIO]);
}

static bool ioc_refresh_params(struct ioc *ioc, bool force)
{
        const struct ioc_params *p;
        int idx;

        lockdep_assert_held(&ioc->lock);

        idx = ioc_autop_idx(ioc);
        p = &autop[idx];

        if (idx == ioc->autop_idx && !force)
                return false;

        if (idx != ioc->autop_idx)
                atomic64_set(&ioc->vtime_rate, VTIME_PER_USEC);

        ioc->autop_idx = idx;
        ioc->autop_too_fast_at = 0;
        ioc->autop_too_slow_at = 0;

        if (!ioc->user_qos_params)
                memcpy(ioc->params.qos, p->qos, sizeof(p->qos));
        if (!ioc->user_cost_model)
                memcpy(ioc->params.i_lcoefs, p->i_lcoefs, sizeof(p->i_lcoefs));

        ioc_refresh_period_us(ioc);
        ioc_refresh_lcoefs(ioc);

        ioc->vrate_min = DIV64_U64_ROUND_UP((u64)ioc->params.qos[QOS_MIN] *
                                            VTIME_PER_USEC, MILLION);
        ioc->vrate_max = div64_u64((u64)ioc->params.qos[QOS_MAX] *
                                   VTIME_PER_USEC, MILLION);

        return true;
}

/* take a snapshot of the current [v]time and vrate */
static void ioc_now(struct ioc *ioc, struct ioc_now *now)
{
        unsigned seq;

        now->now_ns = ktime_get();
        now->now = ktime_to_us(now->now_ns);
        now->vrate = atomic64_read(&ioc->vtime_rate);

        /*
         * The current vtime is
         *
         *   vtime at period start + (wallclock time since the start) * vrate
         *
         * As a consistent snapshot of `period_at_vtime` and `period_at` is
         * needed, they're seqcount protected.
         */
        do {
                seq = read_seqcount_begin(&ioc->period_seqcount);
                now->vnow = ioc->period_at_vtime +
                        (now->now - ioc->period_at) * now->vrate;
        } while (read_seqcount_retry(&ioc->period_seqcount, seq));
}

static void ioc_start_period(struct ioc *ioc, struct ioc_now *now)
{
        WARN_ON_ONCE(ioc->running != IOC_RUNNING);

        write_seqcount_begin(&ioc->period_seqcount);
        ioc->period_at = now->now;
        ioc->period_at_vtime = now->vnow;
        write_seqcount_end(&ioc->period_seqcount);

        ioc->timer.expires = jiffies + usecs_to_jiffies(ioc->period_us);
        add_timer(&ioc->timer);
}

/*
 * Update @iocg's `active` and `inuse` to @active and @inuse, update level
 * weight sums and propagate upwards accordingly.
 */
static void __propagate_weights(struct ioc_gq *iocg, u32 active, u32 inuse)
{
        struct ioc *ioc = iocg->ioc;
        int lvl;

        lockdep_assert_held(&ioc->lock);

        inuse = clamp_t(u32, inuse, 1, active);

        if (active == iocg->active && inuse == iocg->inuse)
                return;

        for (lvl = iocg->level - 1; lvl >= 0; lvl--) {
                struct ioc_gq *parent = iocg->ancestors[lvl];
                struct ioc_gq *child = iocg->ancestors[lvl + 1];
                u32 parent_active = 0, parent_inuse = 0;

                /* update the level sums */
                parent->child_active_sum += (s32)(active - child->active);
                parent->child_inuse_sum += (s32)(inuse - child->inuse);
                /* apply the udpates */
                child->active = active;
                child->inuse = inuse;

                /*
                 * The delta between inuse and active sums indicates that
                 * that much of weight is being given away.  Parent's inuse
                 * and active should reflect the ratio.
                 */
                if (parent->child_active_sum) {
                        parent_active = parent->weight;
                        parent_inuse = DIV64_U64_ROUND_UP(
                                parent_active * parent->child_inuse_sum,
                                parent->child_active_sum);
                }

                /* do we need to keep walking up? */
                if (parent_active == parent->active &&
                    parent_inuse == parent->inuse)
                        break;

                active = parent_active;
                inuse = parent_inuse;
        }

        ioc->weights_updated = true;
}

static void commit_weights(struct ioc *ioc)
{
        lockdep_assert_held(&ioc->lock);

        if (ioc->weights_updated) {
                /* paired with rmb in current_hweight(), see there */
                smp_wmb();
                atomic_inc(&ioc->hweight_gen);
                ioc->weights_updated = false;
        }
}

static void propagate_weights(struct ioc_gq *iocg, u32 active, u32 inuse)
{
        __propagate_weights(iocg, active, inuse);
        commit_weights(iocg->ioc);
}

static void current_hweight(struct ioc_gq *iocg, u32 *hw_activep, u32 *hw_inusep)
{
        struct ioc *ioc = iocg->ioc;
        int lvl;
        u32 hwa, hwi;
        int ioc_gen;

        /* hot path - if uptodate, use cached */
        ioc_gen = atomic_read(&ioc->hweight_gen);
        if (ioc_gen == iocg->hweight_gen)
                goto out;

        /*
         * Paired with wmb in commit_weights(). If we saw the updated
         * hweight_gen, all the weight updates from __propagate_weights() are
         * visible too.
         *
         * We can race with weight updates during calculation and get it
         * wrong.  However, hweight_gen would have changed and a future
         * reader will recalculate and we're guaranteed to discard the
         * wrong result soon.
         */
        smp_rmb();

        hwa = hwi = HWEIGHT_WHOLE;
        for (lvl = 0; lvl <= iocg->level - 1; lvl++) {
                struct ioc_gq *parent = iocg->ancestors[lvl];
                struct ioc_gq *child = iocg->ancestors[lvl + 1];
                u32 active_sum = READ_ONCE(parent->child_active_sum);
                u32 inuse_sum = READ_ONCE(parent->child_inuse_sum);
                u32 active = READ_ONCE(child->active);
                u32 inuse = READ_ONCE(child->inuse);

                /* we can race with deactivations and either may read as zero */
                if (!active_sum || !inuse_sum)
                        continue;

                active_sum = max(active, active_sum);
                hwa = hwa * active / active_sum;        /* max 16bits * 10000 */

                inuse_sum = max(inuse, inuse_sum);
                hwi = hwi * inuse / inuse_sum;          /* max 16bits * 10000 */
        }

        iocg->hweight_active = max_t(u32, hwa, 1);
        iocg->hweight_inuse = max_t(u32, hwi, 1);
        iocg->hweight_gen = ioc_gen;
out:
        if (hw_activep)
                *hw_activep = iocg->hweight_active;
        if (hw_inusep)
                *hw_inusep = iocg->hweight_inuse;
}

static void weight_updated(struct ioc_gq *iocg)
{
        struct ioc *ioc = iocg->ioc;
        struct blkcg_gq *blkg = iocg_to_blkg(iocg);
        struct ioc_cgrp *iocc = blkcg_to_iocc(blkg->blkcg);
        u32 weight;

        lockdep_assert_held(&ioc->lock);

        weight = iocg->cfg_weight ?: iocc->dfl_weight;
        if (weight != iocg->weight && iocg->active)
                propagate_weights(iocg, weight,
                        DIV64_U64_ROUND_UP(iocg->inuse * weight, iocg->weight));
        iocg->weight = weight;
}

static bool iocg_activate(struct ioc_gq *iocg, struct ioc_now *now)
{
        struct ioc *ioc = iocg->ioc;
        u64 last_period, cur_period, max_period_delta;
        u64 vtime, vmargin, vmin;
        int i;

        /*
         * If seem to be already active, just update the stamp to tell the
         * timer that we're still active.  We don't mind occassional races.
         */
        if (!list_empty(&iocg->active_list)) {
                ioc_now(ioc, now);
                cur_period = atomic64_read(&ioc->cur_period);
                if (atomic64_read(&iocg->active_period) != cur_period)
                        atomic64_set(&iocg->active_period, cur_period);
                return true;
        }

        /* racy check on internal node IOs, treat as root level IOs */
        if (iocg->child_active_sum)
                return false;

        spin_lock_irq(&ioc->lock);

        ioc_now(ioc, now);

        /* update period */
        cur_period = atomic64_read(&ioc->cur_period);
        last_period = atomic64_read(&iocg->active_period);
        atomic64_set(&iocg->active_period, cur_period);

        /* already activated or breaking leaf-only constraint? */
        if (!list_empty(&iocg->active_list))
                goto succeed_unlock;
        for (i = iocg->level - 1; i > 0; i--)
                if (!list_empty(&iocg->ancestors[i]->active_list))
                        goto fail_unlock;

        if (iocg->child_active_sum)
                goto fail_unlock;

        /*
         * vtime may wrap when vrate is raised substantially due to
         * underestimated IO costs.  Look at the period and ignore its
         * vtime if the iocg has been idle for too long.  Also, cap the
         * budget it can start with to the margin.
         */
        max_period_delta = DIV64_U64_ROUND_UP(VTIME_VALID_DUR, ioc->period_us);
        vtime = atomic64_read(&iocg->vtime);
        vmargin = ioc->margin_us * now->vrate;
        vmin = now->vnow - vmargin;

        if (last_period + max_period_delta < cur_period ||
            time_before64(vtime, vmin)) {
                atomic64_add(vmin - vtime, &iocg->vtime);
                atomic64_add(vmin - vtime, &iocg->done_vtime);
                vtime = vmin;
        }

        /*
         * Activate, propagate weight and start period timer if not
         * running.  Reset hweight_gen to avoid accidental match from
         * wrapping.
         */
        iocg->hweight_gen = atomic_read(&ioc->hweight_gen) - 1;
        list_add(&iocg->active_list, &ioc->active_iocgs);
        propagate_weights(iocg, iocg->weight,
                          iocg->last_inuse ?: iocg->weight);

        TRACE_IOCG_PATH(iocg_activate, iocg, now,
                        last_period, cur_period, vtime);

        iocg->last_vtime = vtime;

        if (ioc->running == IOC_IDLE) {
                ioc->running = IOC_RUNNING;
                ioc_start_period(ioc, now);
        }

succeed_unlock:
        spin_unlock_irq(&ioc->lock);
        return true;

fail_unlock:
        spin_unlock_irq(&ioc->lock);
        return false;
}

static int iocg_wake_fn(struct wait_queue_entry *wq_entry, unsigned mode,
                        int flags, void *key)
{
        struct iocg_wait *wait = container_of(wq_entry, struct iocg_wait, wait);
        struct iocg_wake_ctx *ctx = (struct iocg_wake_ctx *)key;
        u64 cost = abs_cost_to_cost(wait->abs_cost, ctx->hw_inuse);

        ctx->vbudget -= cost;

        if (ctx->vbudget < 0)
                return -1;

        iocg_commit_bio(ctx->iocg, wait->bio, cost);

        /*
         * autoremove_wake_function() removes the wait entry only when it
         * actually changed the task state.  We want the wait always
         * removed.  Remove explicitly and use default_wake_function().
         */
        list_del_init(&wq_entry->entry);
        wait->committed = true;

        default_wake_function(wq_entry, mode, flags, key);
        return 0;
}

static void iocg_kick_waitq(struct ioc_gq *iocg, struct ioc_now *now)
{
        struct ioc *ioc = iocg->ioc;
        struct iocg_wake_ctx ctx = { .iocg = iocg };
        u64 margin_ns = (u64)(ioc->period_us *
                              WAITQ_TIMER_MARGIN_PCT / 100) * NSEC_PER_USEC;
        u64 vdebt, vshortage, expires, oexpires;
        s64 vbudget;
        u32 hw_inuse;

        lockdep_assert_held(&iocg->waitq.lock);

        current_hweight(iocg, NULL, &hw_inuse);
        vbudget = now->vnow - atomic64_read(&iocg->vtime);

        /* pay off debt */
        vdebt = abs_cost_to_cost(iocg->abs_vdebt, hw_inuse);
        if (vdebt && vbudget > 0) {
                u64 delta = min_t(u64, vbudget, vdebt);
                u64 abs_delta = min(cost_to_abs_cost(delta, hw_inuse),
                                    iocg->abs_vdebt);

                atomic64_add(delta, &iocg->vtime);
                atomic64_add(delta, &iocg->done_vtime);
                iocg->abs_vdebt -= abs_delta;
        }

        /*
         * Wake up the ones which are due and see how much vtime we'll need
         * for the next one.
         */
        ctx.hw_inuse = hw_inuse;
        ctx.vbudget = vbudget - vdebt;
        __wake_up_locked_key(&iocg->waitq, TASK_NORMAL, &ctx);
        if (!waitqueue_active(&iocg->waitq))
                return;
        if (WARN_ON_ONCE(ctx.vbudget >= 0))
                return;

        /* determine next wakeup, add a quarter margin to guarantee chunking */
        vshortage = -ctx.vbudget;
        expires = now->now_ns +
                DIV64_U64_ROUND_UP(vshortage, now->vrate) * NSEC_PER_USEC;
        expires += margin_ns / 4;

        /* if already active and close enough, don't bother */
        oexpires = ktime_to_ns(hrtimer_get_softexpires(&iocg->waitq_timer));
        if (hrtimer_is_queued(&iocg->waitq_timer) &&
            abs(oexpires - expires) <= margin_ns / 4)
                return;

        hrtimer_start_range_ns(&iocg->waitq_timer, ns_to_ktime(expires),
                               margin_ns / 4, HRTIMER_MODE_ABS);
}

static enum hrtimer_restart iocg_waitq_timer_fn(struct hrtimer *timer)
{
        struct ioc_gq *iocg = container_of(timer, struct ioc_gq, waitq_timer);
        struct ioc_now now;
        unsigned long flags;

        ioc_now(iocg->ioc, &now);

        spin_lock_irqsave(&iocg->waitq.lock, flags);
        iocg_kick_waitq(iocg, &now);
        spin_unlock_irqrestore(&iocg->waitq.lock, flags);

        return HRTIMER_NORESTART;
}

static bool iocg_kick_delay(struct ioc_gq *iocg, struct ioc_now *now)
{
        struct ioc *ioc = iocg->ioc;
        struct blkcg_gq *blkg = iocg_to_blkg(iocg);
        u64 vtime = atomic64_read(&iocg->vtime);
        u64 vmargin = ioc->margin_us * now->vrate;
        u64 margin_ns = ioc->margin_us * NSEC_PER_USEC;
        u64 delta_ns, expires, oexpires;
        u32 hw_inuse;

        lockdep_assert_held(&iocg->waitq.lock);

        /* debt-adjust vtime */
        current_hweight(iocg, NULL, &hw_inuse);
        vtime += abs_cost_to_cost(iocg->abs_vdebt, hw_inuse);

        /*
         * Clear or maintain depending on the overage. Non-zero vdebt is what
         * guarantees that @iocg is online and future iocg_kick_delay() will
         * clear use_delay. Don't leave it on when there's no vdebt.
         */
        if (!iocg->abs_vdebt || time_before_eq64(vtime, now->vnow)) {
                blkcg_clear_delay(blkg);
                return false;
        }
        if (!atomic_read(&blkg->use_delay) &&
            time_before_eq64(vtime, now->vnow + vmargin))
                return false;

        /* use delay */
        delta_ns = DIV64_U64_ROUND_UP(vtime - now->vnow,
                                      now->vrate) * NSEC_PER_USEC;
        blkcg_set_delay(blkg, delta_ns);
        expires = now->now_ns + delta_ns;

        /* if already active and close enough, don't bother */
        oexpires = ktime_to_ns(hrtimer_get_softexpires(&iocg->delay_timer));
        if (hrtimer_is_queued(&iocg->delay_timer) &&
            abs(oexpires - expires) <= margin_ns / 4)
                return true;

        hrtimer_start_range_ns(&iocg->delay_timer, ns_to_ktime(expires),
                               margin_ns / 4, HRTIMER_MODE_ABS);
        return true;
}

static enum hrtimer_restart iocg_delay_timer_fn(struct hrtimer *timer)
{
        struct ioc_gq *iocg = container_of(timer, struct ioc_gq, delay_timer);
        struct ioc_now now;
        unsigned long flags;

        spin_lock_irqsave(&iocg->waitq.lock, flags);
        ioc_now(iocg->ioc, &now);
        iocg_kick_delay(iocg, &now);
        spin_unlock_irqrestore(&iocg->waitq.lock, flags);

        return HRTIMER_NORESTART;
}

static void ioc_lat_stat(struct ioc *ioc, u32 *missed_ppm_ar, u32 *rq_wait_pct_p)
{
        u32 nr_met[2] = { };
        u32 nr_missed[2] = { };
        u64 rq_wait_ns = 0;
        int cpu, rw;

        for_each_online_cpu(cpu) {
                struct ioc_pcpu_stat *stat = per_cpu_ptr(ioc->pcpu_stat, cpu);
                u64 this_rq_wait_ns;

                for (rw = READ; rw <= WRITE; rw++) {
                        u32 this_met = local_read(&stat->missed[rw].nr_met);
                        u32 this_missed = local_read(&stat->missed[rw].nr_missed);

                        nr_met[rw] += this_met - stat->missed[rw].last_met;
                        nr_missed[rw] += this_missed - stat->missed[rw].last_missed;
                        stat->missed[rw].last_met = this_met;
                        stat->missed[rw].last_missed = this_missed;
                }

                this_rq_wait_ns = local64_read(&stat->rq_wait_ns);
                rq_wait_ns += this_rq_wait_ns - stat->last_rq_wait_ns;
                stat->last_rq_wait_ns = this_rq_wait_ns;
        }

        for (rw = READ; rw <= WRITE; rw++) {
                if (nr_met[rw] + nr_missed[rw])
                        missed_ppm_ar[rw] =
                                DIV64_U64_ROUND_UP((u64)nr_missed[rw] * MILLION,
                                                   nr_met[rw] + nr_missed[rw]);
                else
                        missed_ppm_ar[rw] = 0;
        }

        *rq_wait_pct_p = div64_u64(rq_wait_ns * 100,
                                   ioc->period_us * NSEC_PER_USEC);
}

/* was iocg idle this period? */
static bool iocg_is_idle(struct ioc_gq *iocg)
{
        struct ioc *ioc = iocg->ioc;

        /* did something get issued this period? */
        if (atomic64_read(&iocg->active_period) ==
            atomic64_read(&ioc->cur_period))
                return false;

        /* is something in flight? */
        if (atomic64_read(&iocg->done_vtime) != atomic64_read(&iocg->vtime))
                return false;

        return true;
}

/* returns usage with margin added if surplus is large enough */
static u32 surplus_adjusted_hweight_inuse(u32 usage, u32 hw_inuse)
{
        /* add margin */
        usage = DIV_ROUND_UP(usage * SURPLUS_SCALE_PCT, 100);
        usage += SURPLUS_SCALE_ABS;

        /* don't bother if the surplus is too small */
        if (usage + SURPLUS_MIN_ADJ_DELTA > hw_inuse)
                return 0;

        return usage;
}

static void ioc_timer_fn(struct timer_list *timer)
{
        struct ioc *ioc = container_of(timer, struct ioc, timer);
        struct ioc_gq *iocg, *tiocg;
        struct ioc_now now;
        int nr_surpluses = 0, nr_shortages = 0, nr_lagging = 0;
        u32 ppm_rthr = MILLION - ioc->params.qos[QOS_RPPM];
        u32 ppm_wthr = MILLION - ioc->params.qos[QOS_WPPM];
        u32 missed_ppm[2], rq_wait_pct;
        u64 period_vtime;
        int prev_busy_level, i;

        /* how were the latencies during the period? */
        ioc_lat_stat(ioc, missed_ppm, &rq_wait_pct);

        /* take care of active iocgs */
        spin_lock_irq(&ioc->lock);

        ioc_now(ioc, &now);

        period_vtime = now.vnow - ioc->period_at_vtime;
        if (WARN_ON_ONCE(!period_vtime)) {
                spin_unlock_irq(&ioc->lock);
                return;
        }

        /*
         * Waiters determine the sleep durations based on the vrate they
         * saw at the time of sleep.  If vrate has increased, some waiters
         * could be sleeping for too long.  Wake up tardy waiters which
         * should have woken up in the last period and expire idle iocgs.
         */
        list_for_each_entry_safe(iocg, tiocg, &ioc->active_iocgs, active_list) {
                if (!waitqueue_active(&iocg->waitq) && !iocg->abs_vdebt &&
                    !iocg_is_idle(iocg))
                        continue;

                spin_lock(&iocg->waitq.lock);

                if (waitqueue_active(&iocg->waitq) || iocg->abs_vdebt) {
                        /* might be oversleeping vtime / hweight changes, kick */
                        iocg_kick_waitq(iocg, &now);
                        iocg_kick_delay(iocg, &now);
                } else if (iocg_is_idle(iocg)) {
                        /* no waiter and idle, deactivate */
                        iocg->last_inuse = iocg->inuse;
                        __propagate_weights(iocg, 0, 0);
                        list_del_init(&iocg->active_list);
                }

                spin_unlock(&iocg->waitq.lock);
        }
        commit_weights(ioc);

        /* calc usages and see whether some weights need to be moved around */
        list_for_each_entry(iocg, &ioc->active_iocgs, active_list) {
                u64 vdone, vtime, vusage, vmargin, vmin;
                u32 hw_active, hw_inuse, usage;

                /*
                 * Collect unused and wind vtime closer to vnow to prevent
                 * iocgs from accumulating a large amount of budget.
                 */
                vdone = atomic64_read(&iocg->done_vtime);
                vtime = atomic64_read(&iocg->vtime);
                current_hweight(iocg, &hw_active, &hw_inuse);

                /*
                 * Latency QoS detection doesn't account for IOs which are
                 * in-flight for longer than a period.  Detect them by
                 * comparing vdone against period start.  If lagging behind
                 * IOs from past periods, don't increase vrate.
                 */
                if ((ppm_rthr != MILLION || ppm_wthr != MILLION) &&
                    !atomic_read(&iocg_to_blkg(iocg)->use_delay) &&
                    time_after64(vtime, vdone) &&
                    time_after64(vtime, now.vnow -
                                 MAX_LAGGING_PERIODS * period_vtime) &&
                    time_before64(vdone, now.vnow - period_vtime))
                        nr_lagging++;

                if (waitqueue_active(&iocg->waitq))
                        vusage = now.vnow - iocg->last_vtime;
                else if (time_before64(iocg->last_vtime, vtime))
                        vusage = vtime - iocg->last_vtime;
                else
                        vusage = 0;

                iocg->last_vtime += vusage;
                /*
                 * Factor in in-flight vtime into vusage to avoid
                 * high-latency completions appearing as idle.  This should
                 * be done after the above ->last_time adjustment.
                 */
                vusage = max(vusage, vtime - vdone);

                /* calculate hweight based usage ratio and record */
                if (vusage) {
                        usage = DIV64_U64_ROUND_UP(vusage * hw_inuse,
                                                   period_vtime);
                        iocg->usage_idx = (iocg->usage_idx + 1) % NR_USAGE_SLOTS;
                        iocg->usages[iocg->usage_idx] = usage;
                } else {
                        usage = 0;
                }

                /* see whether there's surplus vtime */
                vmargin = ioc->margin_us * now.vrate;
                vmin = now.vnow - vmargin;

                iocg->has_surplus = false;

                if (!waitqueue_active(&iocg->waitq) &&
                    time_before64(vtime, vmin)) {
                        u64 delta = vmin - vtime;

                        /* throw away surplus vtime */
                        atomic64_add(delta, &iocg->vtime);
                        atomic64_add(delta, &iocg->done_vtime);
                        iocg->last_vtime += delta;
                        /* if usage is sufficiently low, maybe it can donate */
                        if (surplus_adjusted_hweight_inuse(usage, hw_inuse)) {
                                iocg->has_surplus = true;
                                nr_surpluses++;
                        }
                } else if (hw_inuse < hw_active) {
                        u32 new_hwi, new_inuse;

                        /* was donating but might need to take back some */
                        if (waitqueue_active(&iocg->waitq)) {
                                new_hwi = hw_active;
                        } else {
                                new_hwi = max(hw_inuse,
                                              usage * SURPLUS_SCALE_PCT / 100 +
                                              SURPLUS_SCALE_ABS);
                        }

                        new_inuse = div64_u64((u64)iocg->inuse * new_hwi,
                                              hw_inuse);
                        new_inuse = clamp_t(u32, new_inuse, 1, iocg->active);

                        if (new_inuse > iocg->inuse) {
                                TRACE_IOCG_PATH(inuse_takeback, iocg, &now,
                                                iocg->inuse, new_inuse,
                                                hw_inuse, new_hwi);
                                __propagate_weights(iocg, iocg->weight,
                                                    new_inuse);
                        }
                } else {
                        /* genuninely out of vtime */
                        nr_shortages++;
                }
        }

        if (!nr_shortages || !nr_surpluses)
                goto skip_surplus_transfers;

        /* there are both shortages and surpluses, transfer surpluses */
        list_for_each_entry(iocg, &ioc->active_iocgs, active_list) {
                u32 usage, hw_active, hw_inuse, new_hwi, new_inuse;
                int nr_valid = 0;

                if (!iocg->has_surplus)
                        continue;

                /* base the decision on max historical usage */
                for (i = 0, usage = 0; i < NR_USAGE_SLOTS; i++) {
                        if (iocg->usages[i]) {
                                usage = max(usage, iocg->usages[i]);
                                nr_valid++;
                        }
                }
                if (nr_valid < MIN_VALID_USAGES)
                        continue;

                current_hweight(iocg, &hw_active, &hw_inuse);
                new_hwi = surplus_adjusted_hweight_inuse(usage, hw_inuse);
                if (!new_hwi)
                        continue;

                new_inuse = DIV64_U64_ROUND_UP((u64)iocg->inuse * new_hwi,
                                               hw_inuse);
                if (new_inuse < iocg->inuse) {
                        TRACE_IOCG_PATH(inuse_giveaway, iocg, &now,
                                        iocg->inuse, new_inuse,
                                        hw_inuse, new_hwi);
                        __propagate_weights(iocg, iocg->weight, new_inuse);
                }
        }
skip_surplus_transfers:
        commit_weights(ioc);

        /*
         * If q is getting clogged or we're missing too much, we're issuing
         * too much IO and should lower vtime rate.  If we're not missing
         * and experiencing shortages but not surpluses, we're too stingy
         * and should increase vtime rate.
         */
        prev_busy_level = ioc->busy_level;
        if (rq_wait_pct > RQ_WAIT_BUSY_PCT ||
            missed_ppm[READ] > ppm_rthr ||
            missed_ppm[WRITE] > ppm_wthr) {
                /* clearly missing QoS targets, slow down vrate */
                ioc->busy_level = max(ioc->busy_level, 0);
                ioc->busy_level++;
        } else if (rq_wait_pct <= RQ_WAIT_BUSY_PCT * UNBUSY_THR_PCT / 100 &&
                   missed_ppm[READ] <= ppm_rthr * UNBUSY_THR_PCT / 100 &&
                   missed_ppm[WRITE] <= ppm_wthr * UNBUSY_THR_PCT / 100) {
                /* QoS targets are being met with >25% margin */
                if (nr_shortages) {
                        /*
                         * We're throttling while the device has spare
                         * capacity.  If vrate was being slowed down, stop.
                         */
                        ioc->busy_level = min(ioc->busy_level, 0);

                        /*
                         * If there are IOs spanning multiple periods, wait
                         * them out before pushing the device harder.  If
                         * there are surpluses, let redistribution work it
                         * out first.
                         */
                        if (!nr_lagging && !nr_surpluses)
                                ioc->busy_level--;
                } else {
                        /*
                         * Nobody is being throttled and the users aren't
                         * issuing enough IOs to saturate the device.  We
                         * simply don't know how close the device is to
                         * saturation.  Coast.
                         */
                        ioc->busy_level = 0;
                }
        } else {
                /* inside the hysterisis margin, we're good */
                ioc->busy_level = 0;
        }

        ioc->busy_level = clamp(ioc->busy_level, -1000, 1000);

        if (ioc->busy_level > 0 || (ioc->busy_level < 0 && !nr_lagging)) {
                u64 vrate = atomic64_read(&ioc->vtime_rate);
                u64 vrate_min = ioc->vrate_min, vrate_max = ioc->vrate_max;

                /* rq_wait signal is always reliable, ignore user vrate_min */
                if (rq_wait_pct > RQ_WAIT_BUSY_PCT)
                        vrate_min = VRATE_MIN;

                /*
                 * If vrate is out of bounds, apply clamp gradually as the
                 * bounds can change abruptly.  Otherwise, apply busy_level
                 * based adjustment.
                 */
                if (vrate < vrate_min) {
                        vrate = div64_u64(vrate * (100 + VRATE_CLAMP_ADJ_PCT),
                                          100);
                        vrate = min(vrate, vrate_min);
                } else if (vrate > vrate_max) {
                        vrate = div64_u64(vrate * (100 - VRATE_CLAMP_ADJ_PCT),
                                          100);
                        vrate = max(vrate, vrate_max);
                } else {
                        int idx = min_t(int, abs(ioc->busy_level),
                                        ARRAY_SIZE(vrate_adj_pct) - 1);
                        u32 adj_pct = vrate_adj_pct[idx];

                        if (ioc->busy_level > 0)
                                adj_pct = 100 - adj_pct;
                        else
                                adj_pct = 100 + adj_pct;

                        vrate = clamp(DIV64_U64_ROUND_UP(vrate * adj_pct, 100),
                                      vrate_min, vrate_max);
                }

                trace_iocost_ioc_vrate_adj(ioc, vrate, missed_ppm, rq_wait_pct,
                                           nr_lagging, nr_shortages,
                                           nr_surpluses);

                atomic64_set(&ioc->vtime_rate, vrate);
                ioc->inuse_margin_vtime = DIV64_U64_ROUND_UP(
                        ioc->period_us * vrate * INUSE_MARGIN_PCT, 100);
        } else if (ioc->busy_level != prev_busy_level || nr_lagging) {
                trace_iocost_ioc_vrate_adj(ioc, atomic64_read(&ioc->vtime_rate),
                                           missed_ppm, rq_wait_pct, nr_lagging,
                                           nr_shortages, nr_surpluses);
        }

        ioc_refresh_params(ioc, false);

        /*
         * This period is done.  Move onto the next one.  If nothing's
         * going on with the device, stop the timer.
         */
        atomic64_inc(&ioc->cur_period);

        if (ioc->running != IOC_STOP) {
                if (!list_empty(&ioc->active_iocgs)) {
                        ioc_start_period(ioc, &now);
                } else {
                        ioc->busy_level = 0;
                        ioc->running = IOC_IDLE;
                }
        }

        spin_unlock_irq(&ioc->lock);
}

static void calc_vtime_cost_builtin(struct bio *bio, struct ioc_gq *iocg,
                                    bool is_merge, u64 *costp)
{
        struct ioc *ioc = iocg->ioc;
        u64 coef_seqio, coef_randio, coef_page;
        u64 pages = max_t(u64, bio_sectors(bio) >> IOC_SECT_TO_PAGE_SHIFT, 1);
        u64 seek_pages = 0;
        u64 cost = 0;

        switch (bio_op(bio)) {
        case REQ_OP_READ:
                coef_seqio      = ioc->params.lcoefs[LCOEF_RSEQIO];
                coef_randio     = ioc->params.lcoefs[LCOEF_RRANDIO];
                coef_page       = ioc->params.lcoefs[LCOEF_RPAGE];
                break;
        case REQ_OP_WRITE:
                coef_seqio      = ioc->params.lcoefs[LCOEF_WSEQIO];
                coef_randio     = ioc->params.lcoefs[LCOEF_WRANDIO];
                coef_page       = ioc->params.lcoefs[LCOEF_WPAGE];
                break;
        default:
                goto out;
        }

        if (iocg->cursor) {
                seek_pages = abs(bio->bi_iter.bi_sector - iocg->cursor);
                seek_pages >>= IOC_SECT_TO_PAGE_SHIFT;
        }

        if (!is_merge) {
                if (seek_pages > LCOEF_RANDIO_PAGES) {
                        cost += coef_randio;
                } else {
                        cost += coef_seqio;
                }
        }
        cost += pages * coef_page;
out:
        *costp = cost;
}

static u64 calc_vtime_cost(struct bio *bio, struct ioc_gq *iocg, bool is_merge)
{
        u64 cost;

        calc_vtime_cost_builtin(bio, iocg, is_merge, &cost);
        return cost;
}

static void calc_size_vtime_cost_builtin(struct request *rq, struct ioc *ioc,
                                         u64 *costp)
{
        unsigned int pages = blk_rq_stats_sectors(rq) >> IOC_SECT_TO_PAGE_SHIFT;

        switch (req_op(rq)) {
        case REQ_OP_READ:
                *costp = pages * ioc->params.lcoefs[LCOEF_RPAGE];
                break;
        case REQ_OP_WRITE:
                *costp = pages * ioc->params.lcoefs[LCOEF_WPAGE];
                break;
        default:
                *costp = 0;
        }
}

static u64 calc_size_vtime_cost(struct request *rq, struct ioc *ioc)
{
        u64 cost;

        calc_size_vtime_cost_builtin(rq, ioc, &cost);
        return cost;
}

static void ioc_rqos_throttle(struct rq_qos *rqos, struct bio *bio)
{
        struct blkcg_gq *blkg = bio->bi_blkg;
        struct ioc *ioc = rqos_to_ioc(rqos);
        struct ioc_gq *iocg = blkg_to_iocg(blkg);
        struct ioc_now now;
        struct iocg_wait wait;
        u32 hw_active, hw_inuse;
        u64 abs_cost, cost, vtime;

        /* bypass IOs if disabled or for root cgroup */
        if (!ioc->enabled || !iocg->level)
                return;

        /* always activate so that even 0 cost IOs get protected to some level */
        if (!iocg_activate(iocg, &now))
                return;

        /* calculate the absolute vtime cost */
        abs_cost = calc_vtime_cost(bio, iocg, false);
        if (!abs_cost)
                return;

        iocg->cursor = bio_end_sector(bio);

        vtime = atomic64_read(&iocg->vtime);
        current_hweight(iocg, &hw_active, &hw_inuse);

        if (hw_inuse < hw_active &&
            time_after_eq64(vtime + ioc->inuse_margin_vtime, now.vnow)) {
                TRACE_IOCG_PATH(inuse_reset, iocg, &now,
                                iocg->inuse, iocg->weight, hw_inuse, hw_active);
                spin_lock_irq(&ioc->lock);
                propagate_weights(iocg, iocg->weight, iocg->weight);
                spin_unlock_irq(&ioc->lock);
                current_hweight(iocg, &hw_active, &hw_inuse);
        }

        cost = abs_cost_to_cost(abs_cost, hw_inuse);

        /*
         * If no one's waiting and within budget, issue right away.  The
         * tests are racy but the races aren't systemic - we only miss once
         * in a while which is fine.
         */
        if (!waitqueue_active(&iocg->waitq) && !iocg->abs_vdebt &&
            time_before_eq64(vtime + cost, now.vnow)) {
                iocg_commit_bio(iocg, bio, cost);
                return;
        }

        /*
         * We activated above but w/o any synchronization. Deactivation is
         * synchronized with waitq.lock and we won't get deactivated as long
         * as we're waiting or has debt, so we're good if we're activated
         * here. In the unlikely case that we aren't, just issue the IO.
         */
        spin_lock_irq(&iocg->waitq.lock);

        if (unlikely(list_empty(&iocg->active_list))) {
                spin_unlock_irq(&iocg->waitq.lock);
                iocg_commit_bio(iocg, bio, cost);
                return;
        }

        /*
         * We're over budget. If @bio has to be issued regardless, remember
         * the abs_cost instead of advancing vtime. iocg_kick_waitq() will pay
         * off the debt before waking more IOs.
         *
         * This way, the debt is continuously paid off each period with the
         * actual budget available to the cgroup. If we just wound vtime, we
         * would incorrectly use the current hw_inuse for the entire amount
         * which, for example, can lead to the cgroup staying blocked for a
         * long time even with substantially raised hw_inuse.
         *
         * An iocg with vdebt should stay online so that the timer can keep
         * deducting its vdebt and [de]activate use_delay mechanism
         * accordingly. We don't want to race against the timer trying to
         * clear them and leave @iocg inactive w/ dangling use_delay heavily
         * penalizing the cgroup and its descendants.
         */
        if (bio_issue_as_root_blkg(bio) || fatal_signal_pending(current)) {
                iocg->abs_vdebt += abs_cost;
                if (iocg_kick_delay(iocg, &now))
                        blkcg_schedule_throttle(rqos->q,
                                        (bio->bi_opf & REQ_SWAP) == REQ_SWAP);
                spin_unlock_irq(&iocg->waitq.lock);
                return;
        }

        /*
         * Append self to the waitq and schedule the wakeup timer if we're
         * the first waiter.  The timer duration is calculated based on the
         * current vrate.  vtime and hweight changes can make it too short
         * or too long.  Each wait entry records the absolute cost it's
         * waiting for to allow re-evaluation using a custom wait entry.
         *
         * If too short, the timer simply reschedules itself.  If too long,
         * the period timer will notice and trigger wakeups.
         *
         * All waiters are on iocg->waitq and the wait states are
         * synchronized using waitq.lock.
         */
        init_waitqueue_func_entry(&wait.wait, iocg_wake_fn);
        wait.wait.private = current;
        wait.bio = bio;
        wait.abs_cost = abs_cost;
        wait.committed = false; /* will be set true by waker */

        __add_wait_queue_entry_tail(&iocg->waitq, &wait.wait);
        iocg_kick_waitq(iocg, &now);

        spin_unlock_irq(&iocg->waitq.lock);

        while (true) {
                set_current_state(TASK_UNINTERRUPTIBLE);
                if (wait.committed)
                        break;
                io_schedule();
        }

        /* waker already committed us, proceed */
        finish_wait(&iocg->waitq, &wait.wait);
}

static void ioc_rqos_merge(struct rq_qos *rqos, struct request *rq,
                           struct bio *bio)
{
        struct ioc_gq *iocg = blkg_to_iocg(bio->bi_blkg);
        struct ioc *ioc = iocg->ioc;
        sector_t bio_end = bio_end_sector(bio);
        struct ioc_now now;
        u32 hw_inuse;
        u64 abs_cost, cost;
        unsigned long flags;

        /* bypass if disabled or for root cgroup */
        if (!ioc->enabled || !iocg->level)
                return;

        abs_cost = calc_vtime_cost(bio, iocg, true);
        if (!abs_cost)
                return;

        ioc_now(ioc, &now);
        current_hweight(iocg, NULL, &hw_inuse);
        cost = abs_cost_to_cost(abs_cost, hw_inuse);

        /* update cursor if backmerging into the request at the cursor */
        if (blk_rq_pos(rq) < bio_end &&
            blk_rq_pos(rq) + blk_rq_sectors(rq) == iocg->cursor)
                iocg->cursor = bio_end;

        /*
         * Charge if there's enough vtime budget and the existing request has
         * cost assigned.
         */
        if (rq->bio && rq->bio->bi_iocost_cost &&
            time_before_eq64(atomic64_read(&iocg->vtime) + cost, now.vnow)) {
                iocg_commit_bio(iocg, bio, cost);
                return;
        }

        /*
         * Otherwise, account it as debt if @iocg is online, which it should
         * be for the vast majority of cases. See debt handling in
         * ioc_rqos_throttle() for details.
         */
        spin_lock_irqsave(&iocg->waitq.lock, flags);
        if (likely(!list_empty(&iocg->active_list))) {
                iocg->abs_vdebt += abs_cost;
                iocg_kick_delay(iocg, &now);
        } else {
                iocg_commit_bio(iocg, bio, cost);
        }
        spin_unlock_irqrestore(&iocg->waitq.lock, flags);
}

static void ioc_rqos_done_bio(struct rq_qos *rqos, struct bio *bio)
{
        struct ioc_gq *iocg = blkg_to_iocg(bio->bi_blkg);

        if (iocg && bio->bi_iocost_cost)
                atomic64_add(bio->bi_iocost_cost, &iocg->done_vtime);
}

static void ioc_rqos_done(struct rq_qos *rqos, struct request *rq)
{
        struct ioc *ioc = rqos_to_ioc(rqos);
        struct ioc_pcpu_stat *ccs;
        u64 on_q_ns, rq_wait_ns, size_nsec;
        int pidx, rw;

        if (!ioc->enabled || !rq->alloc_time_ns || !rq->start_time_ns)
                return;

        switch (req_op(rq) & REQ_OP_MASK) {
        case REQ_OP_READ:
                pidx = QOS_RLAT;
                rw = READ;
                break;
        case REQ_OP_WRITE:
                pidx = QOS_WLAT;
                rw = WRITE;
                break;
        default:
                return;
        }

        on_q_ns = ktime_get_ns() - rq->alloc_time_ns;
        rq_wait_ns = rq->start_time_ns - rq->alloc_time_ns;
        size_nsec = div64_u64(calc_size_vtime_cost(rq, ioc), VTIME_PER_NSEC);

        ccs = get_cpu_ptr(ioc->pcpu_stat);

        if (on_q_ns <= size_nsec ||
            on_q_ns - size_nsec <= ioc->params.qos[pidx] * NSEC_PER_USEC)
                local_inc(&ccs->missed[rw].nr_met);
        else
                local_inc(&ccs->missed[rw].nr_missed);

        local64_add(rq_wait_ns, &ccs->rq_wait_ns);

        put_cpu_ptr(ccs);
}

static void ioc_rqos_queue_depth_changed(struct rq_qos *rqos)
{
        struct ioc *ioc = rqos_to_ioc(rqos);

        spin_lock_irq(&ioc->lock);
        ioc_refresh_params(ioc, false);
        spin_unlock_irq(&ioc->lock);
}

static void ioc_rqos_exit(struct rq_qos *rqos)
{
        struct ioc *ioc = rqos_to_ioc(rqos);

        blkcg_deactivate_policy(rqos->q, &blkcg_policy_iocost);

        spin_lock_irq(&ioc->lock);
        ioc->running = IOC_STOP;
        spin_unlock_irq(&ioc->lock);

        del_timer_sync(&ioc->timer);
        free_percpu(ioc->pcpu_stat);
        kfree(ioc);
}

static struct rq_qos_ops ioc_rqos_ops = {
        .throttle = ioc_rqos_throttle,
        .merge = ioc_rqos_merge,
        .done_bio = ioc_rqos_done_bio,
        .done = ioc_rqos_done,
        .queue_depth_changed = ioc_rqos_queue_depth_changed,
        .exit = ioc_rqos_exit,
};

static int blk_iocost_init(struct request_queue *q)
{
        struct ioc *ioc;
        struct rq_qos *rqos;
        int i, cpu, ret;

        ioc = kzalloc(sizeof(*ioc), GFP_KERNEL);
        if (!ioc)
                return -ENOMEM;

        ioc->pcpu_stat = alloc_percpu(struct ioc_pcpu_stat);
        if (!ioc->pcpu_stat) {
                kfree(ioc);
                return -ENOMEM;
        }

        for_each_possible_cpu(cpu) {
                struct ioc_pcpu_stat *ccs = per_cpu_ptr(ioc->pcpu_stat, cpu);

                for (i = 0; i < ARRAY_SIZE(ccs->missed); i++) {
                        local_set(&ccs->missed[i].nr_met, 0);
                        local_set(&ccs->missed[i].nr_missed, 0);
                }
                local64_set(&ccs->rq_wait_ns, 0);
        }

        rqos = &ioc->rqos;
        rqos->id = RQ_QOS_COST;
        rqos->ops = &ioc_rqos_ops;
        rqos->q = q;

        spin_lock_init(&ioc->lock);
        timer_setup(&ioc->timer, ioc_timer_fn, 0);
        INIT_LIST_HEAD(&ioc->active_iocgs);

        ioc->running = IOC_IDLE;
        atomic64_set(&ioc->vtime_rate, VTIME_PER_USEC);
        seqcount_spinlock_init(&ioc->period_seqcount, &ioc->lock);
        ioc->period_at = ktime_to_us(ktime_get());
        atomic64_set(&ioc->cur_period, 0);
        atomic_set(&ioc->hweight_gen, 0);

        spin_lock_irq(&ioc->lock);
        ioc->autop_idx = AUTOP_INVALID;
        ioc_refresh_params(ioc, true);
        spin_unlock_irq(&ioc->lock);

        rq_qos_add(q, rqos);
        ret = blkcg_activate_policy(q, &blkcg_policy_iocost);
        if (ret) {
                rq_qos_del(q, rqos);
                free_percpu(ioc->pcpu_stat);
                kfree(ioc);
                return ret;
        }
        return 0;
}

static struct blkcg_policy_data *ioc_cpd_alloc(gfp_t gfp)
{
        struct ioc_cgrp *iocc;

        iocc = kzalloc(sizeof(struct ioc_cgrp), gfp);
        if (!iocc)
                return NULL;

        iocc->dfl_weight = CGROUP_WEIGHT_DFL;
        return &iocc->cpd;
}

static void ioc_cpd_free(struct blkcg_policy_data *cpd)
{
        kfree(container_of(cpd, struct ioc_cgrp, cpd));
}

static struct blkg_policy_data *ioc_pd_alloc(gfp_t gfp, struct request_queue *q,
                                             struct blkcg *blkcg)
{
        int levels = blkcg->css.cgroup->level + 1;
        struct ioc_gq *iocg;

        iocg = kzalloc_node(struct_size(iocg, ancestors, levels), gfp, q->node);
        if (!iocg)
                return NULL;

        return &iocg->pd;
}

static void ioc_pd_init(struct blkg_policy_data *pd)
{
        struct ioc_gq *iocg = pd_to_iocg(pd);
        struct blkcg_gq *blkg = pd_to_blkg(&iocg->pd);
        struct ioc *ioc = q_to_ioc(blkg->q);
        struct ioc_now now;
        struct blkcg_gq *tblkg;
        unsigned long flags;

        ioc_now(ioc, &now);

        iocg->ioc = ioc;
        atomic64_set(&iocg->vtime, now.vnow);
        atomic64_set(&iocg->done_vtime, now.vnow);
        atomic64_set(&iocg->active_period, atomic64_read(&ioc->cur_period));
        INIT_LIST_HEAD(&iocg->active_list);
        iocg->hweight_active = HWEIGHT_WHOLE;
        iocg->hweight_inuse = HWEIGHT_WHOLE;

        init_waitqueue_head(&iocg->waitq);
        hrtimer_init(&iocg->waitq_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
        iocg->waitq_timer.function = iocg_waitq_timer_fn;
        hrtimer_init(&iocg->delay_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
        iocg->delay_timer.function = iocg_delay_timer_fn;

        iocg->level = blkg->blkcg->css.cgroup->level;

        for (tblkg = blkg; tblkg; tblkg = tblkg->parent) {
                struct ioc_gq *tiocg = blkg_to_iocg(tblkg);
                iocg->ancestors[tiocg->level] = tiocg;
        }

        spin_lock_irqsave(&ioc->lock, flags);
        weight_updated(iocg);
        spin_unlock_irqrestore(&ioc->lock, flags);
}

static void ioc_pd_free(struct blkg_policy_data *pd)
{
        struct ioc_gq *iocg = pd_to_iocg(pd);
        struct ioc *ioc = iocg->ioc;
        unsigned long flags;

        if (ioc) {
                spin_lock_irqsave(&ioc->lock, flags);
                if (!list_empty(&iocg->active_list)) {
                        propagate_weights(iocg, 0, 0);
                        list_del_init(&iocg->active_list);
                }
                spin_unlock_irqrestore(&ioc->lock, flags);

                hrtimer_cancel(&iocg->waitq_timer);
                hrtimer_cancel(&iocg->delay_timer);
        }
        kfree(iocg);
}

static u64 ioc_weight_prfill(struct seq_file *sf, struct blkg_policy_data *pd,
                             int off)
{
        const char *dname = blkg_dev_name(pd->blkg);
        struct ioc_gq *iocg = pd_to_iocg(pd);

        if (dname && iocg->cfg_weight)
                seq_printf(sf, "%s %u\n", dname, iocg->cfg_weight);
        return 0;
}


static int ioc_weight_show(struct seq_file *sf, void *v)
{
        struct blkcg *blkcg = css_to_blkcg(seq_css(sf));
        struct ioc_cgrp *iocc = blkcg_to_iocc(blkcg);

        seq_printf(sf, "default %u\n", iocc->dfl_weight);
        blkcg_print_blkgs(sf, blkcg, ioc_weight_prfill,
                          &blkcg_policy_iocost, seq_cft(sf)->private, false);
        return 0;
}

static ssize_t ioc_weight_write(struct kernfs_open_file *of, char *buf,
                                size_t nbytes, loff_t off)
{
        struct blkcg *blkcg = css_to_blkcg(of_css(of));
        struct ioc_cgrp *iocc = blkcg_to_iocc(blkcg);
        struct blkg_conf_ctx ctx;
        struct ioc_gq *iocg;
        u32 v;
        int ret;

        if (!strchr(buf, ':')) {
                struct blkcg_gq *blkg;

                if (!sscanf(buf, "default %u", &v) && !sscanf(buf, "%u", &v))
                        return -EINVAL;

                if (v < CGROUP_WEIGHT_MIN || v > CGROUP_WEIGHT_MAX)
                        return -EINVAL;

                spin_lock(&blkcg->lock);
                iocc->dfl_weight = v;
                hlist_for_each_entry(blkg, &blkcg->blkg_list, blkcg_node) {
                        struct ioc_gq *iocg = blkg_to_iocg(blkg);

                        if (iocg) {
                                spin_lock_irq(&iocg->ioc->lock);
                                weight_updated(iocg);
                                spin_unlock_irq(&iocg->ioc->lock);
                        }
                }
                spin_unlock(&blkcg->lock);

                return nbytes;
        }

        ret = blkg_conf_prep(blkcg, &blkcg_policy_iocost, buf, &ctx);
        if (ret)
                return ret;

        iocg = blkg_to_iocg(ctx.blkg);

        if (!strncmp(ctx.body, "default", 7)) {
                v = 0;
        } else {
                if (!sscanf(ctx.body, "%u", &v))
                        goto einval;
                if (v < CGROUP_WEIGHT_MIN || v > CGROUP_WEIGHT_MAX)
                        goto einval;
        }

        spin_lock(&iocg->ioc->lock);
        iocg->cfg_weight = v;
        weight_updated(iocg);
        spin_unlock(&iocg->ioc->lock);

        blkg_conf_finish(&ctx);
        return nbytes;

einval:
        blkg_conf_finish(&ctx);
        return -EINVAL;
}

static u64 ioc_qos_prfill(struct seq_file *sf, struct blkg_policy_data *pd,
                          int off)
{
        const char *dname = blkg_dev_name(pd->blkg);
        struct ioc *ioc = pd_to_iocg(pd)->ioc;

        if (!dname)
                return 0;

        seq_printf(sf, "%s enable=%d ctrl=%s rpct=%u.%02u rlat=%u wpct=%u.%02u wlat=%u min=%u.%02u max=%u.%02u\n",
                   dname, ioc->enabled, ioc->user_qos_params ? "user" : "auto",
                   ioc->params.qos[QOS_RPPM] / 10000,
                   ioc->params.qos[QOS_RPPM] % 10000 / 100,
                   ioc->params.qos[QOS_RLAT],
                   ioc->params.qos[QOS_WPPM] / 10000,
                   ioc->params.qos[QOS_WPPM] % 10000 / 100,
                   ioc->params.qos[QOS_WLAT],
                   ioc->params.qos[QOS_MIN] / 10000,
                   ioc->params.qos[QOS_MIN] % 10000 / 100,
                   ioc->params.qos[QOS_MAX] / 10000,
                   ioc->params.qos[QOS_MAX] % 10000 / 100);
        return 0;
}

static int ioc_qos_show(struct seq_file *sf, void *v)
{
        struct blkcg *blkcg = css_to_blkcg(seq_css(sf));

        blkcg_print_blkgs(sf, blkcg, ioc_qos_prfill,
                          &blkcg_policy_iocost, seq_cft(sf)->private, false);
        return 0;
}

static const match_table_t qos_ctrl_tokens = {
        { QOS_ENABLE,           "enable=%u"     },
        { QOS_CTRL,             "ctrl=%s"       },
        { NR_QOS_CTRL_PARAMS,   NULL            },
};

static const match_table_t qos_tokens = {
        { QOS_RPPM,             "rpct=%s"       },
        { QOS_RLAT,             "rlat=%u"       },
        { QOS_WPPM,             "wpct=%s"       },
        { QOS_WLAT,             "wlat=%u"       },
        { QOS_MIN,              "min=%s"        },
        { QOS_MAX,              "max=%s"        },
        { NR_QOS_PARAMS,        NULL            },
};

static ssize_t ioc_qos_write(struct kernfs_open_file *of, char *input,
                             size_t nbytes, loff_t off)
{
        struct gendisk *disk;
        struct ioc *ioc;
        u32 qos[NR_QOS_PARAMS];
        bool enable, user;
        char *p;
        int ret;

        disk = blkcg_conf_get_disk(&input);
        if (IS_ERR(disk))
                return PTR_ERR(disk);

        ioc = q_to_ioc(disk->queue);
        if (!ioc) {
                ret = blk_iocost_init(disk->queue);
                if (ret)
                        goto err;
                ioc = q_to_ioc(disk->queue);
        }

        spin_lock_irq(&ioc->lock);
        memcpy(qos, ioc->params.qos, sizeof(qos));
        enable = ioc->enabled;
        user = ioc->user_qos_params;
        spin_unlock_irq(&ioc->lock);

        while ((p = strsep(&input, " \t\n"))) {
                substring_t args[MAX_OPT_ARGS];
                char buf[32];
                int tok;
                s64 v;

                if (!*p)
                        continue;

                switch (match_token(p, qos_ctrl_tokens, args)) {
                case QOS_ENABLE:
                        match_u64(&args[0], &v);
                        enable = v;
                        continue;
                case QOS_CTRL:
                        match_strlcpy(buf, &args[0], sizeof(buf));
                        if (!strcmp(buf, "auto"))
                                user = false;
                        else if (!strcmp(buf, "user"))
                                user = true;
                        else
                                goto einval;
                        continue;
                }

                tok = match_token(p, qos_tokens, args);
                switch (tok) {
                case QOS_RPPM:
                case QOS_WPPM:
                        if (match_strlcpy(buf, &args[0], sizeof(buf)) >=
                            sizeof(buf))
                                goto einval;
                        if (cgroup_parse_float(buf, 2, &v))
                                goto einval;
                        if (v < 0 || v > 10000)
                                goto einval;
                        qos[tok] = v * 100;
                        break;
                case QOS_RLAT:
                case QOS_WLAT:
                        if (match_u64(&args[0], &v))
                                goto einval;
                        qos[tok] = v;
                        break;
                case QOS_MIN:
                case QOS_MAX:
                        if (match_strlcpy(buf, &args[0], sizeof(buf)) >=
                            sizeof(buf))
                                goto einval;
                        if (cgroup_parse_float(buf, 2, &v))
                                goto einval;
                        if (v < 0)
                                goto einval;
                        qos[tok] = clamp_t(s64, v * 100,
                                           VRATE_MIN_PPM, VRATE_MAX_PPM);
                        break;
                default:
                        goto einval;
                }
                user = true;
        }

        if (qos[QOS_MIN] > qos[QOS_MAX])
                goto einval;

        spin_lock_irq(&ioc->lock);

        if (enable) {
                blk_stat_enable_accounting(ioc->rqos.q);
                blk_queue_flag_set(QUEUE_FLAG_RQ_ALLOC_TIME, ioc->rqos.q);
                ioc->enabled = true;
        } else {
                blk_queue_flag_clear(QUEUE_FLAG_RQ_ALLOC_TIME, ioc->rqos.q);
                ioc->enabled = false;
        }

        if (user) {
                memcpy(ioc->params.qos, qos, sizeof(qos));
                ioc->user_qos_params = true;
        } else {
                ioc->user_qos_params = false;
        }

        ioc_refresh_params(ioc, true);
        spin_unlock_irq(&ioc->lock);

        put_disk_and_module(disk);
        return nbytes;
einval:
        ret = -EINVAL;
err:
        put_disk_and_module(disk);
        return ret;
}

static u64 ioc_cost_model_prfill(struct seq_file *sf,
                                 struct blkg_policy_data *pd, int off)
{
        const char *dname = blkg_dev_name(pd->blkg);
        struct ioc *ioc = pd_to_iocg(pd)->ioc;
        u64 *u = ioc->params.i_lcoefs;

        if (!dname)
                return 0;

        seq_printf(sf, "%s ctrl=%s model=linear "
                   "rbps=%llu rseqiops=%llu rrandiops=%llu "
                   "wbps=%llu wseqiops=%llu wrandiops=%llu\n",
                   dname, ioc->user_cost_model ? "user" : "auto",
                   u[I_LCOEF_RBPS], u[I_LCOEF_RSEQIOPS], u[I_LCOEF_RRANDIOPS],
                   u[I_LCOEF_WBPS], u[I_LCOEF_WSEQIOPS], u[I_LCOEF_WRANDIOPS]);
        return 0;
}

static int ioc_cost_model_show(struct seq_file *sf, void *v)
{
        struct blkcg *blkcg = css_to_blkcg(seq_css(sf));

        blkcg_print_blkgs(sf, blkcg, ioc_cost_model_prfill,
                          &blkcg_policy_iocost, seq_cft(sf)->private, false);
        return 0;
}

static const match_table_t cost_ctrl_tokens = {
        { COST_CTRL,            "ctrl=%s"       },
        { COST_MODEL,           "model=%s"      },
        { NR_COST_CTRL_PARAMS,  NULL            },
};

static const match_table_t i_lcoef_tokens = {
        { I_LCOEF_RBPS,         "rbps=%u"       },
        { I_LCOEF_RSEQIOPS,     "rseqiops=%u"   },
        { I_LCOEF_RRANDIOPS,    "rrandiops=%u"  },
        { I_LCOEF_WBPS,         "wbps=%u"       },
        { I_LCOEF_WSEQIOPS,     "wseqiops=%u"   },
        { I_LCOEF_WRANDIOPS,    "wrandiops=%u"  },
        { NR_I_LCOEFS,          NULL            },
};

static ssize_t ioc_cost_model_write(struct kernfs_open_file *of, char *input,
                                    size_t nbytes, loff_t off)
{
        struct gendisk *disk;
        struct ioc *ioc;
        u64 u[NR_I_LCOEFS];
        bool user;
        char *p;
        int ret;

        disk = blkcg_conf_get_disk(&input);
        if (IS_ERR(disk))
                return PTR_ERR(disk);

        ioc = q_to_ioc(disk->queue);
        if (!ioc) {
                ret = blk_iocost_init(disk->queue);
                if (ret)
                        goto err;
                ioc = q_to_ioc(disk->queue);
        }

        spin_lock_irq(&ioc->lock);
        memcpy(u, ioc->params.i_lcoefs, sizeof(u));
        user = ioc->user_cost_model;
        spin_unlock_irq(&ioc->lock);

        while ((p = strsep(&input, " \t\n"))) {
                substring_t args[MAX_OPT_ARGS];
                char buf[32];
                int tok;
                u64 v;

                if (!*p)
                        continue;

                switch (match_token(p, cost_ctrl_tokens, args)) {
                case COST_CTRL:
                        match_strlcpy(buf, &args[0], sizeof(buf));
                        if (!strcmp(buf, "auto"))
                                user = false;
                        else if (!strcmp(buf, "user"))
                                user = true;
                        else
                                goto einval;
                        continue;
                case COST_MODEL:
                        match_strlcpy(buf, &args[0], sizeof(buf));
                        if (strcmp(buf, "linear"))
                                goto einval;
                        continue;
                }

                tok = match_token(p, i_lcoef_tokens, args);
                if (tok == NR_I_LCOEFS)
                        goto einval;
                if (match_u64(&args[0], &v))
                        goto einval;
                u[tok] = v;
                user = true;
        }

        spin_lock_irq(&ioc->lock);
        if (user) {
                memcpy(ioc->params.i_lcoefs, u, sizeof(u));
                ioc->user_cost_model = true;
        } else {
                ioc->user_cost_model = false;
        }
        ioc_refresh_params(ioc, true);
        spin_unlock_irq(&ioc->lock);

        put_disk_and_module(disk);
        return nbytes;

einval:
        ret = -EINVAL;
err:
        put_disk_and_module(disk);
        return ret;
}

static struct cftype ioc_files[] = {
        {
                .name = "weight",
                .flags = CFTYPE_NOT_ON_ROOT,
                .seq_show = ioc_weight_show,
                .write = ioc_weight_write,
        },
        {
                .name = "cost.qos",
                .flags = CFTYPE_ONLY_ON_ROOT,
                .seq_show = ioc_qos_show,
                .write = ioc_qos_write,
        },
        {
                .name = "cost.model",
                .flags = CFTYPE_ONLY_ON_ROOT,
                .seq_show = ioc_cost_model_show,
                .write = ioc_cost_model_write,
        },
        {}
};

static struct blkcg_policy blkcg_policy_iocost = {
        .dfl_cftypes    = ioc_files,
        .cpd_alloc_fn   = ioc_cpd_alloc,
        .cpd_free_fn    = ioc_cpd_free,
        .pd_alloc_fn    = ioc_pd_alloc,
        .pd_init_fn     = ioc_pd_init,
        .pd_free_fn     = ioc_pd_free,
};

static int __init ioc_init(void)
{
        return blkcg_policy_register(&blkcg_policy_iocost);
}

static void __exit ioc_exit(void)
{
        return blkcg_policy_unregister(&blkcg_policy_iocost);
}

module_init(ioc_init);
module_exit(ioc_exit);