/*

   *  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@kernel.dk>

   */

  #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_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)

  /*
   * 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)

  #define list_entry_cfqq(ptr)	list_entry((ptr), struct cfq_queue, cfq_list)

  #define RQ_CIC(rq)		((struct cfq_io_context*)(rq)->elevator_private)
  #define RQ_CFQQ(rq)		((rq)->elevator_private2)

  static struct kmem_cache *cfq_pool;
  static struct kmem_cache *cfq_ioc_pool;

  static DEFINE_PER_CPU(unsigned long, ioc_count);

  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_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;
  
  	/*

  	 * cfqq lookup hash
  	 */

  	struct hlist_head *cfq_hash;

  	int rq_in_driver;

  	int hw_tag;

  	/*

  	 * 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;

  	/*
  	 * tunables, see top of file
  	 */
  	unsigned int cfq_quantum;

  	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;

  	/* member of the rr/busy/cur/idle cfqd list */

  	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 request *next_rq;

  	/* requests queued in sort_list */
  	int queued[2];
  	/* currently allocated requests */
  	int allocated[2];

  	/* pending metadata requests */
  	int meta_pending;

  	/* fifo list of requests in sort_list */

  	struct list_head fifo;

  	unsigned long slice_end;

  	unsigned long service_last;

  	long slice_resid;

  	/* 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;

  };

  enum cfqq_state_flags {

  	CFQ_CFQQ_FLAG_on_rr = 0,	/* on round-robin busy list */
  	CFQ_CFQQ_FLAG_wait_request,	/* waiting for a request */
  	CFQ_CFQQ_FLAG_must_alloc,	/* must be allowed rq alloc */
  	CFQ_CFQQ_FLAG_must_alloc_slice,	/* per-slice must_alloc flag */
  	CFQ_CFQQ_FLAG_must_dispatch,	/* must dispatch, even if expired */
  	CFQ_CFQQ_FLAG_fifo_expire,	/* FIFO checked in this slice */
  	CFQ_CFQQ_FLAG_idle_window,	/* slice idling enabled */
  	CFQ_CFQQ_FLAG_prio_changed,	/* task priority has changed */
  	CFQ_CFQQ_FLAG_queue_new,	/* queue never been serviced */

  	CFQ_CFQQ_FLAG_slice_new,	/* no requests dispatched in slice */

  };
  
  #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(queue_new);

  CFQ_CFQQ_FNS(slice_new);

  #undef CFQ_CFQQ_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 request *);

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

  /*

   * 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, int is_sync)

  {

  	/*
  	 * Use the per-process queue, for read requests and syncronous writes
  	 */
  	if (!(rw & REQ_RW) || is_sync)

  		return task->pid;
  
  	return CFQ_KEY_ASYNC;
  }

  /*

   * 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;

  	cfqq->slice_end += cfqq->slice_resid;
  
  	/*
  	 * Don't carry over residual for more than one slice, we only want
  	 * to slightly correct the fairness. Carrying over forever would
  	 * easily introduce oscillations.
  	 */
  	cfqq->slice_resid = 0;

  }
  
  /*
   * We need to wrap this check in cfq_cfqq_slice_new(), since ->slice_end
   * isn't valid until the first request from the dispatch is activated
   * and the slice time set.
   */
  static inline int cfq_slice_used(struct cfq_queue *cfqq)
  {
  	if (cfq_cfqq_slice_new(cfqq))
  		return 0;
  	if (time_before(jiffies, cfqq->slice_end))
  		return 0;
  
  	return 1;
  }
  
  /*

   * Lifted from AS - choose which of rq1 and rq2 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 request *
  cfq_choose_req(struct cfq_data *cfqd, struct request *rq1, struct request *rq2)

  {
  	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 (rq1 == NULL || rq1 == rq2)
  		return rq2;
  	if (rq2 == NULL)
  		return rq1;

  	if (rq_is_sync(rq1) && !rq_is_sync(rq2))
  		return rq1;
  	else if (rq_is_sync(rq2) && !rq_is_sync(rq1))
  		return rq2;

  	if (rq_is_meta(rq1) && !rq_is_meta(rq2))
  		return rq1;
  	else if (rq_is_meta(rq2) && !rq_is_meta(rq1))
  		return rq2;

  	s1 = rq1->sector;
  	s2 = rq2->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: rq1 and rq2 not wrapped */

  		if (d1 < d2)

  			return rq1;

  		else if (d2 < d1)

  			return rq2;

  		else {
  			if (s1 >= s2)

  				return rq1;

  			else

  				return rq2;

  		}

  	case CFQ_RQ2_WRAP:

  		return rq1;

  	case CFQ_RQ1_WRAP:

  		return rq2;
  	case (CFQ_RQ1_WRAP|CFQ_RQ2_WRAP): /* both rqs wrapped */

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

  			return rq1;

  		else

  			return rq2;

  	}
  }
  
  /*
   * would be nice to take fifo expire time into account as well
   */

  static struct request *
  cfq_find_next_rq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
  		  struct request *last)

  {

  	struct rb_node *rbnext = rb_next(&last->rb_node);
  	struct rb_node *rbprev = rb_prev(&last->rb_node);

  	struct request *next = NULL, *prev = NULL;

  	BUG_ON(RB_EMPTY_NODE(&last->rb_node));

  
  	if (rbprev)

  		prev = rb_entry_rq(rbprev);

  	if (rbnext)

  		next = rb_entry_rq(rbnext);

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

  			next = rb_entry_rq(rbnext);

  	}

  	return cfq_choose_req(cfqd, next, prev);

  }

  static void cfq_resort_rr_list(struct cfq_queue *cfqq, int preempted)

  {

  	struct cfq_data *cfqd = cfqq->cfqd;

  	struct list_head *list, *n;
  	struct cfq_queue *__cfqq;

  	/*
  	 * Resorting requires the cfqq to be on the RR list already.
  	 */
  	if (!cfq_cfqq_on_rr(cfqq))
  		return;

  	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 (preempted || cfq_cfqq_queue_new(cfqq)) {

  		/*
  		 * If this queue was preempted or is new (never been serviced),
  		 * let it be added first for fairness but beind other new
  		 * queues.
  		 */
  		n = list;

  		while (n->next != list) {
  			__cfqq = list_entry_cfqq(n->next);
  			if (!cfq_cfqq_queue_new(__cfqq))
  				break;

  			n = n->next;
  		}

  		list_add_tail(&cfqq->cfq_list, n);
  	} else if (!cfq_cfqq_class_sync(cfqq)) {
  		/*
  		 * async queue always goes to the end. this wont be overly
  		 * unfair to writes, as the sort of the sync queue wont be
  		 * allowed to pass the async queue again.
  		 */
  		list_add_tail(&cfqq->cfq_list, list);
  	} else {
  		/*
  		 * sort by last service, but don't cross a new or async
  		 * queue. we don't cross a new queue because it hasn't been
  		 * service before, and we don't cross an async queue because
  		 * it gets added to the end on expire.
  		 */
  		n = list;
  		while ((n = n->prev) != list) {
  			struct cfq_queue *__cfqq = list_entry_cfqq(n);

  			if (!cfq_cfqq_class_sync(cfqq) || !__cfqq->service_last)
  				break;
  			if (time_before(__cfqq->service_last, cfqq->service_last))
  				break;
  		}
  		list_add(&cfqq->cfq_list, n);

  	}

  }
  
  /*
   * 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_del_init(&cfqq->cfq_list);

  
  	BUG_ON(!cfqd->busy_queues);
  	cfqd->busy_queues--;
  }
  
  /*
   * rb tree support functions
   */

  static inline void cfq_del_rq_rb(struct request *rq)

  {

  	struct cfq_queue *cfqq = RQ_CFQQ(rq);

  	struct cfq_data *cfqd = cfqq->cfqd;

  	const int sync = rq_is_sync(rq);

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

  	elv_rb_del(&cfqq->sort_list, rq);

  	if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list))

  		cfq_del_cfqq_rr(cfqd, cfqq);

  }

  static void cfq_add_rq_rb(struct request *rq)

  {

  	struct cfq_queue *cfqq = RQ_CFQQ(rq);

  	struct cfq_data *cfqd = cfqq->cfqd;

  	struct request *__alias;

  	cfqq->queued[rq_is_sync(rq)]++;

  
  	/*
  	 * looks a little odd, but the first insert might return an alias.
  	 * if that happens, put the alias on the dispatch list
  	 */

  	while ((__alias = elv_rb_add(&cfqq->sort_list, rq)) != NULL)

  		cfq_dispatch_insert(cfqd->queue, __alias);

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

  
  	/*
  	 * check if this request is a better next-serve candidate
  	 */
  	cfqq->next_rq = cfq_choose_req(cfqd, cfqq->next_rq, rq);
  	BUG_ON(!cfqq->next_rq);

  }
  
  static inline void

  cfq_reposition_rq_rb(struct cfq_queue *cfqq, struct request *rq)

  {

  	elv_rb_del(&cfqq->sort_list, rq);
  	cfqq->queued[rq_is_sync(rq)]--;

  	cfq_add_rq_rb(rq);

  }

  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), bio_sync(bio));

  	struct cfq_queue *cfqq;

  	cfqq = cfq_find_cfq_hash(cfqd, key, tsk->ioprio);

  	if (cfqq) {
  		sector_t sector = bio->bi_sector + bio_sectors(bio);

  		return elv_rb_find(&cfqq->sort_list, sector);

  	}

  	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_queue *cfqq = RQ_CFQQ(rq);

  	if (cfqq->next_rq == rq)
  		cfqq->next_rq = cfq_find_next_rq(cfqq->cfqd, cfqq, rq);

  	list_del_init(&rq->queuelist);

  	cfq_del_rq_rb(rq);

  
  	if (rq_is_meta(rq)) {
  		WARN_ON(!cfqq->meta_pending);
  		cfqq->meta_pending--;
  	}

  }
  
  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;

  	__rq = cfq_find_rq_fmerge(cfqd, bio);

  	if (__rq && elv_rq_merge_ok(__rq, bio)) {

  		*req = __rq;
  		return ELEVATOR_FRONT_MERGE;

  	}
  
  	return ELEVATOR_NO_MERGE;

  }

  static void cfq_merged_request(request_queue_t *q, struct request *req,
  			       int type)

  {

  	if (type == ELEVATOR_FRONT_MERGE) {

  		struct cfq_queue *cfqq = RQ_CFQQ(req);

  		cfq_reposition_rq_rb(cfqq, req);

  	}

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

  	/*
  	 * 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 int cfq_allow_merge(request_queue_t *q, struct request *rq,
  			   struct bio *bio)
  {
  	struct cfq_data *cfqd = q->elevator->elevator_data;
  	const int rw = bio_data_dir(bio);
  	struct cfq_queue *cfqq;
  	pid_t key;
  
  	/*

  	 * Disallow merge of a sync bio into an async request.

  	 */

  	if ((bio_data_dir(bio) == READ || bio_sync(bio)) && !rq_is_sync(rq))

  		return 0;
  
  	/*

  	 * Lookup the cfqq that this bio will be queued with. Allow
  	 * merge only if rq is queued there.

  	 */

  	key = cfq_queue_pid(current, rw, bio_sync(bio));

  	cfqq = cfq_find_cfq_hash(cfqd, key, current->ioprio);

  
  	if (cfqq == RQ_CFQQ(rq))
  		return 1;

  	return 0;

  }

  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_end = 0;

  		cfq_clear_cfqq_must_alloc_slice(cfqq);
  		cfq_clear_cfqq_fifo_expire(cfqq);

  		cfq_mark_cfqq_slice_new(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, int timed_out)

  {

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

  	cfq_clear_cfqq_must_dispatch(cfqq);
  	cfq_clear_cfqq_wait_request(cfqq);

  	cfq_clear_cfqq_queue_new(cfqq);

  
  	/*
  	 * store what was left of this slice, if the queue idled out
  	 * or was preempted
  	 */

  	if (timed_out && !cfq_cfqq_slice_new(cfqq))

  		cfqq->slice_resid = cfqq->slice_end - jiffies;

  	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,
  				     int timed_out)

  {
  	struct cfq_queue *cfqq = cfqd->active_queue;
  
  	if (cfqq)

  		__cfq_slice_expired(cfqd, cfqq, preempted, timed_out);

  }
  
  /*

   * 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 (!list_empty(&cfqd->cur_rr) || cfq_get_next_prio_level(cfqd) != -1) {
  		/*
  		 * 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
  		 */

  		cfqq = list_entry_cfqq(cfqd->cur_rr.next);

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

  		cfqq = list_entry_cfqq(cfqd->busy_rr.next);

  	} else if (!list_empty(&cfqd->idle_rr)) {
  		/*
  		 * 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
  		 */

  		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 = cfqd->active_queue;

  	struct cfq_io_context *cic;

  	unsigned long sl;

  	WARN_ON(!RB_EMPTY_ROOT(&cfqq->sort_list));

  
  	/*
  	 * 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 request *rq)

  {
  	struct cfq_data *cfqd = q->elevator->elevator_data;

  	struct cfq_queue *cfqq = RQ_CFQQ(rq);

  	cfq_remove_request(rq);
  	cfqq->on_dispatch[rq_is_sync(rq)]++;
  	elv_dispatch_sort(q, rq);

  
  	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 request *cfq_check_fifo(struct cfq_queue *cfqq)

  {
  	struct cfq_data *cfqd = cfqq->cfqd;

  	struct request *rq;

  	int fifo;

  	if (cfq_cfqq_fifo_expire(cfqq))

  		return NULL;

  
  	cfq_mark_cfqq_fifo_expire(cfqq);

  	if (list_empty(&cfqq->fifo))
  		return NULL;

  	fifo = cfq_cfqq_class_sync(cfqq);
  	rq = rq_entry_fifo(cfqq->fifo.next);

  	if (time_after(jiffies, rq->start_time + cfqd->cfq_fifo_expire[fifo]))

  		return rq;

  
  	return NULL;
  }

  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)

  {

  	struct cfq_queue *cfqq;

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

  	/*
  	 * slice has expired
  	 */

  	if (!cfq_cfqq_must_dispatch(cfqq) && cfq_slice_used(cfqq))

  		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_slice_new(cfqq) || cfq_cfqq_dispatched(cfqq)) {

  		cfqq = NULL;
  		goto keep_queue;
  	} else if (cfq_cfqq_class_sync(cfqq)) {

  		if (cfq_arm_slice_timer(cfqd))

  			return NULL;
  	}

  expire:

  	cfq_slice_expired(cfqd, 0, 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 request *rq;

  
  		/*

  		 * follow expired path, else get first next available

  		 */

  		if ((rq = cfq_check_fifo(cfqq)) == NULL)
  			rq = cfqq->next_rq;

  
  		/*
  		 * finally, insert request into driver dispatch list
  		 */

  		cfq_dispatch_insert(cfqd->queue, rq);

  		cfqd->dispatch_slice++;
  		dispatched++;

  		if (!cfqd->active_cic) {

  			atomic_inc(&RQ_CIC(rq)->ioc->refcount);
  			cfqd->active_cic = RQ_CIC(rq);

  		}

  		if (RB_EMPTY_ROOT(&cfqq->sort_list))

  			break;
  
  	} while (dispatched < max_dispatch);
  
  	/*

  	 * expire an async queue immediately if it has used up its slice. idle
  	 * queue always expire after 1 dispatch round.
  	 */

  	if (cfqd->busy_queues > 1 && ((!cfq_cfqq_sync(cfqq) &&

  	    cfqd->dispatch_slice >= cfq_prio_to_maxrq(cfqd, cfqq)) ||

  	    cfq_class_idle(cfqq))) {

  		cfqq->slice_end = jiffies + 1;

  		cfq_slice_expired(cfqd, 0, 0);

  	}

  
  	return dispatched;
  }
  
  static int

  cfq_forced_dispatch_cfqqs(struct list_head *list)
  {

  	struct cfq_queue *cfqq, *next;

  	int dispatched;

  	dispatched = 0;

  	list_for_each_entry_safe(cfqq, next, list, cfq_list) {

  		while (cfqq->next_rq) {
  			cfq_dispatch_insert(cfqq->cfqd->queue, cfqq->next_rq);

  			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, 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;

  		if (cfqd->busy_queues > 1) {
  			/*
  			 * Don't repeat dispatch from the previous queue.
  			 */
  			if (prev_cfqq == cfqq)
  				break;

  			/*
  			 * So we have dispatched before in this round, if the
  			 * next queue has idling enabled (must be sync), don't
  			 * allow it service until the previous have continued.
  			 */
  			if (cfqd->rq_in_driver && cfq_cfqq_idle_window(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);

  		prev_cfqq = cfqq;

  	}

  	return dispatched;

  }

  /*

   * task holds one reference to the queue, dropped when task exits. each rq
   * in-flight on this queue also holds a reference, dropped when rq is freed.

   *
   * 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, 0);

  		cfq_schedule_dispatch(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 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++;

  	}

  	elv_ioc_count_mod(ioc_count, -freed);
  
  	if (ioc_gone && !elv_ioc_count_read(ioc_count))

  		complete(ioc_gone);

  }

  static void cfq_exit_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq)

  {

  	if (unlikely(cfqq == cfqd->active_queue)) {

  		__cfq_slice_expired(cfqd, cfqq, 0, 0);

  		cfq_schedule_dispatch(cfqd);
  	}

  	cfq_put_queue(cfqq);
  }

  static void __cfq_exit_single_io_context(struct cfq_data *cfqd,
  					 struct cfq_io_context *cic)
  {

  	list_del_init(&cic->queue_list);
  	smp_wmb();
  	cic->key = NULL;

  	if (cic->cfqq[ASYNC]) {

  		cfq_exit_cfqq(cfqd, cic->cfqq[ASYNC]);

  		cic->cfqq[ASYNC] = NULL;
  	}
  
  	if (cic->cfqq[SYNC]) {

  		cfq_exit_cfqq(cfqd, cic->cfqq[SYNC]);

  		cic->cfqq[SYNC] = NULL;
  	}

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

  	if (cfqd) {
  		request_queue_t *q = cfqd->queue;

  		spin_lock_irq(q->queue_lock);

  		__cfq_exit_single_io_context(cfqd, cic);

  		spin_unlock_irq(q->queue_lock);

  	}

  }

  static void cfq_exit_io_context(struct io_context *ioc)

  {

  	struct cfq_io_context *__cic;

  	struct rb_node *n;

  	/*
  	 * put the reference this task is holding to the various queues
  	 */

  
  	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);

  	}

  }

  static struct cfq_io_context *

  cfq_alloc_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)

  {

  	struct cfq_io_context *cic;

  	cic = kmem_cache_alloc_node(cfq_ioc_pool, gfp_mask, cfqd->queue->node);

  	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;

  		elv_ioc_count_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
  ", 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;

  	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;

  	unsigned long flags;

  	if (unlikely(!cfqd))
  		return;

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

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

  }

  static void cfq_ioc_set_ioprio(struct io_context *ioc)

  {

  	struct cfq_io_context *cic;

  	struct rb_node *n;

  	ioc->ioprio_changed = 0;

  	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);
  	}

  }
  
  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) {

  			/*
  			 * Inform the allocator of the fact that we will
  			 * just repeat this allocation if it fails, to allow
  			 * the allocator to do whatever it needs to attempt to
  			 * free memory.
  			 */

  			spin_unlock_irq(cfqd->queue->queue_lock);

  			new_cfqq = kmem_cache_alloc_node(cfq_pool, gfp_mask|__GFP_NOFAIL, cfqd->queue->node);

  			spin_lock_irq(cfqd->queue->queue_lock);
  			goto retry;
  		} else {

  			cfqq = kmem_cache_alloc_node(cfq_pool, gfp_mask, cfqd->queue->node);

  			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;

  		if (key != CFQ_KEY_ASYNC)
  			cfq_mark_cfqq_idle_window(cfqq);

  		cfq_mark_cfqq_prio_changed(cfqq);

  		cfq_mark_cfqq_queue_new(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)
  {

  	WARN_ON(!list_empty(&cic->queue_list));

  	rb_erase(&cic->rb_node, &ioc->cic_root);

  	kmem_cache_free(cfq_ioc_pool, cic);

  	elv_ioc_count_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;

  	unsigned long flags;

  	void *k;

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

  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();
  	}
  
  	rb_link_node(&cic->rb_node, parent, p);
  	rb_insert_color(&cic->rb_node, &ioc->cic_root);

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

  	list_add(&cic->queue_list, &cfqd->cic_list);

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

  }

  /*
   * 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, cfqd->queue->node);

  	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:

  	smp_read_barrier_depends();
  	if (unlikely(ioc->ioprio_changed))
  		cfq_ioc_set_ioprio(ioc);

  	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 = jiffies - cic->last_end_request;
  	unsigned long 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_io_context *cic, struct request *rq)