[PATCH] 02/05: update ioscheds to use generic dispatch queue

[mirror_ubuntu-artful-kernel.git] / drivers / block / cfq-iosched.c

/*
 *  linux/drivers/block/cfq-iosched.c
 *
 *  CFQ, or complete fairness queueing, disk scheduler.
 *
 *  Based on ideas from a previously unfinished io
 *  scheduler (round robin per-process disk scheduling) and Andrea Arcangeli.
 *
 *  Copyright (C) 2003 Jens Axboe <axboe@suse.de>
 */
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/elevator.h>
#include <linux/bio.h>
#include <linux/config.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/compiler.h>
#include <linux/hash.h>
#include <linux/rbtree.h>
#include <linux/mempool.h>
#include <linux/ioprio.h>
#include <linux/writeback.h>

/*
 * tunables
 */
static int cfq_quantum = 4;             /* max queue in one round of service */
static int cfq_queued = 8;              /* minimum rq allocate limit per-queue*/
static int cfq_fifo_expire[2] = { HZ / 4, HZ / 8 };
static int cfq_back_max = 16 * 1024;    /* maximum backwards seek, in KiB */
static int cfq_back_penalty = 2;        /* penalty of a backwards seek */

static int cfq_slice_sync = HZ / 10;
static int cfq_slice_async = HZ / 25;
static int cfq_slice_async_rq = 2;
static int cfq_slice_idle = HZ / 100;

#define CFQ_IDLE_GRACE          (HZ / 10)
#define CFQ_SLICE_SCALE         (5)

#define CFQ_KEY_ASYNC           (0)
#define CFQ_KEY_ANY             (0xffff)

/*
 * disable queueing at the driver/hardware level
 */
static int cfq_max_depth = 2;

/*
 * for the hash of cfqq inside the cfqd
 */
#define CFQ_QHASH_SHIFT         6
#define CFQ_QHASH_ENTRIES       (1 << CFQ_QHASH_SHIFT)
#define list_entry_qhash(entry) hlist_entry((entry), struct cfq_queue, cfq_hash)

/*
 * for the hash of crq inside the cfqq
 */
#define CFQ_MHASH_SHIFT         6
#define CFQ_MHASH_BLOCK(sec)    ((sec) >> 3)
#define CFQ_MHASH_ENTRIES       (1 << CFQ_MHASH_SHIFT)
#define CFQ_MHASH_FN(sec)       hash_long(CFQ_MHASH_BLOCK(sec), CFQ_MHASH_SHIFT)
#define rq_hash_key(rq)         ((rq)->sector + (rq)->nr_sectors)
#define list_entry_hash(ptr)    hlist_entry((ptr), struct cfq_rq, hash)

#define list_entry_cfqq(ptr)    list_entry((ptr), struct cfq_queue, cfq_list)
#define list_entry_fifo(ptr)    list_entry((ptr), struct request, queuelist)

#define RQ_DATA(rq)             (rq)->elevator_private

/*
 * rb-tree defines
 */
#define RB_NONE                 (2)
#define RB_EMPTY(node)          ((node)->rb_node == NULL)
#define RB_CLEAR_COLOR(node)    (node)->rb_color = RB_NONE
#define RB_CLEAR(node)          do {    \
        (node)->rb_parent = NULL;       \
        RB_CLEAR_COLOR((node));         \
        (node)->rb_right = NULL;        \
        (node)->rb_left = NULL;         \
} while (0)
#define RB_CLEAR_ROOT(root)     ((root)->rb_node = NULL)
#define rb_entry_crq(node)      rb_entry((node), struct cfq_rq, rb_node)
#define rq_rb_key(rq)           (rq)->sector

static kmem_cache_t *crq_pool;
static kmem_cache_t *cfq_pool;
static kmem_cache_t *cfq_ioc_pool;

#define CFQ_PRIO_LISTS          IOPRIO_BE_NR
#define cfq_class_idle(cfqq)    ((cfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
#define cfq_class_be(cfqq)      ((cfqq)->ioprio_class == IOPRIO_CLASS_BE)
#define cfq_class_rt(cfqq)      ((cfqq)->ioprio_class == IOPRIO_CLASS_RT)

#define ASYNC                   (0)
#define SYNC                    (1)

#define cfq_cfqq_dispatched(cfqq)       \
        ((cfqq)->on_dispatch[ASYNC] + (cfqq)->on_dispatch[SYNC])

#define cfq_cfqq_class_sync(cfqq)       ((cfqq)->key != CFQ_KEY_ASYNC)

#define cfq_cfqq_sync(cfqq)             \
        (cfq_cfqq_class_sync(cfqq) || (cfqq)->on_dispatch[SYNC])

/*
 * Per block device queue structure
 */
struct cfq_data {
        atomic_t ref;
        request_queue_t *queue;

        /*
         * rr list of queues with requests and the count of them
         */
        struct list_head rr_list[CFQ_PRIO_LISTS];
        struct list_head busy_rr;
        struct list_head cur_rr;
        struct list_head idle_rr;
        unsigned int busy_queues;

        /*
         * non-ordered list of empty cfqq's
         */
        struct list_head empty_list;

        /*
         * cfqq lookup hash
         */
        struct hlist_head *cfq_hash;

        /*
         * global crq hash for all queues
         */
        struct hlist_head *crq_hash;

        unsigned int max_queued;

        mempool_t *crq_pool;

        int rq_in_driver;

        /*
         * schedule slice state info
         */
        /*
         * idle window management
         */
        struct timer_list idle_slice_timer;
        struct work_struct unplug_work;

        struct cfq_queue *active_queue;
        struct cfq_io_context *active_cic;
        int cur_prio, cur_end_prio;
        unsigned int dispatch_slice;

        struct timer_list idle_class_timer;

        sector_t last_sector;
        unsigned long last_end_request;

        unsigned int rq_starved;

        /*
         * tunables, see top of file
         */
        unsigned int cfq_quantum;
        unsigned int cfq_queued;
        unsigned int cfq_fifo_expire[2];
        unsigned int cfq_back_penalty;
        unsigned int cfq_back_max;
        unsigned int cfq_slice[2];
        unsigned int cfq_slice_async_rq;
        unsigned int cfq_slice_idle;
        unsigned int cfq_max_depth;
};

/*
 * Per process-grouping structure
 */
struct cfq_queue {
        /* reference count */
        atomic_t ref;
        /* parent cfq_data */
        struct cfq_data *cfqd;
        /* cfqq lookup hash */
        struct hlist_node cfq_hash;
        /* hash key */
        unsigned int key;
        /* on either rr or empty list of cfqd */
        struct list_head cfq_list;
        /* sorted list of pending requests */
        struct rb_root sort_list;
        /* if fifo isn't expired, next request to serve */
        struct cfq_rq *next_crq;
        /* requests queued in sort_list */
        int queued[2];
        /* currently allocated requests */
        int allocated[2];
        /* fifo list of requests in sort_list */
        struct list_head fifo;

        unsigned long slice_start;
        unsigned long slice_end;
        unsigned long slice_left;
        unsigned long service_last;

        /* number of requests that are on the dispatch list */
        int on_dispatch[2];

        /* io prio of this group */
        unsigned short ioprio, org_ioprio;
        unsigned short ioprio_class, org_ioprio_class;

        /* various state flags, see below */
        unsigned int flags;
};

struct cfq_rq {
        struct rb_node rb_node;
        sector_t rb_key;
        struct request *request;
        struct hlist_node hash;

        struct cfq_queue *cfq_queue;
        struct cfq_io_context *io_context;

        unsigned int crq_flags;
};

enum cfqq_state_flags {
        CFQ_CFQQ_FLAG_on_rr = 0,
        CFQ_CFQQ_FLAG_wait_request,
        CFQ_CFQQ_FLAG_must_alloc,
        CFQ_CFQQ_FLAG_must_alloc_slice,
        CFQ_CFQQ_FLAG_must_dispatch,
        CFQ_CFQQ_FLAG_fifo_expire,
        CFQ_CFQQ_FLAG_idle_window,
        CFQ_CFQQ_FLAG_prio_changed,
        CFQ_CFQQ_FLAG_expired,
};

#define CFQ_CFQQ_FNS(name)                                              \
static inline void cfq_mark_cfqq_##name(struct cfq_queue *cfqq)         \
{                                                                       \
        cfqq->flags |= (1 << CFQ_CFQQ_FLAG_##name);                     \
}                                                                       \
static inline void cfq_clear_cfqq_##name(struct cfq_queue *cfqq)        \
{                                                                       \
        cfqq->flags &= ~(1 << CFQ_CFQQ_FLAG_##name);                    \
}                                                                       \
static inline int cfq_cfqq_##name(const struct cfq_queue *cfqq)         \
{                                                                       \
        return (cfqq->flags & (1 << CFQ_CFQQ_FLAG_##name)) != 0;        \
}

CFQ_CFQQ_FNS(on_rr);
CFQ_CFQQ_FNS(wait_request);
CFQ_CFQQ_FNS(must_alloc);
CFQ_CFQQ_FNS(must_alloc_slice);
CFQ_CFQQ_FNS(must_dispatch);
CFQ_CFQQ_FNS(fifo_expire);
CFQ_CFQQ_FNS(idle_window);
CFQ_CFQQ_FNS(prio_changed);
CFQ_CFQQ_FNS(expired);
#undef CFQ_CFQQ_FNS

enum cfq_rq_state_flags {
        CFQ_CRQ_FLAG_is_sync = 0,
};

#define CFQ_CRQ_FNS(name)                                               \
static inline void cfq_mark_crq_##name(struct cfq_rq *crq)              \
{                                                                       \
        crq->crq_flags |= (1 << CFQ_CRQ_FLAG_##name);                   \
}                                                                       \
static inline void cfq_clear_crq_##name(struct cfq_rq *crq)             \
{                                                                       \
        crq->crq_flags &= ~(1 << CFQ_CRQ_FLAG_##name);                  \
}                                                                       \
static inline int cfq_crq_##name(const struct cfq_rq *crq)              \
{                                                                       \
        return (crq->crq_flags & (1 << CFQ_CRQ_FLAG_##name)) != 0;      \
}

CFQ_CRQ_FNS(is_sync);
#undef CFQ_CRQ_FNS

static struct cfq_queue *cfq_find_cfq_hash(struct cfq_data *, unsigned int, unsigned short);
static void cfq_dispatch_insert(request_queue_t *, struct cfq_rq *);
static void cfq_put_cfqd(struct cfq_data *cfqd);

#define process_sync(tsk)       ((tsk)->flags & PF_SYNCWRITE)

/*
 * lots of deadline iosched dupes, can be abstracted later...
 */
static inline void cfq_del_crq_hash(struct cfq_rq *crq)
{
        hlist_del_init(&crq->hash);
}

static void cfq_remove_merge_hints(request_queue_t *q, struct cfq_rq *crq)
{
        cfq_del_crq_hash(crq);

        if (q->last_merge == crq->request)
                q->last_merge = NULL;
}

static inline void cfq_add_crq_hash(struct cfq_data *cfqd, struct cfq_rq *crq)
{
        const int hash_idx = CFQ_MHASH_FN(rq_hash_key(crq->request));

        hlist_add_head(&crq->hash, &cfqd->crq_hash[hash_idx]);
}

static struct request *cfq_find_rq_hash(struct cfq_data *cfqd, sector_t offset)
{
        struct hlist_head *hash_list = &cfqd->crq_hash[CFQ_MHASH_FN(offset)];
        struct hlist_node *entry, *next;

        hlist_for_each_safe(entry, next, hash_list) {
                struct cfq_rq *crq = list_entry_hash(entry);
                struct request *__rq = crq->request;

                if (!rq_mergeable(__rq)) {
                        cfq_del_crq_hash(crq);
                        continue;
                }

                if (rq_hash_key(__rq) == offset)
                        return __rq;
        }

        return NULL;
}

/*
 * scheduler run of queue, if there are requests pending and no one in the
 * driver that will restart queueing
 */
static inline void cfq_schedule_dispatch(struct cfq_data *cfqd)
{
        if (!cfqd->rq_in_driver && cfqd->busy_queues)
                kblockd_schedule_work(&cfqd->unplug_work);
}

static int cfq_queue_empty(request_queue_t *q)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;

        return !cfqd->busy_queues;
}

/*
 * Lifted from AS - choose which of crq1 and crq2 that is best served now.
 * We choose the request that is closest to the head right now. Distance
 * behind the head are penalized and only allowed to a certain extent.
 */
static struct cfq_rq *
cfq_choose_req(struct cfq_data *cfqd, struct cfq_rq *crq1, struct cfq_rq *crq2)
{
        sector_t last, s1, s2, d1 = 0, d2 = 0;
        int r1_wrap = 0, r2_wrap = 0;   /* requests are behind the disk head */
        unsigned long back_max;

        if (crq1 == NULL || crq1 == crq2)
                return crq2;
        if (crq2 == NULL)
                return crq1;

        if (cfq_crq_is_sync(crq1) && !cfq_crq_is_sync(crq2))
                return crq1;
        else if (cfq_crq_is_sync(crq2) && !cfq_crq_is_sync(crq1))
                return crq2;

        s1 = crq1->request->sector;
        s2 = crq2->request->sector;

        last = cfqd->last_sector;

        /*
         * by definition, 1KiB is 2 sectors
         */
        back_max = cfqd->cfq_back_max * 2;

        /*
         * Strict one way elevator _except_ in the case where we allow
         * short backward seeks which are biased as twice the cost of a
         * similar forward seek.
         */
        if (s1 >= last)
                d1 = s1 - last;
        else if (s1 + back_max >= last)
                d1 = (last - s1) * cfqd->cfq_back_penalty;
        else
                r1_wrap = 1;

        if (s2 >= last)
                d2 = s2 - last;
        else if (s2 + back_max >= last)
                d2 = (last - s2) * cfqd->cfq_back_penalty;
        else
                r2_wrap = 1;

        /* Found required data */
        if (!r1_wrap && r2_wrap)
                return crq1;
        else if (!r2_wrap && r1_wrap)
                return crq2;
        else if (r1_wrap && r2_wrap) {
                /* both behind the head */
                if (s1 <= s2)
                        return crq1;
                else
                        return crq2;
        }

        /* Both requests in front of the head */
        if (d1 < d2)
                return crq1;
        else if (d2 < d1)
                return crq2;
        else {
                if (s1 >= s2)
                        return crq1;
                else
                        return crq2;
        }
}

/*
 * would be nice to take fifo expire time into account as well
 */
static struct cfq_rq *
cfq_find_next_crq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                  struct cfq_rq *last)
{
        struct cfq_rq *crq_next = NULL, *crq_prev = NULL;
        struct rb_node *rbnext, *rbprev;

        if (!(rbnext = rb_next(&last->rb_node))) {
                rbnext = rb_first(&cfqq->sort_list);
                if (rbnext == &last->rb_node)
                        rbnext = NULL;
        }

        rbprev = rb_prev(&last->rb_node);

        if (rbprev)
                crq_prev = rb_entry_crq(rbprev);
        if (rbnext)
                crq_next = rb_entry_crq(rbnext);

        return cfq_choose_req(cfqd, crq_next, crq_prev);
}

static void cfq_update_next_crq(struct cfq_rq *crq)
{
        struct cfq_queue *cfqq = crq->cfq_queue;

        if (cfqq->next_crq == crq)
                cfqq->next_crq = cfq_find_next_crq(cfqq->cfqd, cfqq, crq);
}

static void cfq_resort_rr_list(struct cfq_queue *cfqq, int preempted)
{
        struct cfq_data *cfqd = cfqq->cfqd;
        struct list_head *list, *entry;

        BUG_ON(!cfq_cfqq_on_rr(cfqq));

        list_del(&cfqq->cfq_list);

        if (cfq_class_rt(cfqq))
                list = &cfqd->cur_rr;
        else if (cfq_class_idle(cfqq))
                list = &cfqd->idle_rr;
        else {
                /*
                 * if cfqq has requests in flight, don't allow it to be
                 * found in cfq_set_active_queue before it has finished them.
                 * this is done to increase fairness between a process that
                 * has lots of io pending vs one that only generates one
                 * sporadically or synchronously
                 */
                if (cfq_cfqq_dispatched(cfqq))
                        list = &cfqd->busy_rr;
                else
                        list = &cfqd->rr_list[cfqq->ioprio];
        }

        /*
         * if queue was preempted, just add to front to be fair. busy_rr
         * isn't sorted.
         */
        if (preempted || list == &cfqd->busy_rr) {
                list_add(&cfqq->cfq_list, list);
                return;
        }

        /*
         * sort by when queue was last serviced
         */
        entry = list;
        while ((entry = entry->prev) != list) {
                struct cfq_queue *__cfqq = list_entry_cfqq(entry);

                if (!__cfqq->service_last)
                        break;
                if (time_before(__cfqq->service_last, cfqq->service_last))
                        break;
        }

        list_add(&cfqq->cfq_list, entry);
}

/*
 * add to busy list of queues for service, trying to be fair in ordering
 * the pending list according to last request service
 */
static inline void
cfq_add_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        BUG_ON(cfq_cfqq_on_rr(cfqq));
        cfq_mark_cfqq_on_rr(cfqq);
        cfqd->busy_queues++;

        cfq_resort_rr_list(cfqq, 0);
}

static inline void
cfq_del_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        BUG_ON(!cfq_cfqq_on_rr(cfqq));
        cfq_clear_cfqq_on_rr(cfqq);
        list_move(&cfqq->cfq_list, &cfqd->empty_list);

        BUG_ON(!cfqd->busy_queues);
        cfqd->busy_queues--;
}

/*
 * rb tree support functions
 */
static inline void cfq_del_crq_rb(struct cfq_rq *crq)
{
        struct cfq_queue *cfqq = crq->cfq_queue;
        struct cfq_data *cfqd = cfqq->cfqd;
        const int sync = cfq_crq_is_sync(crq);

        BUG_ON(!cfqq->queued[sync]);
        cfqq->queued[sync]--;

        cfq_update_next_crq(crq);

        rb_erase(&crq->rb_node, &cfqq->sort_list);
        RB_CLEAR_COLOR(&crq->rb_node);

        if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY(&cfqq->sort_list))
                cfq_del_cfqq_rr(cfqd, cfqq);
}

static struct cfq_rq *
__cfq_add_crq_rb(struct cfq_rq *crq)
{
        struct rb_node **p = &crq->cfq_queue->sort_list.rb_node;
        struct rb_node *parent = NULL;
        struct cfq_rq *__crq;

        while (*p) {
                parent = *p;
                __crq = rb_entry_crq(parent);

                if (crq->rb_key < __crq->rb_key)
                        p = &(*p)->rb_left;
                else if (crq->rb_key > __crq->rb_key)
                        p = &(*p)->rb_right;
                else
                        return __crq;
        }

        rb_link_node(&crq->rb_node, parent, p);
        return NULL;
}

static void cfq_add_crq_rb(struct cfq_rq *crq)
{
        struct cfq_queue *cfqq = crq->cfq_queue;
        struct cfq_data *cfqd = cfqq->cfqd;
        struct request *rq = crq->request;
        struct cfq_rq *__alias;

        crq->rb_key = rq_rb_key(rq);
        cfqq->queued[cfq_crq_is_sync(crq)]++;

        /*
         * looks a little odd, but the first insert might return an alias.
         * if that happens, put the alias on the dispatch list
         */
        while ((__alias = __cfq_add_crq_rb(crq)) != NULL)
                cfq_dispatch_insert(cfqd->queue, __alias);

        rb_insert_color(&crq->rb_node, &cfqq->sort_list);

        if (!cfq_cfqq_on_rr(cfqq))
                cfq_add_cfqq_rr(cfqd, cfqq);

        /*
         * check if this request is a better next-serve candidate
         */
        cfqq->next_crq = cfq_choose_req(cfqd, cfqq->next_crq, crq);
}

static inline void
cfq_reposition_crq_rb(struct cfq_queue *cfqq, struct cfq_rq *crq)
{
        rb_erase(&crq->rb_node, &cfqq->sort_list);
        cfqq->queued[cfq_crq_is_sync(crq)]--;

        cfq_add_crq_rb(crq);
}

static struct request *cfq_find_rq_rb(struct cfq_data *cfqd, sector_t sector)

{
        struct cfq_queue *cfqq = cfq_find_cfq_hash(cfqd, current->pid, CFQ_KEY_ANY);
        struct rb_node *n;

        if (!cfqq)
                goto out;

        n = cfqq->sort_list.rb_node;
        while (n) {
                struct cfq_rq *crq = rb_entry_crq(n);

                if (sector < crq->rb_key)
                        n = n->rb_left;
                else if (sector > crq->rb_key)
                        n = n->rb_right;
                else
                        return crq->request;
        }

out:
        return NULL;
}

static void cfq_activate_request(request_queue_t *q, struct request *rq)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;

        cfqd->rq_in_driver++;
}

static void cfq_deactivate_request(request_queue_t *q, struct request *rq)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;

        WARN_ON(!cfqd->rq_in_driver);
        cfqd->rq_in_driver--;
}

static void cfq_remove_request(struct request *rq)
{
        struct cfq_rq *crq = RQ_DATA(rq);

        list_del_init(&rq->queuelist);
        cfq_del_crq_rb(crq);
        cfq_remove_merge_hints(rq->q, crq);
}

static int
cfq_merge(request_queue_t *q, struct request **req, struct bio *bio)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct request *__rq;
        int ret;

        ret = elv_try_last_merge(q, bio);
        if (ret != ELEVATOR_NO_MERGE) {
                __rq = q->last_merge;
                goto out_insert;
        }

        __rq = cfq_find_rq_hash(cfqd, bio->bi_sector);
        if (__rq && elv_rq_merge_ok(__rq, bio)) {
                ret = ELEVATOR_BACK_MERGE;
                goto out;
        }

        __rq = cfq_find_rq_rb(cfqd, bio->bi_sector + bio_sectors(bio));
        if (__rq && elv_rq_merge_ok(__rq, bio)) {
                ret = ELEVATOR_FRONT_MERGE;
                goto out;
        }

        return ELEVATOR_NO_MERGE;
out:
        q->last_merge = __rq;
out_insert:
        *req = __rq;
        return ret;
}

static void cfq_merged_request(request_queue_t *q, struct request *req)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct cfq_rq *crq = RQ_DATA(req);

        cfq_del_crq_hash(crq);
        cfq_add_crq_hash(cfqd, crq);

        if (rq_rb_key(req) != crq->rb_key) {
                struct cfq_queue *cfqq = crq->cfq_queue;

                cfq_update_next_crq(crq);
                cfq_reposition_crq_rb(cfqq, crq);
        }

        q->last_merge = req;
}

static void
cfq_merged_requests(request_queue_t *q, struct request *rq,
                    struct request *next)
{
        cfq_merged_request(q, rq);

        /*
         * reposition in fifo if next is older than rq
         */
        if (!list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
            time_before(next->start_time, rq->start_time))
                list_move(&rq->queuelist, &next->queuelist);

        cfq_remove_request(next);
}

static inline void
__cfq_set_active_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        if (cfqq) {
                /*
                 * stop potential idle class queues waiting service
                 */
                del_timer(&cfqd->idle_class_timer);

                cfqq->slice_start = jiffies;
                cfqq->slice_end = 0;
                cfqq->slice_left = 0;
                cfq_clear_cfqq_must_alloc_slice(cfqq);
                cfq_clear_cfqq_fifo_expire(cfqq);
                cfq_clear_cfqq_expired(cfqq);
        }

        cfqd->active_queue = cfqq;
}

/*
 * 0
 * 0,1
 * 0,1,2
 * 0,1,2,3
 * 0,1,2,3,4
 * 0,1,2,3,4,5
 * 0,1,2,3,4,5,6
 * 0,1,2,3,4,5,6,7
 */
static int cfq_get_next_prio_level(struct cfq_data *cfqd)
{
        int prio, wrap;

        prio = -1;
        wrap = 0;
        do {
                int p;

                for (p = cfqd->cur_prio; p <= cfqd->cur_end_prio; p++) {
                        if (!list_empty(&cfqd->rr_list[p])) {
                                prio = p;
                                break;
                        }
                }

                if (prio != -1)
                        break;
                cfqd->cur_prio = 0;
                if (++cfqd->cur_end_prio == CFQ_PRIO_LISTS) {
                        cfqd->cur_end_prio = 0;
                        if (wrap)
                                break;
                        wrap = 1;
                }
        } while (1);

        if (unlikely(prio == -1))
                return -1;

        BUG_ON(prio >= CFQ_PRIO_LISTS);

        list_splice_init(&cfqd->rr_list[prio], &cfqd->cur_rr);

        cfqd->cur_prio = prio + 1;
        if (cfqd->cur_prio > cfqd->cur_end_prio) {
                cfqd->cur_end_prio = cfqd->cur_prio;
                cfqd->cur_prio = 0;
        }
        if (cfqd->cur_end_prio == CFQ_PRIO_LISTS) {
                cfqd->cur_prio = 0;
                cfqd->cur_end_prio = 0;
        }

        return prio;
}

static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd)
{
        struct cfq_queue *cfqq;

        /*
         * if current queue is expired but not done with its requests yet,
         * wait for that to happen
         */
        if ((cfqq = cfqd->active_queue) != NULL) {
                if (cfq_cfqq_expired(cfqq) && cfq_cfqq_dispatched(cfqq))
                        return NULL;
        }

        /*
         * if current list is non-empty, grab first entry. if it is empty,
         * get next prio level and grab first entry then if any are spliced
         */
        if (!list_empty(&cfqd->cur_rr) || cfq_get_next_prio_level(cfqd) != -1)
                cfqq = list_entry_cfqq(cfqd->cur_rr.next);

        /*
         * if we have idle queues and no rt or be queues had pending
         * requests, either allow immediate service if the grace period
         * has passed or arm the idle grace timer
         */
        if (!cfqq && !list_empty(&cfqd->idle_rr)) {
                unsigned long end = cfqd->last_end_request + CFQ_IDLE_GRACE;

                if (time_after_eq(jiffies, end))
                        cfqq = list_entry_cfqq(cfqd->idle_rr.next);
                else
                        mod_timer(&cfqd->idle_class_timer, end);
        }

        __cfq_set_active_queue(cfqd, cfqq);
        return cfqq;
}

/*
 * current cfqq expired its slice (or was too idle), select new one
 */
static void
__cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                    int preempted)
{
        unsigned long now = jiffies;

        if (cfq_cfqq_wait_request(cfqq))
                del_timer(&cfqd->idle_slice_timer);

        if (!preempted && !cfq_cfqq_dispatched(cfqq))
                cfqq->service_last = now;

        cfq_clear_cfqq_must_dispatch(cfqq);
        cfq_clear_cfqq_wait_request(cfqq);

        /*
         * store what was left of this slice, if the queue idled out
         * or was preempted
         */
        if (time_after(now, cfqq->slice_end))
                cfqq->slice_left = now - cfqq->slice_end;
        else
                cfqq->slice_left = 0;

        if (cfq_cfqq_on_rr(cfqq))
                cfq_resort_rr_list(cfqq, preempted);

        if (cfqq == cfqd->active_queue)
                cfqd->active_queue = NULL;

        if (cfqd->active_cic) {
                put_io_context(cfqd->active_cic->ioc);
                cfqd->active_cic = NULL;
        }

        cfqd->dispatch_slice = 0;
}

static inline void cfq_slice_expired(struct cfq_data *cfqd, int preempted)
{
        struct cfq_queue *cfqq = cfqd->active_queue;

        if (cfqq) {
                /*
                 * use deferred expiry, if there are requests in progress as
                 * not to disturb the slice of the next queue
                 */
                if (cfq_cfqq_dispatched(cfqq))
                        cfq_mark_cfqq_expired(cfqq);
                else
                        __cfq_slice_expired(cfqd, cfqq, preempted);
        }
}

static int cfq_arm_slice_timer(struct cfq_data *cfqd, struct cfq_queue *cfqq)

{
        WARN_ON(!RB_EMPTY(&cfqq->sort_list));
        WARN_ON(cfqq != cfqd->active_queue);

        /*
         * idle is disabled, either manually or by past process history
         */
        if (!cfqd->cfq_slice_idle)
                return 0;
        if (!cfq_cfqq_idle_window(cfqq))
                return 0;
        /*
         * task has exited, don't wait
         */
        if (cfqd->active_cic && !cfqd->active_cic->ioc->task)
                return 0;

        cfq_mark_cfqq_must_dispatch(cfqq);
        cfq_mark_cfqq_wait_request(cfqq);

        if (!timer_pending(&cfqd->idle_slice_timer)) {
                unsigned long slice_left = min(cfqq->slice_end - 1, (unsigned long) cfqd->cfq_slice_idle);

                cfqd->idle_slice_timer.expires = jiffies + slice_left;
                add_timer(&cfqd->idle_slice_timer);
        }

        return 1;
}

static void cfq_dispatch_insert(request_queue_t *q, struct cfq_rq *crq)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct cfq_queue *cfqq = crq->cfq_queue;

        cfqq->next_crq = cfq_find_next_crq(cfqd, cfqq, crq);
        cfq_remove_request(crq->request);
        cfqq->on_dispatch[cfq_crq_is_sync(crq)]++;
        elv_dispatch_sort(q, crq->request);
}

/*
 * return expired entry, or NULL to just start from scratch in rbtree
 */
static inline struct cfq_rq *cfq_check_fifo(struct cfq_queue *cfqq)
{
        struct cfq_data *cfqd = cfqq->cfqd;
        struct request *rq;
        struct cfq_rq *crq;

        if (cfq_cfqq_fifo_expire(cfqq))
                return NULL;

        if (!list_empty(&cfqq->fifo)) {
                int fifo = cfq_cfqq_class_sync(cfqq);

                crq = RQ_DATA(list_entry_fifo(cfqq->fifo.next));
                rq = crq->request;
                if (time_after(jiffies, rq->start_time + cfqd->cfq_fifo_expire[fifo])) {
                        cfq_mark_cfqq_fifo_expire(cfqq);
                        return crq;
                }
        }

        return NULL;
}

/*
 * Scale schedule slice based on io priority. Use the sync time slice only
 * if a queue is marked sync and has sync io queued. A sync queue with async
 * io only, should not get full sync slice length.
 */
static inline int
cfq_prio_to_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        const int base_slice = cfqd->cfq_slice[cfq_cfqq_sync(cfqq)];

        WARN_ON(cfqq->ioprio >= IOPRIO_BE_NR);

        return base_slice + (base_slice/CFQ_SLICE_SCALE * (4 - cfqq->ioprio));
}

static inline void
cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        cfqq->slice_end = cfq_prio_to_slice(cfqd, cfqq) + jiffies;
}

static inline int
cfq_prio_to_maxrq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        const int base_rq = cfqd->cfq_slice_async_rq;

        WARN_ON(cfqq->ioprio >= IOPRIO_BE_NR);

        return 2 * (base_rq + base_rq * (CFQ_PRIO_LISTS - 1 - cfqq->ioprio));
}

/*
 * get next queue for service
 */
static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd, int force)
{
        unsigned long now = jiffies;
        struct cfq_queue *cfqq;

        cfqq = cfqd->active_queue;
        if (!cfqq)
                goto new_queue;

        if (cfq_cfqq_expired(cfqq))
                goto new_queue;

        /*
         * slice has expired
         */
        if (!cfq_cfqq_must_dispatch(cfqq) && time_after(now, cfqq->slice_end))
                goto expire;

        /*
         * if queue has requests, dispatch one. if not, check if
         * enough slice is left to wait for one
         */
        if (!RB_EMPTY(&cfqq->sort_list))
                goto keep_queue;
        else if (!force && cfq_cfqq_class_sync(cfqq) &&
                 time_before(now, cfqq->slice_end)) {
                if (cfq_arm_slice_timer(cfqd, cfqq))
                        return NULL;
        }

expire:
        cfq_slice_expired(cfqd, 0);
new_queue:
        cfqq = cfq_set_active_queue(cfqd);
keep_queue:
        return cfqq;
}

static int
__cfq_dispatch_requests(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                        int max_dispatch)
{
        int dispatched = 0;

        BUG_ON(RB_EMPTY(&cfqq->sort_list));

        do {
                struct cfq_rq *crq;

                /*
                 * follow expired path, else get first next available
                 */
                if ((crq = cfq_check_fifo(cfqq)) == NULL)
                        crq = cfqq->next_crq;

                /*
                 * finally, insert request into driver dispatch list
                 */
                cfq_dispatch_insert(cfqd->queue, crq);

                cfqd->dispatch_slice++;
                dispatched++;

                if (!cfqd->active_cic) {
                        atomic_inc(&crq->io_context->ioc->refcount);
                        cfqd->active_cic = crq->io_context;
                }

                if (RB_EMPTY(&cfqq->sort_list))
                        break;

        } while (dispatched < max_dispatch);

        /*
         * if slice end isn't set yet, set it. if at least one request was
         * sync, use the sync time slice value
         */
        if (!cfqq->slice_end)
                cfq_set_prio_slice(cfqd, cfqq);

        /*
         * expire an async queue immediately if it has used up its slice. idle
         * queue always expire after 1 dispatch round.
         */
        if ((!cfq_cfqq_sync(cfqq) &&
            cfqd->dispatch_slice >= cfq_prio_to_maxrq(cfqd, cfqq)) ||
            cfq_class_idle(cfqq))
                cfq_slice_expired(cfqd, 0);

        return dispatched;
}

static int
cfq_dispatch_requests(request_queue_t *q, int force)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct cfq_queue *cfqq;

        if (!cfqd->busy_queues)
                return 0;

        cfqq = cfq_select_queue(cfqd, force);
        if (cfqq) {
                int max_dispatch;

                /*
                 * if idle window is disabled, allow queue buildup
                 */
                if (!cfq_cfqq_idle_window(cfqq) &&
                    cfqd->rq_in_driver >= cfqd->cfq_max_depth)
                        return 0;

                cfq_clear_cfqq_must_dispatch(cfqq);
                cfq_clear_cfqq_wait_request(cfqq);
                del_timer(&cfqd->idle_slice_timer);

                if (!force) {
                        max_dispatch = cfqd->cfq_quantum;
                        if (cfq_class_idle(cfqq))
                                max_dispatch = 1;
                } else
                        max_dispatch = INT_MAX;

                return __cfq_dispatch_requests(cfqd, cfqq, max_dispatch);
        }

        return 0;
}

/*
 * task holds one reference to the queue, dropped when task exits. each crq
 * in-flight on this queue also holds a reference, dropped when crq is freed.
 *
 * queue lock must be held here.
 */
static void cfq_put_queue(struct cfq_queue *cfqq)
{
        struct cfq_data *cfqd = cfqq->cfqd;

        BUG_ON(atomic_read(&cfqq->ref) <= 0);

        if (!atomic_dec_and_test(&cfqq->ref))
                return;

        BUG_ON(rb_first(&cfqq->sort_list));
        BUG_ON(cfqq->allocated[READ] + cfqq->allocated[WRITE]);
        BUG_ON(cfq_cfqq_on_rr(cfqq));

        if (unlikely(cfqd->active_queue == cfqq)) {
                __cfq_slice_expired(cfqd, cfqq, 0);
                cfq_schedule_dispatch(cfqd);
        }

        cfq_put_cfqd(cfqq->cfqd);

        /*
         * it's on the empty list and still hashed
         */
        list_del(&cfqq->cfq_list);
        hlist_del(&cfqq->cfq_hash);
        kmem_cache_free(cfq_pool, cfqq);
}

static inline struct cfq_queue *
__cfq_find_cfq_hash(struct cfq_data *cfqd, unsigned int key, unsigned int prio,
                    const int hashval)
{
        struct hlist_head *hash_list = &cfqd->cfq_hash[hashval];
        struct hlist_node *entry, *next;

        hlist_for_each_safe(entry, next, hash_list) {
                struct cfq_queue *__cfqq = list_entry_qhash(entry);
                const unsigned short __p = IOPRIO_PRIO_VALUE(__cfqq->ioprio_class, __cfqq->ioprio);

                if (__cfqq->key == key && (__p == prio || prio == CFQ_KEY_ANY))
                        return __cfqq;
        }

        return NULL;
}

static struct cfq_queue *
cfq_find_cfq_hash(struct cfq_data *cfqd, unsigned int key, unsigned short prio)
{
        return __cfq_find_cfq_hash(cfqd, key, prio, hash_long(key, CFQ_QHASH_SHIFT));
}

static void cfq_free_io_context(struct cfq_io_context *cic)
{
        struct cfq_io_context *__cic;
        struct list_head *entry, *next;

        list_for_each_safe(entry, next, &cic->list) {
                __cic = list_entry(entry, struct cfq_io_context, list);
                kmem_cache_free(cfq_ioc_pool, __cic);
        }

        kmem_cache_free(cfq_ioc_pool, cic);
}

/*
 * Called with interrupts disabled
 */
static void cfq_exit_single_io_context(struct cfq_io_context *cic)
{
        struct cfq_data *cfqd = cic->cfqq->cfqd;
        request_queue_t *q = cfqd->queue;

        WARN_ON(!irqs_disabled());

        spin_lock(q->queue_lock);

        if (unlikely(cic->cfqq == cfqd->active_queue)) {
                __cfq_slice_expired(cfqd, cic->cfqq, 0);
                cfq_schedule_dispatch(cfqd);
        }

        cfq_put_queue(cic->cfqq);
        cic->cfqq = NULL;
        spin_unlock(q->queue_lock);
}

/*
 * Another task may update the task cic list, if it is doing a queue lookup
 * on its behalf. cfq_cic_lock excludes such concurrent updates
 */
static void cfq_exit_io_context(struct cfq_io_context *cic)
{
        struct cfq_io_context *__cic;
        struct list_head *entry;
        unsigned long flags;

        local_irq_save(flags);

        /*
         * put the reference this task is holding to the various queues
         */
        list_for_each(entry, &cic->list) {
                __cic = list_entry(entry, struct cfq_io_context, list);
                cfq_exit_single_io_context(__cic);
        }

        cfq_exit_single_io_context(cic);
        local_irq_restore(flags);
}

static struct cfq_io_context *
cfq_alloc_io_context(struct cfq_data *cfqd, int gfp_mask)
{
        struct cfq_io_context *cic = kmem_cache_alloc(cfq_ioc_pool, gfp_mask);

        if (cic) {
                INIT_LIST_HEAD(&cic->list);
                cic->cfqq = NULL;
                cic->key = NULL;
                cic->last_end_request = jiffies;
                cic->ttime_total = 0;
                cic->ttime_samples = 0;
                cic->ttime_mean = 0;
                cic->dtor = cfq_free_io_context;
                cic->exit = cfq_exit_io_context;
        }

        return cic;
}

static void cfq_init_prio_data(struct cfq_queue *cfqq)
{
        struct task_struct *tsk = current;
        int ioprio_class;

        if (!cfq_cfqq_prio_changed(cfqq))
                return;

        ioprio_class = IOPRIO_PRIO_CLASS(tsk->ioprio);
        switch (ioprio_class) {
                default:
                        printk(KERN_ERR "cfq: bad prio %x\n", ioprio_class);
                case IOPRIO_CLASS_NONE:
                        /*
                         * no prio set, place us in the middle of the BE classes
                         */
                        cfqq->ioprio = task_nice_ioprio(tsk);
                        cfqq->ioprio_class = IOPRIO_CLASS_BE;
                        break;
                case IOPRIO_CLASS_RT:
                        cfqq->ioprio = task_ioprio(tsk);
                        cfqq->ioprio_class = IOPRIO_CLASS_RT;
                        break;
                case IOPRIO_CLASS_BE:
                        cfqq->ioprio = task_ioprio(tsk);
                        cfqq->ioprio_class = IOPRIO_CLASS_BE;
                        break;
                case IOPRIO_CLASS_IDLE:
                        cfqq->ioprio_class = IOPRIO_CLASS_IDLE;
                        cfqq->ioprio = 7;
                        cfq_clear_cfqq_idle_window(cfqq);
                        break;
        }

        /*
         * keep track of original prio settings in case we have to temporarily
         * elevate the priority of this queue
         */
        cfqq->org_ioprio = cfqq->ioprio;
        cfqq->org_ioprio_class = cfqq->ioprio_class;

        if (cfq_cfqq_on_rr(cfqq))
                cfq_resort_rr_list(cfqq, 0);

        cfq_clear_cfqq_prio_changed(cfqq);
}

static inline void changed_ioprio(struct cfq_queue *cfqq)
{
        if (cfqq) {
                struct cfq_data *cfqd = cfqq->cfqd;

                spin_lock(cfqd->queue->queue_lock);
                cfq_mark_cfqq_prio_changed(cfqq);
                cfq_init_prio_data(cfqq);
                spin_unlock(cfqd->queue->queue_lock);
        }
}

/*
 * callback from sys_ioprio_set, irqs are disabled
 */
static int cfq_ioc_set_ioprio(struct io_context *ioc, unsigned int ioprio)
{
        struct cfq_io_context *cic = ioc->cic;

        changed_ioprio(cic->cfqq);

        list_for_each_entry(cic, &cic->list, list)
                changed_ioprio(cic->cfqq);

        return 0;
}

static struct cfq_queue *
cfq_get_queue(struct cfq_data *cfqd, unsigned int key, unsigned short ioprio,
              int gfp_mask)
{
        const int hashval = hash_long(key, CFQ_QHASH_SHIFT);
        struct cfq_queue *cfqq, *new_cfqq = NULL;

retry:
        cfqq = __cfq_find_cfq_hash(cfqd, key, ioprio, hashval);

        if (!cfqq) {
                if (new_cfqq) {
                        cfqq = new_cfqq;
                        new_cfqq = NULL;
                } else if (gfp_mask & __GFP_WAIT) {
                        spin_unlock_irq(cfqd->queue->queue_lock);
                        new_cfqq = kmem_cache_alloc(cfq_pool, gfp_mask);
                        spin_lock_irq(cfqd->queue->queue_lock);
                        goto retry;
                } else {
                        cfqq = kmem_cache_alloc(cfq_pool, gfp_mask);
                        if (!cfqq)
                                goto out;
                }

                memset(cfqq, 0, sizeof(*cfqq));

                INIT_HLIST_NODE(&cfqq->cfq_hash);
                INIT_LIST_HEAD(&cfqq->cfq_list);
                RB_CLEAR_ROOT(&cfqq->sort_list);
                INIT_LIST_HEAD(&cfqq->fifo);

                cfqq->key = key;
                hlist_add_head(&cfqq->cfq_hash, &cfqd->cfq_hash[hashval]);
                atomic_set(&cfqq->ref, 0);
                cfqq->cfqd = cfqd;
                atomic_inc(&cfqd->ref);
                cfqq->service_last = 0;
                /*
                 * set ->slice_left to allow preemption for a new process
                 */
                cfqq->slice_left = 2 * cfqd->cfq_slice_idle;
                cfq_mark_cfqq_idle_window(cfqq);
                cfq_mark_cfqq_prio_changed(cfqq);
                cfq_init_prio_data(cfqq);
        }

        if (new_cfqq)
                kmem_cache_free(cfq_pool, new_cfqq);

        atomic_inc(&cfqq->ref);
out:
        WARN_ON((gfp_mask & __GFP_WAIT) && !cfqq);
        return cfqq;
}

/*
 * Setup general io context and cfq io context. There can be several cfq
 * io contexts per general io context, if this process is doing io to more
 * than one device managed by cfq. Note that caller is holding a reference to
 * cfqq, so we don't need to worry about it disappearing
 */
static struct cfq_io_context *
cfq_get_io_context(struct cfq_data *cfqd, pid_t pid, int gfp_mask)
{
        struct io_context *ioc = NULL;
        struct cfq_io_context *cic;

        might_sleep_if(gfp_mask & __GFP_WAIT);

        ioc = get_io_context(gfp_mask);
        if (!ioc)
                return NULL;

        if ((cic = ioc->cic) == NULL) {
                cic = cfq_alloc_io_context(cfqd, gfp_mask);

                if (cic == NULL)
                        goto err;

                /*
                 * manually increment generic io_context usage count, it
                 * cannot go away since we are already holding one ref to it
                 */
                ioc->cic = cic;
                ioc->set_ioprio = cfq_ioc_set_ioprio;
                cic->ioc = ioc;
                cic->key = cfqd;
                atomic_inc(&cfqd->ref);
        } else {
                struct cfq_io_context *__cic;

                /*
                 * the first cic on the list is actually the head itself
                 */
                if (cic->key == cfqd)
                        goto out;

                /*
                 * cic exists, check if we already are there. linear search
                 * should be ok here, the list will usually not be more than
                 * 1 or a few entries long
                 */
                list_for_each_entry(__cic, &cic->list, list) {
                        /*
                         * this process is already holding a reference to
                         * this queue, so no need to get one more
                         */
                        if (__cic->key == cfqd) {
                                cic = __cic;
                                goto out;
                        }
                }

                /*
                 * nope, process doesn't have a cic assoicated with this
                 * cfqq yet. get a new one and add to list
                 */
                __cic = cfq_alloc_io_context(cfqd, gfp_mask);
                if (__cic == NULL)
                        goto err;

                __cic->ioc = ioc;
                __cic->key = cfqd;
                atomic_inc(&cfqd->ref);
                list_add(&__cic->list, &cic->list);
                cic = __cic;
        }

out:
        return cic;
err:
        put_io_context(ioc);
        return NULL;
}

static void
cfq_update_io_thinktime(struct cfq_data *cfqd, struct cfq_io_context *cic)
{
        unsigned long elapsed, ttime;

        /*
         * if this context already has stuff queued, thinktime is from
         * last queue not last end
         */
#if 0
        if (time_after(cic->last_end_request, cic->last_queue))
                elapsed = jiffies - cic->last_end_request;
        else
                elapsed = jiffies - cic->last_queue;
#else
                elapsed = jiffies - cic->last_end_request;
#endif

        ttime = min(elapsed, 2UL * cfqd->cfq_slice_idle);

        cic->ttime_samples = (7*cic->ttime_samples + 256) / 8;
        cic->ttime_total = (7*cic->ttime_total + 256*ttime) / 8;
        cic->ttime_mean = (cic->ttime_total + 128) / cic->ttime_samples;
}

#define sample_valid(samples)   ((samples) > 80)

/*
 * Disable idle window if the process thinks too long or seeks so much that
 * it doesn't matter
 */
static void
cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                       struct cfq_io_context *cic)
{
        int enable_idle = cfq_cfqq_idle_window(cfqq);

        if (!cic->ioc->task || !cfqd->cfq_slice_idle)
                enable_idle = 0;
        else if (sample_valid(cic->ttime_samples)) {
                if (cic->ttime_mean > cfqd->cfq_slice_idle)
                        enable_idle = 0;
                else
                        enable_idle = 1;
        }

        if (enable_idle)
                cfq_mark_cfqq_idle_window(cfqq);
        else
                cfq_clear_cfqq_idle_window(cfqq);
}


/*
 * Check if new_cfqq should preempt the currently active queue. Return 0 for
 * no or if we aren't sure, a 1 will cause a preempt.
 */
static int
cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
                   struct cfq_rq *crq)
{
        struct cfq_queue *cfqq = cfqd->active_queue;

        if (cfq_class_idle(new_cfqq))
                return 0;

        if (!cfqq)
                return 1;

        if (cfq_class_idle(cfqq))
                return 1;
        if (!cfq_cfqq_wait_request(new_cfqq))
                return 0;
        /*
         * if it doesn't have slice left, forget it
         */
        if (new_cfqq->slice_left < cfqd->cfq_slice_idle)
                return 0;
        if (cfq_crq_is_sync(crq) && !cfq_cfqq_sync(cfqq))
                return 1;

        return 0;
}

/*
 * cfqq preempts the active queue. if we allowed preempt with no slice left,
 * let it have half of its nominal slice.
 */
static void cfq_preempt_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        struct cfq_queue *__cfqq, *next;

        list_for_each_entry_safe(__cfqq, next, &cfqd->cur_rr, cfq_list)
                cfq_resort_rr_list(__cfqq, 1);

        if (!cfqq->slice_left)
                cfqq->slice_left = cfq_prio_to_slice(cfqd, cfqq) / 2;

        cfqq->slice_end = cfqq->slice_left + jiffies;
        __cfq_slice_expired(cfqd, cfqq, 1);
        __cfq_set_active_queue(cfqd, cfqq);
}

/*
 * should really be a ll_rw_blk.c helper
 */
static void cfq_start_queueing(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        request_queue_t *q = cfqd->queue;

        if (!blk_queue_plugged(q))
                q->request_fn(q);
        else
                __generic_unplug_device(q);
}

/*
 * Called when a new fs request (crq) is added (to cfqq). Check if there's
 * something we should do about it
 */
static void
cfq_crq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                 struct cfq_rq *crq)
{
        struct cfq_io_context *cic;

        cfqq->next_crq = cfq_choose_req(cfqd, cfqq->next_crq, crq);

        /*
         * we never wait for an async request and we don't allow preemption
         * of an async request. so just return early
         */
        if (!cfq_crq_is_sync(crq))
                return;

        cic = crq->io_context;

        cfq_update_io_thinktime(cfqd, cic);
        cfq_update_idle_window(cfqd, cfqq, cic);

        cic->last_queue = jiffies;

        if (cfqq == cfqd->active_queue) {
                /*
                 * if we are waiting for a request for this queue, let it rip
                 * immediately and flag that we must not expire this queue
                 * just now
                 */
                if (cfq_cfqq_wait_request(cfqq)) {
                        cfq_mark_cfqq_must_dispatch(cfqq);
                        del_timer(&cfqd->idle_slice_timer);
                        cfq_start_queueing(cfqd, cfqq);
                }
        } else if (cfq_should_preempt(cfqd, cfqq, crq)) {
                /*
                 * not the active queue - expire current slice if it is
                 * idle and has expired it's mean thinktime or this new queue
                 * has some old slice time left and is of higher priority
                 */
                cfq_preempt_queue(cfqd, cfqq);
                cfq_mark_cfqq_must_dispatch(cfqq);
                cfq_start_queueing(cfqd, cfqq);
        }
}

static void cfq_insert_request(request_queue_t *q, struct request *rq)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct cfq_rq *crq = RQ_DATA(rq);
        struct cfq_queue *cfqq = crq->cfq_queue;

        cfq_init_prio_data(cfqq);

        cfq_add_crq_rb(crq);

        list_add_tail(&rq->queuelist, &cfqq->fifo);

        if (rq_mergeable(rq)) {
                cfq_add_crq_hash(cfqd, crq);

                if (!cfqd->queue->last_merge)
                        cfqd->queue->last_merge = rq;
        }

        cfq_crq_enqueued(cfqd, cfqq, crq);
}

static void cfq_completed_request(request_queue_t *q, struct request *rq)
{
        struct cfq_rq *crq = RQ_DATA(rq);
        struct cfq_queue *cfqq = crq->cfq_queue;
        struct cfq_data *cfqd = cfqq->cfqd;
        const int sync = cfq_crq_is_sync(crq);
        unsigned long now;

        now = jiffies;

        WARN_ON(!cfqd->rq_in_driver);
        WARN_ON(!cfqq->on_dispatch[sync]);
        cfqd->rq_in_driver--;
        cfqq->on_dispatch[sync]--;

        if (!cfq_class_idle(cfqq))
                cfqd->last_end_request = now;

        if (!cfq_cfqq_dispatched(cfqq)) {
                if (cfq_cfqq_on_rr(cfqq)) {
                        cfqq->service_last = now;
                        cfq_resort_rr_list(cfqq, 0);
                }
                if (cfq_cfqq_expired(cfqq)) {
                        __cfq_slice_expired(cfqd, cfqq, 0);
                        cfq_schedule_dispatch(cfqd);
                }
        }

        if (cfq_crq_is_sync(crq))
                crq->io_context->last_end_request = now;
}

static struct request *
cfq_former_request(request_queue_t *q, struct request *rq)
{
        struct cfq_rq *crq = RQ_DATA(rq);
        struct rb_node *rbprev = rb_prev(&crq->rb_node);

        if (rbprev)
                return rb_entry_crq(rbprev)->request;

        return NULL;
}

static struct request *
cfq_latter_request(request_queue_t *q, struct request *rq)
{
        struct cfq_rq *crq = RQ_DATA(rq);
        struct rb_node *rbnext = rb_next(&crq->rb_node);

        if (rbnext)
                return rb_entry_crq(rbnext)->request;

        return NULL;
}

/*
 * we temporarily boost lower priority queues if they are holding fs exclusive
 * resources. they are boosted to normal prio (CLASS_BE/4)
 */
static void cfq_prio_boost(struct cfq_queue *cfqq)
{
        const int ioprio_class = cfqq->ioprio_class;
        const int ioprio = cfqq->ioprio;

        if (has_fs_excl()) {
                /*
                 * boost idle prio on transactions that would lock out other
                 * users of the filesystem
                 */
                if (cfq_class_idle(cfqq))
                        cfqq->ioprio_class = IOPRIO_CLASS_BE;
                if (cfqq->ioprio > IOPRIO_NORM)
                        cfqq->ioprio = IOPRIO_NORM;
        } else {
                /*
                 * check if we need to unboost the queue
                 */
                if (cfqq->ioprio_class != cfqq->org_ioprio_class)
                        cfqq->ioprio_class = cfqq->org_ioprio_class;
                if (cfqq->ioprio != cfqq->org_ioprio)
                        cfqq->ioprio = cfqq->org_ioprio;
        }

        /*
         * refile between round-robin lists if we moved the priority class
         */
        if ((ioprio_class != cfqq->ioprio_class || ioprio != cfqq->ioprio) &&
            cfq_cfqq_on_rr(cfqq))
                cfq_resort_rr_list(cfqq, 0);
}

static inline pid_t cfq_queue_pid(struct task_struct *task, int rw)
{
        if (rw == READ || process_sync(task))
                return task->pid;

        return CFQ_KEY_ASYNC;
}

static inline int
__cfq_may_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                struct task_struct *task, int rw)
{
#if 1
        if ((cfq_cfqq_wait_request(cfqq) || cfq_cfqq_must_alloc(cfqq)) &&
            !cfq_cfqq_must_alloc_slice(cfqq)) {
                cfq_mark_cfqq_must_alloc_slice(cfqq);
                return ELV_MQUEUE_MUST;
        }

        return ELV_MQUEUE_MAY;
#else
        if (!cfqq || task->flags & PF_MEMALLOC)
                return ELV_MQUEUE_MAY;
        if (!cfqq->allocated[rw] || cfq_cfqq_must_alloc(cfqq)) {
                if (cfq_cfqq_wait_request(cfqq))
                        return ELV_MQUEUE_MUST;

                /*
                 * only allow 1 ELV_MQUEUE_MUST per slice, otherwise we
                 * can quickly flood the queue with writes from a single task
                 */
                if (rw == READ || !cfq_cfqq_must_alloc_slice(cfqq)) {
                        cfq_mark_cfqq_must_alloc_slice(cfqq);
                        return ELV_MQUEUE_MUST;
                }

                return ELV_MQUEUE_MAY;
        }
        if (cfq_class_idle(cfqq))
                return ELV_MQUEUE_NO;
        if (cfqq->allocated[rw] >= cfqd->max_queued) {
                struct io_context *ioc = get_io_context(GFP_ATOMIC);
                int ret = ELV_MQUEUE_NO;

                if (ioc && ioc->nr_batch_requests)
                        ret = ELV_MQUEUE_MAY;

                put_io_context(ioc);
                return ret;
        }

        return ELV_MQUEUE_MAY;
#endif
}

static int cfq_may_queue(request_queue_t *q, int rw, struct bio *bio)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct task_struct *tsk = current;
        struct cfq_queue *cfqq;

        /*
         * don't force setup of a queue from here, as a call to may_queue
         * does not necessarily imply that a request actually will be queued.
         * so just lookup a possibly existing queue, or return 'may queue'
         * if that fails
         */
        cfqq = cfq_find_cfq_hash(cfqd, cfq_queue_pid(tsk, rw), tsk->ioprio);
        if (cfqq) {
                cfq_init_prio_data(cfqq);
                cfq_prio_boost(cfqq);

                return __cfq_may_queue(cfqd, cfqq, tsk, rw);
        }

        return ELV_MQUEUE_MAY;
}

static void cfq_check_waiters(request_queue_t *q, struct cfq_queue *cfqq)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct request_list *rl = &q->rq;

        if (cfqq->allocated[READ] <= cfqd->max_queued || cfqd->rq_starved) {
                smp_mb();
                if (waitqueue_active(&rl->wait[READ]))
                        wake_up(&rl->wait[READ]);
        }

        if (cfqq->allocated[WRITE] <= cfqd->max_queued || cfqd->rq_starved) {
                smp_mb();
                if (waitqueue_active(&rl->wait[WRITE]))
                        wake_up(&rl->wait[WRITE]);
        }
}

/*
 * queue lock held here
 */
static void cfq_put_request(request_queue_t *q, struct request *rq)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct cfq_rq *crq = RQ_DATA(rq);

        if (crq) {
                struct cfq_queue *cfqq = crq->cfq_queue;
                const int rw = rq_data_dir(rq);

                BUG_ON(!cfqq->allocated[rw]);
                cfqq->allocated[rw]--;

                put_io_context(crq->io_context->ioc);

                mempool_free(crq, cfqd->crq_pool);
                rq->elevator_private = NULL;

                cfq_check_waiters(q, cfqq);
                cfq_put_queue(cfqq);
        }
}

/*
 * Allocate cfq data structures associated with this request.
 */
static int
cfq_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
                int gfp_mask)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct task_struct *tsk = current;
        struct cfq_io_context *cic;
        const int rw = rq_data_dir(rq);
        pid_t key = cfq_queue_pid(tsk, rw);
        struct cfq_queue *cfqq;
        struct cfq_rq *crq;
        unsigned long flags;

        might_sleep_if(gfp_mask & __GFP_WAIT);

        cic = cfq_get_io_context(cfqd, key, gfp_mask);

        spin_lock_irqsave(q->queue_lock, flags);

        if (!cic)
                goto queue_fail;

        if (!cic->cfqq) {
                cfqq = cfq_get_queue(cfqd, key, tsk->ioprio, gfp_mask);
                if (!cfqq)
                        goto queue_fail;

                cic->cfqq = cfqq;
        } else
                cfqq = cic->cfqq;

        cfqq->allocated[rw]++;
        cfq_clear_cfqq_must_alloc(cfqq);
        cfqd->rq_starved = 0;
        atomic_inc(&cfqq->ref);
        spin_unlock_irqrestore(q->queue_lock, flags);

        crq = mempool_alloc(cfqd->crq_pool, gfp_mask);
        if (crq) {
                RB_CLEAR(&crq->rb_node);
                crq->rb_key = 0;
                crq->request = rq;
                INIT_HLIST_NODE(&crq->hash);
                crq->cfq_queue = cfqq;
                crq->io_context = cic;

                if (rw == READ || process_sync(tsk))
                        cfq_mark_crq_is_sync(crq);
                else
                        cfq_clear_crq_is_sync(crq);

                rq->elevator_private = crq;
                return 0;
        }

        spin_lock_irqsave(q->queue_lock, flags);
        cfqq->allocated[rw]--;
        if (!(cfqq->allocated[0] + cfqq->allocated[1]))
                cfq_mark_cfqq_must_alloc(cfqq);
        cfq_put_queue(cfqq);
queue_fail:
        if (cic)
                put_io_context(cic->ioc);
        /*
         * mark us rq allocation starved. we need to kickstart the process
         * ourselves if there are no pending requests that can do it for us.
         * that would be an extremely rare OOM situation
         */
        cfqd->rq_starved = 1;
        cfq_schedule_dispatch(cfqd);
        spin_unlock_irqrestore(q->queue_lock, flags);
        return 1;
}

static void cfq_kick_queue(void *data)
{
        request_queue_t *q = data;
        struct cfq_data *cfqd = q->elevator->elevator_data;
        unsigned long flags;

        spin_lock_irqsave(q->queue_lock, flags);

        if (cfqd->rq_starved) {
                struct request_list *rl = &q->rq;

                /*
                 * we aren't guaranteed to get a request after this, but we
                 * have to be opportunistic
                 */
                smp_mb();
                if (waitqueue_active(&rl->wait[READ]))
                        wake_up(&rl->wait[READ]);
                if (waitqueue_active(&rl->wait[WRITE]))
                        wake_up(&rl->wait[WRITE]);
        }

        blk_remove_plug(q);
        q->request_fn(q);
        spin_unlock_irqrestore(q->queue_lock, flags);
}

/*
 * Timer running if the active_queue is currently idling inside its time slice
 */
static void cfq_idle_slice_timer(unsigned long data)
{
        struct cfq_data *cfqd = (struct cfq_data *) data;
        struct cfq_queue *cfqq;
        unsigned long flags;

        spin_lock_irqsave(cfqd->queue->queue_lock, flags);

        if ((cfqq = cfqd->active_queue) != NULL) {
                unsigned long now = jiffies;

                /*
                 * expired
                 */
                if (time_after(now, cfqq->slice_end))
                        goto expire;

                /*
                 * only expire and reinvoke request handler, if there are
                 * other queues with pending requests
                 */
                if (!cfqd->busy_queues) {
                        cfqd->idle_slice_timer.expires = min(now + cfqd->cfq_slice_idle, cfqq->slice_end);
                        add_timer(&cfqd->idle_slice_timer);
                        goto out_cont;
                }

                /*
                 * not expired and it has a request pending, let it dispatch
                 */
                if (!RB_EMPTY(&cfqq->sort_list)) {
                        cfq_mark_cfqq_must_dispatch(cfqq);
                        goto out_kick;
                }
        }
expire:
        cfq_slice_expired(cfqd, 0);
out_kick:
        cfq_schedule_dispatch(cfqd);
out_cont:
        spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
}

/*
 * Timer running if an idle class queue is waiting for service
 */
static void cfq_idle_class_timer(unsigned long data)
{
        struct cfq_data *cfqd = (struct cfq_data *) data;
        unsigned long flags, end;

        spin_lock_irqsave(cfqd->queue->queue_lock, flags);

        /*
         * race with a non-idle queue, reset timer
         */
        end = cfqd->last_end_request + CFQ_IDLE_GRACE;
        if (!time_after_eq(jiffies, end)) {
                cfqd->idle_class_timer.expires = end;
                add_timer(&cfqd->idle_class_timer);
        } else
                cfq_schedule_dispatch(cfqd);

        spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
}

static void cfq_shutdown_timer_wq(struct cfq_data *cfqd)
{
        del_timer_sync(&cfqd->idle_slice_timer);
        del_timer_sync(&cfqd->idle_class_timer);
        blk_sync_queue(cfqd->queue);
}

static void cfq_put_cfqd(struct cfq_data *cfqd)
{
        request_queue_t *q = cfqd->queue;

        if (!atomic_dec_and_test(&cfqd->ref))
                return;

        blk_put_queue(q);

        cfq_shutdown_timer_wq(cfqd);
        q->elevator->elevator_data = NULL;

        mempool_destroy(cfqd->crq_pool);
        kfree(cfqd->crq_hash);
        kfree(cfqd->cfq_hash);
        kfree(cfqd);
}

static void cfq_exit_queue(elevator_t *e)
{
        struct cfq_data *cfqd = e->elevator_data;

        cfq_shutdown_timer_wq(cfqd);
        cfq_put_cfqd(cfqd);
}

static int cfq_init_queue(request_queue_t *q, elevator_t *e)
{
        struct cfq_data *cfqd;
        int i;

        cfqd = kmalloc(sizeof(*cfqd), GFP_KERNEL);
        if (!cfqd)
                return -ENOMEM;

        memset(cfqd, 0, sizeof(*cfqd));

        for (i = 0; i < CFQ_PRIO_LISTS; i++)
                INIT_LIST_HEAD(&cfqd->rr_list[i]);

        INIT_LIST_HEAD(&cfqd->busy_rr);
        INIT_LIST_HEAD(&cfqd->cur_rr);
        INIT_LIST_HEAD(&cfqd->idle_rr);
        INIT_LIST_HEAD(&cfqd->empty_list);

        cfqd->crq_hash = kmalloc(sizeof(struct hlist_head) * CFQ_MHASH_ENTRIES, GFP_KERNEL);
        if (!cfqd->crq_hash)
                goto out_crqhash;

        cfqd->cfq_hash = kmalloc(sizeof(struct hlist_head) * CFQ_QHASH_ENTRIES, GFP_KERNEL);
        if (!cfqd->cfq_hash)
                goto out_cfqhash;

        cfqd->crq_pool = mempool_create(BLKDEV_MIN_RQ, mempool_alloc_slab, mempool_free_slab, crq_pool);
        if (!cfqd->crq_pool)
                goto out_crqpool;

        for (i = 0; i < CFQ_MHASH_ENTRIES; i++)
                INIT_HLIST_HEAD(&cfqd->crq_hash[i]);
        for (i = 0; i < CFQ_QHASH_ENTRIES; i++)
                INIT_HLIST_HEAD(&cfqd->cfq_hash[i]);

        e->elevator_data = cfqd;

        cfqd->queue = q;
        atomic_inc(&q->refcnt);

        cfqd->max_queued = q->nr_requests / 4;
        q->nr_batching = cfq_queued;

        init_timer(&cfqd->idle_slice_timer);
        cfqd->idle_slice_timer.function = cfq_idle_slice_timer;
        cfqd->idle_slice_timer.data = (unsigned long) cfqd;

        init_timer(&cfqd->idle_class_timer);
        cfqd->idle_class_timer.function = cfq_idle_class_timer;
        cfqd->idle_class_timer.data = (unsigned long) cfqd;

        INIT_WORK(&cfqd->unplug_work, cfq_kick_queue, q);

        atomic_set(&cfqd->ref, 1);

        cfqd->cfq_queued = cfq_queued;
        cfqd->cfq_quantum = cfq_quantum;
        cfqd->cfq_fifo_expire[0] = cfq_fifo_expire[0];
        cfqd->cfq_fifo_expire[1] = cfq_fifo_expire[1];
        cfqd->cfq_back_max = cfq_back_max;
        cfqd->cfq_back_penalty = cfq_back_penalty;
        cfqd->cfq_slice[0] = cfq_slice_async;
        cfqd->cfq_slice[1] = cfq_slice_sync;
        cfqd->cfq_slice_async_rq = cfq_slice_async_rq;
        cfqd->cfq_slice_idle = cfq_slice_idle;
        cfqd->cfq_max_depth = cfq_max_depth;

        return 0;
out_crqpool:
        kfree(cfqd->cfq_hash);
out_cfqhash:
        kfree(cfqd->crq_hash);
out_crqhash:
        kfree(cfqd);
        return -ENOMEM;
}

static void cfq_slab_kill(void)
{
        if (crq_pool)
                kmem_cache_destroy(crq_pool);
        if (cfq_pool)
                kmem_cache_destroy(cfq_pool);
        if (cfq_ioc_pool)
                kmem_cache_destroy(cfq_ioc_pool);
}

static int __init cfq_slab_setup(void)
{
        crq_pool = kmem_cache_create("crq_pool", sizeof(struct cfq_rq), 0, 0,
                                        NULL, NULL);
        if (!crq_pool)
                goto fail;

        cfq_pool = kmem_cache_create("cfq_pool", sizeof(struct cfq_queue), 0, 0,
                                        NULL, NULL);
        if (!cfq_pool)
                goto fail;

        cfq_ioc_pool = kmem_cache_create("cfq_ioc_pool",
                        sizeof(struct cfq_io_context), 0, 0, NULL, NULL);
        if (!cfq_ioc_pool)
                goto fail;

        return 0;
fail:
        cfq_slab_kill();
        return -ENOMEM;
}

/*
 * sysfs parts below -->
 */
struct cfq_fs_entry {
        struct attribute attr;
        ssize_t (*show)(struct cfq_data *, char *);
        ssize_t (*store)(struct cfq_data *, const char *, size_t);
};

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

static ssize_t
cfq_var_store(unsigned int *var, const char *page, size_t count)
{
        char *p = (char *) page;

        *var = simple_strtoul(p, &p, 10);
        return count;
}

#define SHOW_FUNCTION(__FUNC, __VAR, __CONV)                            \
static ssize_t __FUNC(struct cfq_data *cfqd, char *page)                \
{                                                                       \
        unsigned int __data = __VAR;                                    \
        if (__CONV)                                                     \
                __data = jiffies_to_msecs(__data);                      \
        return cfq_var_show(__data, (page));                            \
}
SHOW_FUNCTION(cfq_quantum_show, cfqd->cfq_quantum, 0);
SHOW_FUNCTION(cfq_queued_show, cfqd->cfq_queued, 0);
SHOW_FUNCTION(cfq_fifo_expire_sync_show, cfqd->cfq_fifo_expire[1], 1);
SHOW_FUNCTION(cfq_fifo_expire_async_show, cfqd->cfq_fifo_expire[0], 1);
SHOW_FUNCTION(cfq_back_max_show, cfqd->cfq_back_max, 0);
SHOW_FUNCTION(cfq_back_penalty_show, cfqd->cfq_back_penalty, 0);
SHOW_FUNCTION(cfq_slice_idle_show, cfqd->cfq_slice_idle, 1);
SHOW_FUNCTION(cfq_slice_sync_show, cfqd->cfq_slice[1], 1);
SHOW_FUNCTION(cfq_slice_async_show, cfqd->cfq_slice[0], 1);
SHOW_FUNCTION(cfq_slice_async_rq_show, cfqd->cfq_slice_async_rq, 0);
SHOW_FUNCTION(cfq_max_depth_show, cfqd->cfq_max_depth, 0);
#undef SHOW_FUNCTION

#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)                 \
static ssize_t __FUNC(struct cfq_data *cfqd, const char *page, size_t count)    \
{                                                                       \
        unsigned int __data;                                            \
        int ret = cfq_var_store(&__data, (page), count);                \
        if (__data < (MIN))                                             \
                __data = (MIN);                                         \
        else if (__data > (MAX))                                        \
                __data = (MAX);                                         \
        if (__CONV)                                                     \
                *(__PTR) = msecs_to_jiffies(__data);                    \
        else                                                            \
                *(__PTR) = __data;                                      \
        return ret;                                                     \
}
STORE_FUNCTION(cfq_quantum_store, &cfqd->cfq_quantum, 1, UINT_MAX, 0);
STORE_FUNCTION(cfq_queued_store, &cfqd->cfq_queued, 1, UINT_MAX, 0);
STORE_FUNCTION(cfq_fifo_expire_sync_store, &cfqd->cfq_fifo_expire[1], 1, UINT_MAX, 1);
STORE_FUNCTION(cfq_fifo_expire_async_store, &cfqd->cfq_fifo_expire[0], 1, UINT_MAX, 1);
STORE_FUNCTION(cfq_back_max_store, &cfqd->cfq_back_max, 0, UINT_MAX, 0);
STORE_FUNCTION(cfq_back_penalty_store, &cfqd->cfq_back_penalty, 1, UINT_MAX, 0);
STORE_FUNCTION(cfq_slice_idle_store, &cfqd->cfq_slice_idle, 0, UINT_MAX, 1);
STORE_FUNCTION(cfq_slice_sync_store, &cfqd->cfq_slice[1], 1, UINT_MAX, 1);
STORE_FUNCTION(cfq_slice_async_store, &cfqd->cfq_slice[0], 1, UINT_MAX, 1);
STORE_FUNCTION(cfq_slice_async_rq_store, &cfqd->cfq_slice_async_rq, 1, UINT_MAX, 0);
STORE_FUNCTION(cfq_max_depth_store, &cfqd->cfq_max_depth, 1, UINT_MAX, 0);
#undef STORE_FUNCTION

static struct cfq_fs_entry cfq_quantum_entry = {
        .attr = {.name = "quantum", .mode = S_IRUGO | S_IWUSR },
        .show = cfq_quantum_show,
        .store = cfq_quantum_store,
};
static struct cfq_fs_entry cfq_queued_entry = {
        .attr = {.name = "queued", .mode = S_IRUGO | S_IWUSR },
        .show = cfq_queued_show,
        .store = cfq_queued_store,
};
static struct cfq_fs_entry cfq_fifo_expire_sync_entry = {
        .attr = {.name = "fifo_expire_sync", .mode = S_IRUGO | S_IWUSR },
        .show = cfq_fifo_expire_sync_show,
        .store = cfq_fifo_expire_sync_store,
};
static struct cfq_fs_entry cfq_fifo_expire_async_entry = {
        .attr = {.name = "fifo_expire_async", .mode = S_IRUGO | S_IWUSR },
        .show = cfq_fifo_expire_async_show,
        .store = cfq_fifo_expire_async_store,
};
static struct cfq_fs_entry cfq_back_max_entry = {
        .attr = {.name = "back_seek_max", .mode = S_IRUGO | S_IWUSR },
        .show = cfq_back_max_show,
        .store = cfq_back_max_store,
};
static struct cfq_fs_entry cfq_back_penalty_entry = {
        .attr = {.name = "back_seek_penalty", .mode = S_IRUGO | S_IWUSR },
        .show = cfq_back_penalty_show,
        .store = cfq_back_penalty_store,
};
static struct cfq_fs_entry cfq_slice_sync_entry = {
        .attr = {.name = "slice_sync", .mode = S_IRUGO | S_IWUSR },
        .show = cfq_slice_sync_show,
        .store = cfq_slice_sync_store,
};
static struct cfq_fs_entry cfq_slice_async_entry = {
        .attr = {.name = "slice_async", .mode = S_IRUGO | S_IWUSR },
        .show = cfq_slice_async_show,
        .store = cfq_slice_async_store,
};
static struct cfq_fs_entry cfq_slice_async_rq_entry = {
        .attr = {.name = "slice_async_rq", .mode = S_IRUGO | S_IWUSR },
        .show = cfq_slice_async_rq_show,
        .store = cfq_slice_async_rq_store,
};
static struct cfq_fs_entry cfq_slice_idle_entry = {
        .attr = {.name = "slice_idle", .mode = S_IRUGO | S_IWUSR },
        .show = cfq_slice_idle_show,
        .store = cfq_slice_idle_store,
};
static struct cfq_fs_entry cfq_max_depth_entry = {
        .attr = {.name = "max_depth", .mode = S_IRUGO | S_IWUSR },
        .show = cfq_max_depth_show,
        .store = cfq_max_depth_store,
};

static struct attribute *default_attrs[] = {
        &cfq_quantum_entry.attr,
        &cfq_queued_entry.attr,
        &cfq_fifo_expire_sync_entry.attr,
        &cfq_fifo_expire_async_entry.attr,
        &cfq_back_max_entry.attr,
        &cfq_back_penalty_entry.attr,
        &cfq_slice_sync_entry.attr,
        &cfq_slice_async_entry.attr,
        &cfq_slice_async_rq_entry.attr,
        &cfq_slice_idle_entry.attr,
        &cfq_max_depth_entry.attr,
        NULL,
};

#define to_cfq(atr) container_of((atr), struct cfq_fs_entry, attr)

static ssize_t
cfq_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
{
        elevator_t *e = container_of(kobj, elevator_t, kobj);
        struct cfq_fs_entry *entry = to_cfq(attr);

        if (!entry->show)
                return -EIO;

        return entry->show(e->elevator_data, page);
}

static ssize_t
cfq_attr_store(struct kobject *kobj, struct attribute *attr,
               const char *page, size_t length)
{
        elevator_t *e = container_of(kobj, elevator_t, kobj);
        struct cfq_fs_entry *entry = to_cfq(attr);

        if (!entry->store)
                return -EIO;

        return entry->store(e->elevator_data, page, length);
}

static struct sysfs_ops cfq_sysfs_ops = {
        .show   = cfq_attr_show,
        .store  = cfq_attr_store,
};

static struct kobj_type cfq_ktype = {
        .sysfs_ops      = &cfq_sysfs_ops,
        .default_attrs  = default_attrs,
};

static struct elevator_type iosched_cfq = {
        .ops = {
                .elevator_merge_fn =            cfq_merge,
                .elevator_merged_fn =           cfq_merged_request,
                .elevator_merge_req_fn =        cfq_merged_requests,
                .elevator_dispatch_fn =         cfq_dispatch_requests,
                .elevator_add_req_fn =          cfq_insert_request,
                .elevator_activate_req_fn =     cfq_activate_request,
                .elevator_deactivate_req_fn =   cfq_deactivate_request,
                .elevator_queue_empty_fn =      cfq_queue_empty,
                .elevator_completed_req_fn =    cfq_completed_request,
                .elevator_former_req_fn =       cfq_former_request,
                .elevator_latter_req_fn =       cfq_latter_request,
                .elevator_set_req_fn =          cfq_set_request,
                .elevator_put_req_fn =          cfq_put_request,
                .elevator_may_queue_fn =        cfq_may_queue,
                .elevator_init_fn =             cfq_init_queue,
                .elevator_exit_fn =             cfq_exit_queue,
        },
        .elevator_ktype =       &cfq_ktype,
        .elevator_name =        "cfq",
        .elevator_owner =       THIS_MODULE,
};

static int __init cfq_init(void)
{
        int ret;

        /*
         * could be 0 on HZ < 1000 setups
         */
        if (!cfq_slice_async)
                cfq_slice_async = 1;
        if (!cfq_slice_idle)
                cfq_slice_idle = 1;

        if (cfq_slab_setup())
                return -ENOMEM;

        ret = elv_register(&iosched_cfq);
        if (ret)
                cfq_slab_kill();

        return ret;
}

static void __exit cfq_exit(void)
{
        struct task_struct *g, *p;
        unsigned long flags;

        read_lock_irqsave(&tasklist_lock, flags);

        /*
         * iterate each process in the system, removing our io_context
         */
        do_each_thread(g, p) {
                struct io_context *ioc = p->io_context;

                if (ioc && ioc->cic) {
                        ioc->cic->exit(ioc->cic);
                        cfq_free_io_context(ioc->cic);
                        ioc->cic = NULL;
                }
        } while_each_thread(g, p);

        read_unlock_irqrestore(&tasklist_lock, flags);

        cfq_slab_kill();
        elv_unregister(&iosched_cfq);
}

module_init(cfq_init);
module_exit(cfq_exit);

MODULE_AUTHOR("Jens Axboe");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Completely Fair Queueing IO scheduler");