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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/module.h>
#include <linux/blkdev.h>
#include <linux/elevator.h>
#include <linux/hash.h>
#include <linux/rbtree.h>
#include <linux/ioprio.h>

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

static const int cfq_slice_sync = HZ / 10;
static int cfq_slice_async = HZ / 25;
static const int cfq_slice_async_rq = 2;
static int cfq_slice_idle = HZ / 125;

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

#define CFQ_KEY_ASYNC         (0)

static DEFINE_SPINLOCK(cfq_exit_lock);

/*
 * 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_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;

static atomic_t ioc_count = ATOMIC_INIT(0);
static struct completion *ioc_gone;

#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])

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

/*
 * Per block device queue structure
 */
struct cfq_data {
      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;

      mempool_t *crq_pool;

      int rq_in_driver;
      int hw_tag;

      /*
       * 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;

      struct list_head cic_list;
};

/*
 * 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,
};

#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);
#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 struct cfq_queue *cfq_get_queue(struct cfq_data *cfqd, unsigned int key, struct task_struct *tsk, gfp_t gfp_mask);

/*
 * 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 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->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;
}

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

      return CFQ_KEY_ASYNC;
}

/*
 * 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 is 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;
      unsigned long back_max;
#define CFQ_RQ1_WRAP    0x01 /* request 1 wraps */
#define CFQ_RQ2_WRAP    0x02 /* request 2 wraps */
      unsigned wrap = 0; /* bit mask: requests behind the disk head? */

      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
            wrap |= CFQ_RQ1_WRAP;

      if (s2 >= last)
            d2 = s2 - last;
      else if (s2 + back_max >= last)
            d2 = (last - s2) * cfqd->cfq_back_penalty;
      else
            wrap |= CFQ_RQ2_WRAP;

      /* Found required data */

      /*
       * By doing switch() on the bit mask "wrap" we avoid having to
       * check two variables for all permutations: --> faster!
       */
      switch (wrap) {
      case 0: /* common case for CFQ: crq1 and crq2 not wrapped */
            if (d1 < d2)
                  return crq1;
            else if (d2 < d1)
                  return crq2;
            else {
                  if (s1 >= s2)
                        return crq1;
                  else
                        return crq2;
            }

      case CFQ_RQ2_WRAP:
            return crq1;
      case CFQ_RQ1_WRAP:
            return crq2;
      case (CFQ_RQ1_WRAP|CFQ_RQ2_WRAP): /* both crqs wrapped */
      default:
            /*
             * Since both rqs are wrapped,
             * start with the one that's further behind head
             * (--> only *one* back seek required),
             * since back seek takes more time than forward.
             */
            if (s1 <= s2)
                  return 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, but insert at the back for fairness.
       */
      if (preempted || list == &cfqd->busy_rr) {
            if (preempted)
                  list = list->prev;

            list_add_tail(&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);

      if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&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_fmerge(struct cfq_data *cfqd, struct bio *bio)
{
      struct task_struct *tsk = current;
      pid_t key = cfq_queue_pid(tsk, bio_data_dir(bio));
      struct cfq_queue *cfqq;
      struct rb_node *n;
      sector_t sector;

      cfqq = cfq_find_cfq_hash(cfqd, key, tsk->ioprio);
      if (!cfqq)
            goto out;

      sector = bio->bi_sector + bio_sectors(bio);
      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++;

      /*
       * If the depth is larger 1, it really could be queueing. But lets
       * make the mark a little higher - idling could still be good for
       * low queueing, and a low queueing number could also just indicate
       * a SCSI mid layer like behaviour where limit+1 is often seen.
       */
      if (!cfqd->hw_tag && cfqd->rq_in_driver > 4)
            cfqd->hw_tag = 1;
}

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_del_crq_hash(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;

      __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_fmerge(cfqd, bio);
      if (__rq && elv_rq_merge_ok(__rq, bio)) {
            ret = ELEVATOR_FRONT_MERGE;
            goto out;
      }

      return ELEVATOR_NO_MERGE;
out:
      *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);
      }
}

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);
      }

      cfqd->active_queue = 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_schedule_dispatch(cfqd);
      }

      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(cfqq->slice_end, now))
            cfqq->slice_left = cfqq->slice_end - now;
      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)
            __cfq_slice_expired(cfqd, cfqq, preempted);
}

/*
 * 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 = 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 no new queues are available, check if the busy list has some
       * before falling back to idle io.
       */
      if (!cfqq && !list_empty(&cfqd->busy_rr))
            cfqq = list_entry_cfqq(cfqd->busy_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;
}

#define CIC_SEEKY(cic) ((cic)->seek_mean > (128 * 1024))

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

{
      struct cfq_io_context *cic;
      unsigned long sl;

      WARN_ON(!RB_EMPTY_ROOT(&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
       */
      cic = cfqd->active_cic;
      if (!cic || !cic->ioc->task)
            return 0;

      cfq_mark_cfqq_must_dispatch(cfqq);
      cfq_mark_cfqq_wait_request(cfqq);

      sl = min(cfqq->slice_end - 1, (unsigned long) cfqd->cfq_slice_idle);

      /*
       * we don't want to idle for seeks, but we do want to allow
       * fair distribution of slice time for a process doing back-to-back
       * seeks. so allow a little bit of time for him to submit a new rq
       */
      if (sample_valid(cic->seek_samples) && CIC_SEEKY(cic))
            sl = min(sl, msecs_to_jiffies(2));

      mod_timer(&cfqd->idle_slice_timer, jiffies + sl);
      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;
      struct request *rq;

      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);

      rq = list_entry(q->queue_head.prev, struct request, queuelist);
      cfqd->last_sector = rq->sector + rq->nr_sectors;
}

/*
 * 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)
{
      unsigned long now = jiffies;
      struct cfq_queue *cfqq;

      cfqq = cfqd->active_queue;
      if (!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_ROOT(&cfqq->sort_list))
            goto keep_queue;
      else if (cfq_cfqq_dispatched(cfqq)) {
            cfqq = NULL;
            goto keep_queue;
      } else if (cfq_cfqq_class_sync(cfqq)) {
            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_ROOT(&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_ROOT(&cfqq->sort_list))
                  break;

      } while (dispatched < max_dispatch);

      /*
       * if slice end isn't set yet, set it.
       */
      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_cfqq_idle_window(cfqq))
            cfq_slice_expired(cfqd, 0);

      return dispatched;
}

static int
cfq_forced_dispatch_cfqqs(struct list_head *list)
{
      struct cfq_queue *cfqq, *next;
      struct cfq_rq *crq;
      int dispatched;

      dispatched = 0;
      list_for_each_entry_safe(cfqq, next, list, cfq_list) {
            while ((crq = cfqq->next_crq)) {
                  cfq_dispatch_insert(cfqq->cfqd->queue, crq);
                  dispatched++;
            }
            BUG_ON(!list_empty(&cfqq->fifo));
      }

      return dispatched;
}

static int
cfq_forced_dispatch(struct cfq_data *cfqd)
{
      int i, dispatched = 0;

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

      dispatched += cfq_forced_dispatch_cfqqs(&cfqd->busy_rr);
      dispatched += cfq_forced_dispatch_cfqqs(&cfqd->cur_rr);
      dispatched += cfq_forced_dispatch_cfqqs(&cfqd->idle_rr);

      cfq_slice_expired(cfqd, 0);

      BUG_ON(cfqd->busy_queues);

      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, *prev_cfqq;
      int dispatched;

      if (!cfqd->busy_queues)
            return 0;

      if (unlikely(force))
            return cfq_forced_dispatch(cfqd);

      dispatched = 0;
      prev_cfqq = NULL;
      while ((cfqq = cfq_select_queue(cfqd)) != NULL) {
            int max_dispatch;

            /*
             * Don't repeat dispatch from the previous queue.
             */
            if (prev_cfqq == cfqq)
                  break;

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

            max_dispatch = cfqd->cfq_quantum;
            if (cfq_class_idle(cfqq))
                  max_dispatch = 1;

            dispatched += __cfq_dispatch_requests(cfqd, cfqq, max_dispatch);

            /*
             * If the dispatch cfqq has idling enabled and is still
             * the active queue, break out.
             */
            if (cfq_cfqq_idle_window(cfqq) && cfqd->active_queue)
                  break;

            prev_cfqq = cfqq;
      }

      return dispatched;
}

/*
 * 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);

      /*
       * 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;
      struct cfq_queue *__cfqq;

      hlist_for_each_entry(__cfqq, entry, hash_list, cfq_hash) {
            const unsigned short __p = IOPRIO_PRIO_VALUE(__cfqq->org_ioprio_class, __cfqq->org_ioprio);

            if (__cfqq->key == key && (__p == prio || !prio))
                  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 io_context *ioc)
{
      struct cfq_io_context *__cic;
      struct rb_node *n;
      int freed = 0;

      while ((n = rb_first(&ioc->cic_root)) != NULL) {
            __cic = rb_entry(n, struct cfq_io_context, rb_node);
            rb_erase(&__cic->rb_node, &ioc->cic_root);
            kmem_cache_free(cfq_ioc_pool, __cic);
            freed++;
      }

      if (atomic_sub_and_test(freed, &ioc_count) && ioc_gone)
            complete(ioc_gone);
}

static void cfq_trim(struct io_context *ioc)
{
      ioc->set_ioprio = NULL;
      cfq_free_io_context(ioc);
}

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

      if (!cfqd)
            return;

      q = cfqd->queue;

      WARN_ON(!irqs_disabled());

      spin_lock(q->queue_lock);

      if (cic->cfqq[ASYNC]) {
            if (unlikely(cic->cfqq[ASYNC] == cfqd->active_queue))
                  __cfq_slice_expired(cfqd, cic->cfqq[ASYNC], 0);
            cfq_put_queue(cic->cfqq[ASYNC]);
            cic->cfqq[ASYNC] = NULL;
      }

      if (cic->cfqq[SYNC]) {
            if (unlikely(cic->cfqq[SYNC] == cfqd->active_queue))
                  __cfq_slice_expired(cfqd, cic->cfqq[SYNC], 0);
            cfq_put_queue(cic->cfqq[SYNC]);
            cic->cfqq[SYNC] = NULL;
      }

      cic->key = NULL;
      list_del_init(&cic->queue_list);
      spin_unlock(q->queue_lock);
}

static void cfq_exit_io_context(struct io_context *ioc)
{
      struct cfq_io_context *__cic;
      unsigned long flags;
      struct rb_node *n;

      /*
       * put the reference this task is holding to the various queues
       */
      spin_lock_irqsave(&cfq_exit_lock, flags);

      n = rb_first(&ioc->cic_root);
      while (n != NULL) {
            __cic = rb_entry(n, struct cfq_io_context, rb_node);

            cfq_exit_single_io_context(__cic);
            n = rb_next(n);
      }

      spin_unlock_irqrestore(&cfq_exit_lock, flags);
}

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

      if (cic) {
            memset(cic, 0, sizeof(*cic));
            cic->last_end_request = jiffies;
            INIT_LIST_HEAD(&cic->queue_list);
            cic->dtor = cfq_free_io_context;
            cic->exit = cfq_exit_io_context;
            atomic_inc(&ioc_count);
      }

      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_io_context *cic)
{
      struct cfq_data *cfqd = cic->key;
      struct cfq_queue *cfqq;

      if (unlikely(!cfqd))
            return;

      spin_lock(cfqd->queue->queue_lock);

      cfqq = cic->cfqq[ASYNC];
      if (cfqq) {
            struct cfq_queue *new_cfqq;
            new_cfqq = cfq_get_queue(cfqd, CFQ_KEY_ASYNC, cic->ioc->task,
                               GFP_ATOMIC);
            if (new_cfqq) {
                  cic->cfqq[ASYNC] = new_cfqq;
                  cfq_put_queue(cfqq);
            }
      }

      cfqq = cic->cfqq[SYNC];
      if (cfqq)
            cfq_mark_cfqq_prio_changed(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;
      struct rb_node *n;

      spin_lock(&cfq_exit_lock);

      n = rb_first(&ioc->cic_root);
      while (n != NULL) {
            cic = rb_entry(n, struct cfq_io_context, rb_node);

            changed_ioprio(cic);
            n = rb_next(n);
      }

      spin_unlock(&cfq_exit_lock);

      return 0;
}

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

retry:
      ioprio = tsk->ioprio;
      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);
            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;
            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;
}

static void
cfq_drop_dead_cic(struct io_context *ioc, struct cfq_io_context *cic)
{
      spin_lock(&cfq_exit_lock);
      rb_erase(&cic->rb_node, &ioc->cic_root);
      list_del_init(&cic->queue_list);
      spin_unlock(&cfq_exit_lock);
      kmem_cache_free(cfq_ioc_pool, cic);
      atomic_dec(&ioc_count);
}

static struct cfq_io_context *
cfq_cic_rb_lookup(struct cfq_data *cfqd, struct io_context *ioc)
{
      struct rb_node *n;
      struct cfq_io_context *cic;
      void *k, *key = cfqd;

restart:
      n = ioc->cic_root.rb_node;
      while (n) {
            cic = rb_entry(n, struct cfq_io_context, rb_node);
            /* ->key must be copied to avoid race with cfq_exit_queue() */
            k = cic->key;
            if (unlikely(!k)) {
                  cfq_drop_dead_cic(ioc, cic);
                  goto restart;
            }

            if (key < k)
                  n = n->rb_left;
            else if (key > k)
                  n = n->rb_right;
            else
                  return cic;
      }

      return NULL;
}

static inline void
cfq_cic_link(struct cfq_data *cfqd, struct io_context *ioc,
           struct cfq_io_context *cic)
{
      struct rb_node **p;
      struct rb_node *parent;
      struct cfq_io_context *__cic;
      void *k;

      cic->ioc = ioc;
      cic->key = cfqd;

      ioc->set_ioprio = cfq_ioc_set_ioprio;
restart:
      parent = NULL;
      p = &ioc->cic_root.rb_node;
      while (*p) {
            parent = *p;
            __cic = rb_entry(parent, struct cfq_io_context, rb_node);
            /* ->key must be copied to avoid race with cfq_exit_queue() */
            k = __cic->key;
            if (unlikely(!k)) {
                  cfq_drop_dead_cic(ioc, __cic);
                  goto restart;
            }

            if (cic->key < k)
                  p = &(*p)->rb_left;
            else if (cic->key > k)
                  p = &(*p)->rb_right;
            else
                  BUG();
      }

      spin_lock(&cfq_exit_lock);
      rb_link_node(&cic->rb_node, parent, p);
      rb_insert_color(&cic->rb_node, &ioc->cic_root);
      list_add(&cic->queue_list, &cfqd->cic_list);
      spin_unlock(&cfq_exit_lock);
}

/*
 * 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.
 */
static struct cfq_io_context *
cfq_get_io_context(struct cfq_data *cfqd, gfp_t 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;

      cic = cfq_cic_rb_lookup(cfqd, ioc);
      if (cic)
            goto out;

      cic = cfq_alloc_io_context(cfqd, gfp_mask);
      if (cic == NULL)
            goto err;

      cfq_cic_link(cfqd, ioc, 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;
}

static void
cfq_update_io_seektime(struct cfq_data *cfqd, struct cfq_io_context *cic,
                   struct cfq_rq *crq)
{
      sector_t sdist;
      u64 total;

      if (cic->last_request_pos < crq->request->sector)
            sdist = crq->request->sector - cic->last_request_pos;
      else
            sdist = cic->last_request_pos - crq->request->sector;

      /*
       * Don't allow the seek distance to get too large from the
       * odd fragment, pagein, etc
       */
      if (cic->seek_samples <= 60) /* second&third seek */
            sdist = min(sdist, (cic->seek_mean * 4) + 2*1024*1024);
      else
            sdist = min(sdist, (cic->seek_mean * 4)   + 2*1024*64);

      cic->seek_samples = (7*cic->seek_samples + 256) / 8;
      cic->seek_total = (7*cic->seek_total + (u64)256*sdist) / 8;
      total = cic->seek_total + (cic->seek_samples/2);
      do_div(total, cic->seek_samples);
      cic->seek_mean = (sector_t)total;
}

/*
 * 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 ||
          (cfqd->hw_tag && CIC_SEEKY(cic)))
            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 0;

      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, 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 = crq->io_context;

      /*
       * 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)) {
            /*
             * sync process issued an async request, if it's waiting
             * then expire it and kick rq handling.
             */
            if (cic == cfqd->active_cic &&
                del_timer(&cfqd->idle_slice_timer)) {
                  cfq_slice_expired(cfqd, 0);
                  cfq_start_queueing(cfqd, cfqq);
            }
            return;
      }

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

      cic->last_queue = jiffies;
      cic->last_request_pos = crq->request->sector + crq->request->nr_sectors;

      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);

      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 (sync)
            crq->io_context->last_end_request = now;

      /*
       * If this is the active queue, check if it needs to be expired,
       * or if we want to idle in case it has no pending requests.
       */
      if (cfqd->active_queue == cfqq) {
            if (time_after(now, cfqq->slice_end))
                  cfq_slice_expired(cfqd, 0);
            else if (sync && RB_EMPTY_ROOT(&cfqq->sort_list)) {
                  if (!cfq_arm_slice_timer(cfqd, cfqq))
                        cfq_schedule_dispatch(cfqd);
            }
      }
}

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 int
__cfq_may_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq,
            struct task_struct *task, int rw)
{
      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;
}

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;

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

            smp_mb();
            if (waitqueue_active(&rl->wait[READ]))
                  wake_up(&rl->wait[READ]);
            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,
            gfp_t 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;
      int is_sync = key != CFQ_KEY_ASYNC;

      might_sleep_if(gfp_mask & __GFP_WAIT);

      cic = cfq_get_io_context(cfqd, gfp_mask);

      spin_lock_irqsave(q->queue_lock, flags);

      if (!cic)
            goto queue_fail;

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

            cic->cfqq[is_sync] = cfqq;
      } else
            cfqq = cic->cfqq[is_sync];

      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_NODE(&crq->rb_node);
            crq->rb_key = 0;
            crq->request = rq;
            INIT_HLIST_NODE(&crq->hash);
            crq->cfq_queue = cfqq;
            crq->io_context = cic;

            if (is_sync)
                  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)
                  goto out_cont;

            /*
             * not expired and it has a request pending, let it dispatch
             */
            if (!RB_EMPTY_ROOT(&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))
            mod_timer(&cfqd->idle_class_timer, end);
      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_exit_queue(elevator_t *e)
{
      struct cfq_data *cfqd = e->elevator_data;
      request_queue_t *q = cfqd->queue;

      cfq_shutdown_timer_wq(cfqd);

      spin_lock(&cfq_exit_lock);
      spin_lock_irq(q->queue_lock);

      if (cfqd->active_queue)
            __cfq_slice_expired(cfqd, cfqd->active_queue, 0);

      while (!list_empty(&cfqd->cic_list)) {
            struct cfq_io_context *cic = list_entry(cfqd->cic_list.next,
                                          struct cfq_io_context,
                                          queue_list);
            if (cic->cfqq[ASYNC]) {
                  cfq_put_queue(cic->cfqq[ASYNC]);
                  cic->cfqq[ASYNC] = NULL;
            }
            if (cic->cfqq[SYNC]) {
                  cfq_put_queue(cic->cfqq[SYNC]);
                  cic->cfqq[SYNC] = NULL;
            }
            cic->key = NULL;
            list_del_init(&cic->queue_list);
      }

      spin_unlock_irq(q->queue_lock);
      spin_unlock(&cfq_exit_lock);

      cfq_shutdown_timer_wq(cfqd);

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

static void *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 NULL;

      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);
      INIT_LIST_HEAD(&cfqd->cic_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_slab_pool(BLKDEV_MIN_RQ, 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]);

      cfqd->queue = q;

      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);

      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;

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

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 -->
 */

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(elevator_t *e, char *page)                  \
{                                                     \
      struct cfq_data *cfqd = e->elevator_data;             \
      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_seek_max_show, cfqd->cfq_back_max, 0);
SHOW_FUNCTION(cfq_back_seek_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);
#undef SHOW_FUNCTION

#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)                 \
static ssize_t __FUNC(elevator_t *e, const char *page, size_t count)    \
{                                                     \
      struct cfq_data *cfqd = e->elevator_data;             \
      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_seek_max_store, &cfqd->cfq_back_max, 0, UINT_MAX, 0);
STORE_FUNCTION(cfq_back_seek_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);
#undef STORE_FUNCTION

#define CFQ_ATTR(name) \
      __ATTR(name, S_IRUGO|S_IWUSR, cfq_##name##_show, cfq_##name##_store)

static struct elv_fs_entry cfq_attrs[] = {
      CFQ_ATTR(quantum),
      CFQ_ATTR(queued),
      CFQ_ATTR(fifo_expire_sync),
      CFQ_ATTR(fifo_expire_async),
      CFQ_ATTR(back_seek_max),
      CFQ_ATTR(back_seek_penalty),
      CFQ_ATTR(slice_sync),
      CFQ_ATTR(slice_async),
      CFQ_ATTR(slice_async_rq),
      CFQ_ATTR(slice_idle),
      __ATTR_NULL
};

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,
            .trim =                       cfq_trim,
      },
      .elevator_attrs = cfq_attrs,
      .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)
{
      DECLARE_COMPLETION(all_gone);
      elv_unregister(&iosched_cfq);
      ioc_gone = &all_gone;
      /* ioc_gone's update must be visible before reading ioc_count */
      smp_wmb();
      if (atomic_read(&ioc_count))
            wait_for_completion(ioc_gone);
      synchronize_rcu();
      cfq_slab_kill();
}

module_init(cfq_init);
module_exit(cfq_exit);

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

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