/*

   *  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/slab.h>

  #include <linux/blkdev.h>
  #include <linux/elevator.h>

  #include <linux/jiffies.h>

  #include <linux/rbtree.h>

  #include <linux/ioprio.h>

  #include <linux/blktrace_api.h>

  #include "cfq.h"

  
  /*
   * tunables
   */

  /* max queue in one round of service */

  static const int cfq_quantum = 8;

  static const int cfq_fifo_expire[2] = { HZ / 4, HZ / 8 };

  /* maximum backwards seek, in KiB */
  static const int cfq_back_max = 16 * 1024;
  /* penalty of a backwards seek */
  static const int cfq_back_penalty = 2;

  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;

  static int cfq_group_idle = HZ / 125;

  static const int cfq_target_latency = HZ * 3/10; /* 300 ms */
  static const int cfq_hist_divisor = 4;

  /*

   * offset from end of service tree

   */

  #define CFQ_IDLE_DELAY		(HZ / 5)

  
  /*
   * below this threshold, we consider thinktime immediate
   */
  #define CFQ_MIN_TT		(2)

  #define CFQ_SLICE_SCALE		(5)

  #define CFQ_HW_QUEUE_MIN	(5)

  #define CFQ_SERVICE_SHIFT       12

  #define CFQQ_SEEK_THR		(sector_t)(8 * 100)

  #define CFQQ_CLOSE_THR		(sector_t)(8 * 1024)

  #define CFQQ_SECT_THR_NONROT	(sector_t)(2 * 32)

  #define CFQQ_SEEKY(cfqq)	(hweight32(cfqq->seek_history) > 32/8)

  #define RQ_CIC(rq)		\

  	((struct cfq_io_context *) (rq)->elevator_private[0])
  #define RQ_CFQQ(rq)		(struct cfq_queue *) ((rq)->elevator_private[1])
  #define RQ_CFQG(rq)		(struct cfq_group *) ((rq)->elevator_private[2])

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

  static DEFINE_PER_CPU(unsigned long, cfq_ioc_count);

  static struct completion *ioc_gone;

  static DEFINE_SPINLOCK(ioc_gone_lock);

  static DEFINE_SPINLOCK(cic_index_lock);
  static DEFINE_IDA(cic_index_ida);

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

  #define rb_entry_cfqg(node)	rb_entry((node), struct cfq_group, rb_node)

  /*

   * Most of our rbtree usage is for sorting with min extraction, so
   * if we cache the leftmost node we don't have to walk down the tree
   * to find it. Idea borrowed from Ingo Molnars CFS scheduler. We should
   * move this into the elevator for the rq sorting as well.
   */
  struct cfq_rb_root {
  	struct rb_root rb;
  	struct rb_node *left;

  	unsigned count;

  	unsigned total_weight;

  	u64 min_vdisktime;

  };

  #define CFQ_RB_ROOT	(struct cfq_rb_root) { .rb = RB_ROOT, .left = NULL, \
  			.count = 0, .min_vdisktime = 0, }

  
  /*

   * Per process-grouping structure
   */
  struct cfq_queue {
  	/* reference count */

  	int ref;

  	/* various state flags, see below */
  	unsigned int flags;
  	/* parent cfq_data */
  	struct cfq_data *cfqd;
  	/* service_tree member */
  	struct rb_node rb_node;
  	/* service_tree key */
  	unsigned long rb_key;
  	/* prio tree member */
  	struct rb_node p_node;
  	/* prio tree root we belong to, if any */
  	struct rb_root *p_root;
  	/* 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];
  	/* fifo list of requests in sort_list */
  	struct list_head fifo;

  	/* time when queue got scheduled in to dispatch first request. */
  	unsigned long dispatch_start;

  	unsigned int allocated_slice;

  	unsigned int slice_dispatch;

  	/* time when first request from queue completed and slice started. */
  	unsigned long slice_start;

  	unsigned long slice_end;
  	long slice_resid;

  
  	/* pending metadata requests */
  	int meta_pending;
  	/* number of requests that are on the dispatch list or inside driver */
  	int dispatched;
  
  	/* io prio of this group */
  	unsigned short ioprio, org_ioprio;
  	unsigned short ioprio_class, org_ioprio_class;

  	pid_t pid;

  	u32 seek_history;

  	sector_t last_request_pos;

  	struct cfq_rb_root *service_tree;

  	struct cfq_queue *new_cfqq;

  	struct cfq_group *cfqg;

  	/* Number of sectors dispatched from queue in single dispatch round */
  	unsigned long nr_sectors;

  };
  
  /*

   * First index in the service_trees.

   * IDLE is handled separately, so it has negative index
   */
  enum wl_prio_t {

  	BE_WORKLOAD = 0,

  	RT_WORKLOAD = 1,
  	IDLE_WORKLOAD = 2,

  	CFQ_PRIO_NR,

  };
  
  /*

   * Second index in the service_trees.
   */
  enum wl_type_t {
  	ASYNC_WORKLOAD = 0,
  	SYNC_NOIDLE_WORKLOAD = 1,
  	SYNC_WORKLOAD = 2
  };

  /* This is per cgroup per device grouping structure */
  struct cfq_group {

  	/* group service_tree member */
  	struct rb_node rb_node;
  
  	/* group service_tree key */
  	u64 vdisktime;

  	unsigned int weight;

  	unsigned int new_weight;
  	bool needs_update;

  
  	/* number of cfqq currently on this group */
  	int nr_cfqq;

  	/*

  	 * Per group busy queues average. Useful for workload slice calc. We

  	 * create the array for each prio class but at run time it is used
  	 * only for RT and BE class and slot for IDLE class remains unused.
  	 * This is primarily done to avoid confusion and a gcc warning.
  	 */
  	unsigned int busy_queues_avg[CFQ_PRIO_NR];
  	/*
  	 * rr lists of queues with requests. We maintain service trees for
  	 * RT and BE classes. These trees are subdivided in subclasses
  	 * of SYNC, SYNC_NOIDLE and ASYNC based on workload type. For IDLE
  	 * class there is no subclassification and all the cfq queues go on
  	 * a single tree service_tree_idle.

  	 * Counts are embedded in the cfq_rb_root
  	 */
  	struct cfq_rb_root service_trees[2][3];
  	struct cfq_rb_root service_tree_idle;

  
  	unsigned long saved_workload_slice;
  	enum wl_type_t saved_workload;
  	enum wl_prio_t saved_serving_prio;

  	struct blkio_group blkg;
  #ifdef CONFIG_CFQ_GROUP_IOSCHED
  	struct hlist_node cfqd_node;

  	int ref;

  #endif

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

  };

  
  /*

   * Per block device queue structure
   */

  struct cfq_data {

  	struct request_queue *queue;

  	/* Root service tree for cfq_groups */
  	struct cfq_rb_root grp_service_tree;

  	struct cfq_group root_group;

  
  	/*

  	 * The priority currently being served

  	 */

  	enum wl_prio_t serving_prio;

  	enum wl_type_t serving_type;
  	unsigned long workload_expires;

  	struct cfq_group *serving_group;

  
  	/*
  	 * Each priority tree is sorted by next_request position.  These
  	 * trees are used when determining if two or more queues are
  	 * interleaving requests (see cfq_close_cooperator).
  	 */
  	struct rb_root prio_trees[CFQ_PRIO_LISTS];

  	unsigned int busy_queues;

  	unsigned int busy_sync_queues;

  	int rq_in_driver;
  	int rq_in_flight[2];

  
  	/*
  	 * queue-depth detection
  	 */
  	int rq_queued;

  	int hw_tag;

  	/*
  	 * hw_tag can be
  	 * -1 => indeterminate, (cfq will behave as if NCQ is present, to allow better detection)
  	 *  1 => NCQ is present (hw_tag_est_depth is the estimated max depth)
  	 *  0 => no NCQ
  	 */
  	int hw_tag_est_depth;
  	unsigned int hw_tag_samples;

  	/*

  	 * 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;

  	/*
  	 * async queue for each priority case
  	 */
  	struct cfq_queue *async_cfqq[2][IOPRIO_BE_NR];
  	struct cfq_queue *async_idle_cfqq;

  	sector_t last_position;

  	/*
  	 * 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;

  	unsigned int cfq_group_idle;

  	unsigned int cfq_latency;

  	unsigned int cic_index;

  	struct list_head cic_list;

  	/*
  	 * Fallback dummy cfqq for extreme OOM conditions
  	 */
  	struct cfq_queue oom_cfqq;

  	unsigned long last_delayed_sync;

  
  	/* List of cfq groups being managed on this device*/
  	struct hlist_head cfqg_list;

  
  	/* Number of groups which are on blkcg->blkg_list */
  	unsigned int nr_blkcg_linked_grps;

  };

  static struct cfq_group *cfq_get_next_cfqg(struct cfq_data *cfqd);

  static struct cfq_rb_root *service_tree_for(struct cfq_group *cfqg,
  					    enum wl_prio_t prio,

  					    enum wl_type_t type)

  {

  	if (!cfqg)
  		return NULL;

  	if (prio == IDLE_WORKLOAD)

  		return &cfqg->service_tree_idle;

  	return &cfqg->service_trees[prio][type];

  }

  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_dispatch,	/* must be allowed a dispatch */

  	CFQ_CFQQ_FLAG_must_alloc_slice,	/* per-slice must_alloc flag */

  	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_slice_new,	/* no requests dispatched in slice */

  	CFQ_CFQQ_FLAG_sync,		/* synchronous queue */

  	CFQ_CFQQ_FLAG_coop,		/* cfqq is shared */

  	CFQ_CFQQ_FLAG_split_coop,	/* shared cfqq will be splitted */

  	CFQ_CFQQ_FLAG_deep,		/* sync cfqq experienced large depth */

  	CFQ_CFQQ_FLAG_wait_busy,	/* Waiting for next request */

  };
  
  #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_dispatch);

  CFQ_CFQQ_FNS(must_alloc_slice);

  CFQ_CFQQ_FNS(fifo_expire);
  CFQ_CFQQ_FNS(idle_window);
  CFQ_CFQQ_FNS(prio_changed);

  CFQ_CFQQ_FNS(slice_new);

  CFQ_CFQQ_FNS(sync);

  CFQ_CFQQ_FNS(coop);

  CFQ_CFQQ_FNS(split_coop);

  CFQ_CFQQ_FNS(deep);

  CFQ_CFQQ_FNS(wait_busy);

  #undef CFQ_CFQQ_FNS

  #ifdef CONFIG_CFQ_GROUP_IOSCHED

  #define cfq_log_cfqq(cfqd, cfqq, fmt, args...)	\
  	blk_add_trace_msg((cfqd)->queue, "cfq%d%c %s " fmt, (cfqq)->pid, \
  			cfq_cfqq_sync((cfqq)) ? 'S' : 'A', \

  			blkg_path(&(cfqq)->cfqg->blkg), ##args)

  
  #define cfq_log_cfqg(cfqd, cfqg, fmt, args...)				\
  	blk_add_trace_msg((cfqd)->queue, "%s " fmt,			\

  				blkg_path(&(cfqg)->blkg), ##args)       \

  
  #else

  #define cfq_log_cfqq(cfqd, cfqq, fmt, args...)	\
  	blk_add_trace_msg((cfqd)->queue, "cfq%d " fmt, (cfqq)->pid, ##args)

  #define cfq_log_cfqg(cfqd, cfqg, fmt, args...)		do {} while (0)

  #endif

  #define cfq_log(cfqd, fmt, args...)	\
  	blk_add_trace_msg((cfqd)->queue, "cfq " fmt, ##args)

  /* Traverses through cfq group service trees */
  #define for_each_cfqg_st(cfqg, i, j, st) \
  	for (i = 0; i <= IDLE_WORKLOAD; i++) \
  		for (j = 0, st = i < IDLE_WORKLOAD ? &cfqg->service_trees[i][j]\
  			: &cfqg->service_tree_idle; \
  			(i < IDLE_WORKLOAD && j <= SYNC_WORKLOAD) || \
  			(i == IDLE_WORKLOAD && j == 0); \
  			j++, st = i < IDLE_WORKLOAD ? \
  			&cfqg->service_trees[i][j]: NULL) \

  static inline bool iops_mode(struct cfq_data *cfqd)
  {
  	/*
  	 * If we are not idling on queues and it is a NCQ drive, parallel
  	 * execution of requests is on and measuring time is not possible
  	 * in most of the cases until and unless we drive shallower queue
  	 * depths and that becomes a performance bottleneck. In such cases
  	 * switch to start providing fairness in terms of number of IOs.
  	 */
  	if (!cfqd->cfq_slice_idle && cfqd->hw_tag)
  		return true;
  	else
  		return false;
  }

  static inline enum wl_prio_t cfqq_prio(struct cfq_queue *cfqq)
  {
  	if (cfq_class_idle(cfqq))
  		return IDLE_WORKLOAD;
  	if (cfq_class_rt(cfqq))
  		return RT_WORKLOAD;
  	return BE_WORKLOAD;
  }

  
  static enum wl_type_t cfqq_type(struct cfq_queue *cfqq)
  {
  	if (!cfq_cfqq_sync(cfqq))
  		return ASYNC_WORKLOAD;
  	if (!cfq_cfqq_idle_window(cfqq))
  		return SYNC_NOIDLE_WORKLOAD;
  	return SYNC_WORKLOAD;
  }

  static inline int cfq_group_busy_queues_wl(enum wl_prio_t wl,
  					struct cfq_data *cfqd,
  					struct cfq_group *cfqg)

  {
  	if (wl == IDLE_WORKLOAD)

  		return cfqg->service_tree_idle.count;

  	return cfqg->service_trees[wl][ASYNC_WORKLOAD].count
  		+ cfqg->service_trees[wl][SYNC_NOIDLE_WORKLOAD].count
  		+ cfqg->service_trees[wl][SYNC_WORKLOAD].count;

  }

  static inline int cfqg_busy_async_queues(struct cfq_data *cfqd,
  					struct cfq_group *cfqg)
  {
  	return cfqg->service_trees[RT_WORKLOAD][ASYNC_WORKLOAD].count
  		+ cfqg->service_trees[BE_WORKLOAD][ASYNC_WORKLOAD].count;
  }

  static void cfq_dispatch_insert(struct request_queue *, struct request *);

  static struct cfq_queue *cfq_get_queue(struct cfq_data *, bool,

  				       struct io_context *, gfp_t);

  static struct cfq_io_context *cfq_cic_lookup(struct cfq_data *,

  						struct io_context *);
  
  static inline struct cfq_queue *cic_to_cfqq(struct cfq_io_context *cic,

  					    bool is_sync)

  {

  	return cic->cfqq[is_sync];

  }
  
  static inline void cic_set_cfqq(struct cfq_io_context *cic,

  				struct cfq_queue *cfqq, bool is_sync)

  {

  	cic->cfqq[is_sync] = cfqq;

  }

  #define CIC_DEAD_KEY	1ul

  #define CIC_DEAD_INDEX_SHIFT	1

  
  static inline void *cfqd_dead_key(struct cfq_data *cfqd)
  {

  	return (void *)(cfqd->cic_index << CIC_DEAD_INDEX_SHIFT | CIC_DEAD_KEY);

  }
  
  static inline struct cfq_data *cic_to_cfqd(struct cfq_io_context *cic)
  {
  	struct cfq_data *cfqd = cic->key;
  
  	if (unlikely((unsigned long) cfqd & CIC_DEAD_KEY))
  		return NULL;
  
  	return cfqd;
  }

  /*
   * We regard a request as SYNC, if it's either a read or has the SYNC bit
   * set (in which case it could also be direct WRITE).
   */

  static inline bool cfq_bio_sync(struct bio *bio)

  {

  	return bio_data_dir(bio) == READ || (bio->bi_rw & REQ_SYNC);

  }

  /*

   * 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) {
  		cfq_log(cfqd, "schedule dispatch");

  		kblockd_schedule_work(cfqd->queue, &cfqd->unplug_work);

  	}

  }

  /*

   * 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_slice(struct cfq_data *cfqd, bool sync,

  				 unsigned short prio)

  {

  	const int base_slice = cfqd->cfq_slice[sync];

  	WARN_ON(prio >= IOPRIO_BE_NR);
  
  	return base_slice + (base_slice/CFQ_SLICE_SCALE * (4 - prio));
  }

  static inline int
  cfq_prio_to_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
  	return cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio);

  }

  static inline u64 cfq_scale_slice(unsigned long delta, struct cfq_group *cfqg)
  {
  	u64 d = delta << CFQ_SERVICE_SHIFT;
  
  	d = d * BLKIO_WEIGHT_DEFAULT;
  	do_div(d, cfqg->weight);
  	return d;
  }
  
  static inline u64 max_vdisktime(u64 min_vdisktime, u64 vdisktime)
  {
  	s64 delta = (s64)(vdisktime - min_vdisktime);
  	if (delta > 0)
  		min_vdisktime = vdisktime;
  
  	return min_vdisktime;
  }
  
  static inline u64 min_vdisktime(u64 min_vdisktime, u64 vdisktime)
  {
  	s64 delta = (s64)(vdisktime - min_vdisktime);
  	if (delta < 0)
  		min_vdisktime = vdisktime;
  
  	return min_vdisktime;
  }
  
  static void update_min_vdisktime(struct cfq_rb_root *st)
  {

  	struct cfq_group *cfqg;

  	if (st->left) {
  		cfqg = rb_entry_cfqg(st->left);

  		st->min_vdisktime = max_vdisktime(st->min_vdisktime,
  						  cfqg->vdisktime);

  	}

  }

  /*
   * get averaged number of queues of RT/BE priority.
   * average is updated, with a formula that gives more weight to higher numbers,
   * to quickly follows sudden increases and decrease slowly
   */

  static inline unsigned cfq_group_get_avg_queues(struct cfq_data *cfqd,
  					struct cfq_group *cfqg, bool rt)

  {

  	unsigned min_q, max_q;
  	unsigned mult  = cfq_hist_divisor - 1;
  	unsigned round = cfq_hist_divisor / 2;

  	unsigned busy = cfq_group_busy_queues_wl(rt, cfqd, cfqg);

  	min_q = min(cfqg->busy_queues_avg[rt], busy);
  	max_q = max(cfqg->busy_queues_avg[rt], busy);
  	cfqg->busy_queues_avg[rt] = (mult * max_q + min_q + round) /

  		cfq_hist_divisor;

  	return cfqg->busy_queues_avg[rt];
  }
  
  static inline unsigned
  cfq_group_slice(struct cfq_data *cfqd, struct cfq_group *cfqg)
  {
  	struct cfq_rb_root *st = &cfqd->grp_service_tree;
  
  	return cfq_target_latency * cfqg->weight / st->total_weight;

  }

  static inline unsigned

  cfq_scaled_cfqq_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)

  {

  	unsigned slice = cfq_prio_to_slice(cfqd, cfqq);
  	if (cfqd->cfq_latency) {

  		/*
  		 * interested queues (we consider only the ones with the same
  		 * priority class in the cfq group)
  		 */
  		unsigned iq = cfq_group_get_avg_queues(cfqd, cfqq->cfqg,
  						cfq_class_rt(cfqq));

  		unsigned sync_slice = cfqd->cfq_slice[1];
  		unsigned expect_latency = sync_slice * iq;

  		unsigned group_slice = cfq_group_slice(cfqd, cfqq->cfqg);
  
  		if (expect_latency > group_slice) {

  			unsigned base_low_slice = 2 * cfqd->cfq_slice_idle;
  			/* scale low_slice according to IO priority
  			 * and sync vs async */
  			unsigned low_slice =
  				min(slice, base_low_slice * slice / sync_slice);
  			/* the adapted slice value is scaled to fit all iqs
  			 * into the target latency */

  			slice = max(slice * group_slice / expect_latency,

  				    low_slice);
  		}
  	}

  	return slice;
  }
  
  static inline void
  cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {

  	unsigned slice = cfq_scaled_cfqq_slice(cfqd, cfqq);

  	cfqq->slice_start = jiffies;

  	cfqq->slice_end = jiffies + slice;

  	cfqq->allocated_slice = slice;

  	cfq_log_cfqq(cfqd, cfqq, "set_slice=%lu", cfqq->slice_end - jiffies);

  }
  
  /*
   * 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 bool cfq_slice_used(struct cfq_queue *cfqq)

  {
  	if (cfq_cfqq_slice_new(cfqq))

  		return false;

  	if (time_before(jiffies, cfqq->slice_end))

  		return false;

  	return true;

  }
  
  /*

   * 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)

  {

  	sector_t 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 rq_is_sync(rq1) ? rq1 : rq2;
  
  	if ((rq1->cmd_flags ^ rq2->cmd_flags) & REQ_META)
  		return rq1->cmd_flags & REQ_META ? rq1 : rq2;

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

  	/*
  	 * 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;

  	}
  }

  /*
   * The below is leftmost cache rbtree addon
   */

  static struct cfq_queue *cfq_rb_first(struct cfq_rb_root *root)

  {

  	/* Service tree is empty */
  	if (!root->count)
  		return NULL;

  	if (!root->left)
  		root->left = rb_first(&root->rb);

  	if (root->left)
  		return rb_entry(root->left, struct cfq_queue, rb_node);
  
  	return NULL;

  }

  static struct cfq_group *cfq_rb_first_group(struct cfq_rb_root *root)
  {
  	if (!root->left)
  		root->left = rb_first(&root->rb);
  
  	if (root->left)
  		return rb_entry_cfqg(root->left);
  
  	return NULL;
  }

  static void rb_erase_init(struct rb_node *n, struct rb_root *root)
  {
  	rb_erase(n, root);
  	RB_CLEAR_NODE(n);
  }

  static void cfq_rb_erase(struct rb_node *n, struct cfq_rb_root *root)
  {
  	if (root->left == n)
  		root->left = NULL;

  	rb_erase_init(n, &root->rb);

  	--root->count;

  }

  /*
   * 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, blk_rq_pos(last));

  }

  static unsigned long cfq_slice_offset(struct cfq_data *cfqd,
  				      struct cfq_queue *cfqq)

  {

  	/*
  	 * just an approximation, should be ok.
  	 */

  	return (cfqq->cfqg->nr_cfqq - 1) * (cfq_prio_slice(cfqd, 1, 0) -

  		       cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio));

  }

  static inline s64
  cfqg_key(struct cfq_rb_root *st, struct cfq_group *cfqg)
  {
  	return cfqg->vdisktime - st->min_vdisktime;
  }
  
  static void
  __cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg)
  {
  	struct rb_node **node = &st->rb.rb_node;
  	struct rb_node *parent = NULL;
  	struct cfq_group *__cfqg;
  	s64 key = cfqg_key(st, cfqg);
  	int left = 1;
  
  	while (*node != NULL) {
  		parent = *node;
  		__cfqg = rb_entry_cfqg(parent);
  
  		if (key < cfqg_key(st, __cfqg))
  			node = &parent->rb_left;
  		else {
  			node = &parent->rb_right;
  			left = 0;
  		}
  	}
  
  	if (left)
  		st->left = &cfqg->rb_node;
  
  	rb_link_node(&cfqg->rb_node, parent, node);
  	rb_insert_color(&cfqg->rb_node, &st->rb);
  }
  
  static void

  cfq_update_group_weight(struct cfq_group *cfqg)
  {
  	BUG_ON(!RB_EMPTY_NODE(&cfqg->rb_node));
  	if (cfqg->needs_update) {
  		cfqg->weight = cfqg->new_weight;
  		cfqg->needs_update = false;
  	}
  }
  
  static void
  cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg)
  {
  	BUG_ON(!RB_EMPTY_NODE(&cfqg->rb_node));
  
  	cfq_update_group_weight(cfqg);
  	__cfq_group_service_tree_add(st, cfqg);
  	st->total_weight += cfqg->weight;
  }
  
  static void
  cfq_group_notify_queue_add(struct cfq_data *cfqd, struct cfq_group *cfqg)

  {
  	struct cfq_rb_root *st = &cfqd->grp_service_tree;
  	struct cfq_group *__cfqg;
  	struct rb_node *n;
  
  	cfqg->nr_cfqq++;

  	if (!RB_EMPTY_NODE(&cfqg->rb_node))

  		return;
  
  	/*
  	 * Currently put the group at the end. Later implement something
  	 * so that groups get lesser vtime based on their weights, so that

  	 * if group does not loose all if it was not continuously backlogged.

  	 */
  	n = rb_last(&st->rb);
  	if (n) {
  		__cfqg = rb_entry_cfqg(n);
  		cfqg->vdisktime = __cfqg->vdisktime + CFQ_IDLE_DELAY;
  	} else
  		cfqg->vdisktime = st->min_vdisktime;

  	cfq_group_service_tree_add(st, cfqg);
  }

  static void
  cfq_group_service_tree_del(struct cfq_rb_root *st, struct cfq_group *cfqg)
  {
  	st->total_weight -= cfqg->weight;
  	if (!RB_EMPTY_NODE(&cfqg->rb_node))
  		cfq_rb_erase(&cfqg->rb_node, st);

  }
  
  static void

  cfq_group_notify_queue_del(struct cfq_data *cfqd, struct cfq_group *cfqg)

  {
  	struct cfq_rb_root *st = &cfqd->grp_service_tree;
  
  	BUG_ON(cfqg->nr_cfqq < 1);
  	cfqg->nr_cfqq--;

  	/* If there are other cfq queues under this group, don't delete it */
  	if (cfqg->nr_cfqq)
  		return;

  	cfq_log_cfqg(cfqd, cfqg, "del_from_rr group");

  	cfq_group_service_tree_del(st, cfqg);

  	cfqg->saved_workload_slice = 0;

  	cfq_blkiocg_update_dequeue_stats(&cfqg->blkg, 1);

  }

  static inline unsigned int cfq_cfqq_slice_usage(struct cfq_queue *cfqq,
  						unsigned int *unaccounted_time)

  {

  	unsigned int slice_used;

  
  	/*
  	 * Queue got expired before even a single request completed or
  	 * got expired immediately after first request completion.
  	 */
  	if (!cfqq->slice_start || cfqq->slice_start == jiffies) {
  		/*
  		 * Also charge the seek time incurred to the group, otherwise
  		 * if there are mutiple queues in the group, each can dispatch
  		 * a single request on seeky media and cause lots of seek time
  		 * and group will never know it.
  		 */
  		slice_used = max_t(unsigned, (jiffies - cfqq->dispatch_start),
  					1);
  	} else {
  		slice_used = jiffies - cfqq->slice_start;

  		if (slice_used > cfqq->allocated_slice) {
  			*unaccounted_time = slice_used - cfqq->allocated_slice;

  			slice_used = cfqq->allocated_slice;

  		}
  		if (time_after(cfqq->slice_start, cfqq->dispatch_start))
  			*unaccounted_time += cfqq->slice_start -
  					cfqq->dispatch_start;

  	}

  	return slice_used;
  }
  
  static void cfq_group_served(struct cfq_data *cfqd, struct cfq_group *cfqg,

  				struct cfq_queue *cfqq)

  {
  	struct cfq_rb_root *st = &cfqd->grp_service_tree;

  	unsigned int used_sl, charge, unaccounted_sl = 0;

  	int nr_sync = cfqg->nr_cfqq - cfqg_busy_async_queues(cfqd, cfqg)
  			- cfqg->service_tree_idle.count;
  
  	BUG_ON(nr_sync < 0);

  	used_sl = charge = cfq_cfqq_slice_usage(cfqq, &unaccounted_sl);

  	if (iops_mode(cfqd))
  		charge = cfqq->slice_dispatch;
  	else if (!cfq_cfqq_sync(cfqq) && !nr_sync)
  		charge = cfqq->allocated_slice;

  
  	/* Can't update vdisktime while group is on service tree */

  	cfq_group_service_tree_del(st, cfqg);

  	cfqg->vdisktime += cfq_scale_slice(charge, cfqg);

  	/* If a new weight was requested, update now, off tree */
  	cfq_group_service_tree_add(st, cfqg);

  
  	/* This group is being expired. Save the context */
  	if (time_after(cfqd->workload_expires, jiffies)) {
  		cfqg->saved_workload_slice = cfqd->workload_expires
  						- jiffies;
  		cfqg->saved_workload = cfqd->serving_type;
  		cfqg->saved_serving_prio = cfqd->serving_prio;
  	} else
  		cfqg->saved_workload_slice = 0;

  
  	cfq_log_cfqg(cfqd, cfqg, "served: vt=%llu min_vt=%llu", cfqg->vdisktime,
  					st->min_vdisktime);

  	cfq_log_cfqq(cfqq->cfqd, cfqq,
  		     "sl_used=%u disp=%u charge=%u iops=%u sect=%lu",
  		     used_sl, cfqq->slice_dispatch, charge,
  		     iops_mode(cfqd), cfqq->nr_sectors);

  	cfq_blkiocg_update_timeslice_used(&cfqg->blkg, used_sl,
  					  unaccounted_sl);

  	cfq_blkiocg_set_start_empty_time(&cfqg->blkg);

  }

  #ifdef CONFIG_CFQ_GROUP_IOSCHED
  static inline struct cfq_group *cfqg_of_blkg(struct blkio_group *blkg)
  {
  	if (blkg)
  		return container_of(blkg, struct cfq_group, blkg);
  	return NULL;
  }

  void cfq_update_blkio_group_weight(void *key, struct blkio_group *blkg,
  					unsigned int weight)

  {

  	struct cfq_group *cfqg = cfqg_of_blkg(blkg);
  	cfqg->new_weight = weight;
  	cfqg->needs_update = true;

  }

  static void cfq_init_add_cfqg_lists(struct cfq_data *cfqd,
  			struct cfq_group *cfqg, struct blkio_cgroup *blkcg)

  {

  	struct backing_dev_info *bdi = &cfqd->queue->backing_dev_info;
  	unsigned int major, minor;

  	/*
  	 * Add group onto cgroup list. It might happen that bdi->dev is
  	 * not initialized yet. Initialize this new group without major
  	 * and minor info and this info will be filled in once a new thread
  	 * comes for IO.
  	 */
  	if (bdi->dev) {

  		sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);

  		cfq_blkiocg_add_blkio_group(blkcg, &cfqg->blkg,
  					(void *)cfqd, MKDEV(major, minor));
  	} else
  		cfq_blkiocg_add_blkio_group(blkcg, &cfqg->blkg,
  					(void *)cfqd, 0);
  
  	cfqd->nr_blkcg_linked_grps++;
  	cfqg->weight = blkcg_get_weight(blkcg, cfqg->blkg.dev);
  
  	/* Add group on cfqd list */
  	hlist_add_head(&cfqg->cfqd_node, &cfqd->cfqg_list);
  }
  
  /*
   * Should be called from sleepable context. No request queue lock as per
   * cpu stats are allocated dynamically and alloc_percpu needs to be called
   * from sleepable context.
   */
  static struct cfq_group * cfq_alloc_cfqg(struct cfq_data *cfqd)
  {
  	struct cfq_group *cfqg = NULL;

  	int i, j, ret;

  	struct cfq_rb_root *st;

  
  	cfqg = kzalloc_node(sizeof(*cfqg), GFP_ATOMIC, cfqd->queue->node);
  	if (!cfqg)

  		return NULL;

  	for_each_cfqg_st(cfqg, i, j, st)
  		*st = CFQ_RB_ROOT;
  	RB_CLEAR_NODE(&cfqg->rb_node);

  	/*
  	 * Take the initial reference that will be released on destroy
  	 * This can be thought of a joint reference by cgroup and
  	 * elevator which will be dropped by either elevator exit
  	 * or cgroup deletion path depending on who is exiting first.
  	 */

  	cfqg->ref = 1;

  
  	ret = blkio_alloc_blkg_stats(&cfqg->blkg);
  	if (ret) {
  		kfree(cfqg);
  		return NULL;
  	}

  	return cfqg;
  }
  
  static struct cfq_group *
  cfq_find_cfqg(struct cfq_data *cfqd, struct blkio_cgroup *blkcg)
  {
  	struct cfq_group *cfqg = NULL;
  	void *key = cfqd;
  	struct backing_dev_info *bdi = &cfqd->queue->backing_dev_info;
  	unsigned int major, minor;

  	/*

  	 * This is the common case when there are no blkio cgroups.
  	 * Avoid lookup in this case

  	 */

  	if (blkcg == &blkio_root_cgroup)
  		cfqg = &cfqd->root_group;
  	else
  		cfqg = cfqg_of_blkg(blkiocg_lookup_group(blkcg, key));

  	if (cfqg && !cfqg->blkg.dev && bdi->dev && dev_name(bdi->dev)) {
  		sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
  		cfqg->blkg.dev = MKDEV(major, minor);
  	}

  	return cfqg;
  }
  
  /*

   * Search for the cfq group current task belongs to. request_queue lock must
   * be held.

   */

  static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd)

  {

  	struct blkio_cgroup *blkcg;

  	struct cfq_group *cfqg = NULL, *__cfqg = NULL;
  	struct request_queue *q = cfqd->queue;

  
  	rcu_read_lock();

  	blkcg = task_blkio_cgroup(current);

  	cfqg = cfq_find_cfqg(cfqd, blkcg);
  	if (cfqg) {
  		rcu_read_unlock();
  		return cfqg;
  	}
  
  	/*
  	 * Need to allocate a group. Allocation of group also needs allocation
  	 * of per cpu stats which in-turn takes a mutex() and can block. Hence
  	 * we need to drop rcu lock and queue_lock before we call alloc.
  	 *
  	 * Not taking any queue reference here and assuming that queue is
  	 * around by the time we return. CFQ queue allocation code does
  	 * the same. It might be racy though.
  	 */
  
  	rcu_read_unlock();
  	spin_unlock_irq(q->queue_lock);
  
  	cfqg = cfq_alloc_cfqg(cfqd);
  
  	spin_lock_irq(q->queue_lock);
  
  	rcu_read_lock();
  	blkcg = task_blkio_cgroup(current);
  
  	/*
  	 * If some other thread already allocated the group while we were
  	 * not holding queue lock, free up the group
  	 */
  	__cfqg = cfq_find_cfqg(cfqd, blkcg);
  
  	if (__cfqg) {
  		kfree(cfqg);
  		rcu_read_unlock();
  		return __cfqg;
  	}

  	if (!cfqg)

  		cfqg = &cfqd->root_group;

  
  	cfq_init_add_cfqg_lists(cfqd, cfqg, blkcg);

  	rcu_read_unlock();
  	return cfqg;
  }

  static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg)
  {

  	cfqg->ref++;

  	return cfqg;
  }

  static void cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg)
  {
  	/* Currently, all async queues are mapped to root group */
  	if (!cfq_cfqq_sync(cfqq))
  		cfqg = &cfqq->cfqd->root_group;
  
  	cfqq->cfqg = cfqg;

  	/* cfqq reference on cfqg */

  	cfqq->cfqg->ref++;

  }
  
  static void cfq_put_cfqg(struct cfq_group *cfqg)
  {
  	struct cfq_rb_root *st;
  	int i, j;

  	BUG_ON(cfqg->ref <= 0);
  	cfqg->ref--;
  	if (cfqg->ref)

  		return;
  	for_each_cfqg_st(cfqg, i, j, st)

  		BUG_ON(!RB_EMPTY_ROOT(&st->rb));

  	free_percpu(cfqg->blkg.stats_cpu);

  	kfree(cfqg);
  }
  
  static void cfq_destroy_cfqg(struct cfq_data *cfqd, struct cfq_group *cfqg)
  {
  	/* Something wrong if we are trying to remove same group twice */
  	BUG_ON(hlist_unhashed(&cfqg->cfqd_node));
  
  	hlist_del_init(&cfqg->cfqd_node);
  
  	/*
  	 * Put the reference taken at the time of creation so that when all
  	 * queues are gone, group can be destroyed.
  	 */
  	cfq_put_cfqg(cfqg);
  }
  
  static void cfq_release_cfq_groups(struct cfq_data *cfqd)
  {
  	struct hlist_node *pos, *n;
  	struct cfq_group *cfqg;
  
  	hlist_for_each_entry_safe(cfqg, pos, n, &cfqd->cfqg_list, cfqd_node) {
  		/*
  		 * If cgroup removal path got to blk_group first and removed
  		 * it from cgroup list, then it will take care of destroying
  		 * cfqg also.
  		 */

  		if (!cfq_blkiocg_del_blkio_group(&cfqg->blkg))

  			cfq_destroy_cfqg(cfqd, cfqg);
  	}

  }

  
  /*
   * Blk cgroup controller notification saying that blkio_group object is being
   * delinked as associated cgroup object is going away. That also means that
   * no new IO will come in this group. So get rid of this group as soon as
   * any pending IO in the group is finished.
   *
   * This function is called under rcu_read_lock(). key is the rcu protected
   * pointer. That means "key" is a valid cfq_data pointer as long as we are rcu
   * read lock.
   *
   * "key" was fetched from blkio_group under blkio_cgroup->lock. That means
   * it should not be NULL as even if elevator was exiting, cgroup deltion
   * path got to it first.
   */
  void cfq_unlink_blkio_group(void *key, struct blkio_group *blkg)
  {
  	unsigned long  flags;
  	struct cfq_data *cfqd = key;
  
  	spin_lock_irqsave(cfqd->queue->queue_lock, flags);
  	cfq_destroy_cfqg(cfqd, cfqg_of_blkg(blkg));
  	spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
  }

  #else /* GROUP_IOSCHED */

  static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd)

  {
  	return &cfqd->root_group;
  }

  
  static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg)
  {

  	return cfqg;

  }

  static inline void
  cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg) {
  	cfqq->cfqg = cfqg;
  }

  static void cfq_release_cfq_groups(struct cfq_data *cfqd) {}
  static inline void cfq_put_cfqg(struct cfq_group *cfqg) {}

  #endif /* GROUP_IOSCHED */

  /*

   * The cfqd->service_trees holds all pending cfq_queue's that have

   * requests waiting to be processed. It is sorted in the order that
   * we will service the queues.
   */

  static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,

  				 bool add_front)

  {

  	struct rb_node **p, *parent;
  	struct cfq_queue *__cfqq;

  	unsigned long rb_key;

  	struct cfq_rb_root *service_tree;

  	int left;

  	int new_cfqq = 1;

  	service_tree = service_tree_for(cfqq->cfqg, cfqq_prio(cfqq),

  						cfqq_type(cfqq));

  	if (cfq_class_idle(cfqq)) {
  		rb_key = CFQ_IDLE_DELAY;

  		parent = rb_last(&service_tree->rb);

  		if (parent && parent != &cfqq->rb_node) {
  			__cfqq = rb_entry(parent, struct cfq_queue, rb_node);
  			rb_key += __cfqq->rb_key;
  		} else
  			rb_key += jiffies;
  	} else if (!add_front) {

  		/*
  		 * Get our rb key offset. Subtract any residual slice
  		 * value carried from last service. A negative resid
  		 * count indicates slice overrun, and this should position
  		 * the next service time further away in the tree.
  		 */

  		rb_key = cfq_slice_offset(cfqd, cfqq) + jiffies;

  		rb_key -= cfqq->slice_resid;

  		cfqq->slice_resid = 0;

  	} else {
  		rb_key = -HZ;

  		__cfqq = cfq_rb_first(service_tree);

  		rb_key += __cfqq ? __cfqq->rb_key : jiffies;
  	}

  	if (!RB_EMPTY_NODE(&cfqq->rb_node)) {

  		new_cfqq = 0;

  		/*

  		 * same position, nothing more to do

  		 */

  		if (rb_key == cfqq->rb_key &&
  		    cfqq->service_tree == service_tree)

  			return;

  		cfq_rb_erase(&cfqq->rb_node, cfqq->service_tree);
  		cfqq->service_tree = NULL;

  	}

  	left = 1;

  	parent = NULL;

  	cfqq->service_tree = service_tree;
  	p = &service_tree->rb.rb_node;

  	while (*p) {

  		struct rb_node **n;

  		parent = *p;
  		__cfqq = rb_entry(parent, struct cfq_queue, rb_node);

  		/*

  		 * sort by key, that represents service time.

  		 */

  		if (time_before(rb_key, __cfqq->rb_key))

  			n = &(*p)->rb_left;

  		else {

  			n = &(*p)->rb_right;

  			left = 0;

  		}

  
  		p = n;

  	}

  	if (left)

  		service_tree->left = &cfqq->rb_node;

  	cfqq->rb_key = rb_key;
  	rb_link_node(&cfqq->rb_node, parent, p);

  	rb_insert_color(&cfqq->rb_node, &service_tree->rb);
  	service_tree->count++;

  	if (add_front || !new_cfqq)

  		return;

  	cfq_group_notify_queue_add(cfqd, cfqq->cfqg);

  }

  static struct cfq_queue *

  cfq_prio_tree_lookup(struct cfq_data *cfqd, struct rb_root *root,
  		     sector_t sector, struct rb_node **ret_parent,
  		     struct rb_node ***rb_link)

  {

  	struct rb_node **p, *parent;
  	struct cfq_queue *cfqq = NULL;
  
  	parent = NULL;
  	p = &root->rb_node;
  	while (*p) {
  		struct rb_node **n;
  
  		parent = *p;
  		cfqq = rb_entry(parent, struct cfq_queue, p_node);
  
  		/*
  		 * Sort strictly based on sector.  Smallest to the left,
  		 * largest to the right.
  		 */

  		if (sector > blk_rq_pos(cfqq->next_rq))

  			n = &(*p)->rb_right;

  		else if (sector < blk_rq_pos(cfqq->next_rq))

  			n = &(*p)->rb_left;
  		else
  			break;
  		p = n;

  		cfqq = NULL;

  	}
  
  	*ret_parent = parent;
  	if (rb_link)
  		*rb_link = p;

  	return cfqq;

  }
  
  static void cfq_prio_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {

  	struct rb_node **p, *parent;
  	struct cfq_queue *__cfqq;

  	if (cfqq->p_root) {
  		rb_erase(&cfqq->p_node, cfqq->p_root);
  		cfqq->p_root = NULL;
  	}

  
  	if (cfq_class_idle(cfqq))
  		return;
  	if (!cfqq->next_rq)
  		return;

  	cfqq->p_root = &cfqd->prio_trees[cfqq->org_ioprio];

  	__cfqq = cfq_prio_tree_lookup(cfqd, cfqq->p_root,
  				      blk_rq_pos(cfqq->next_rq), &parent, &p);

  	if (!__cfqq) {
  		rb_link_node(&cfqq->p_node, parent, p);

  		rb_insert_color(&cfqq->p_node, cfqq->p_root);
  	} else
  		cfqq->p_root = NULL;

  }

  /*
   * Update cfqq's position in the service tree.
   */

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

  {

  	/*
  	 * Resorting requires the cfqq to be on the RR list already.
  	 */

  	if (cfq_cfqq_on_rr(cfqq)) {

  		cfq_service_tree_add(cfqd, cfqq, 0);

  		cfq_prio_tree_add(cfqd, cfqq);
  	}

  }

  /*
   * add to busy list of queues for service, trying to be fair in ordering

   * the pending list according to last request service

   */

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

  {

  	cfq_log_cfqq(cfqd, cfqq, "add_to_rr");

  	BUG_ON(cfq_cfqq_on_rr(cfqq));
  	cfq_mark_cfqq_on_rr(cfqq);

  	cfqd->busy_queues++;

  	if (cfq_cfqq_sync(cfqq))
  		cfqd->busy_sync_queues++;

  	cfq_resort_rr_list(cfqd, cfqq);

  }

  /*
   * Called when the cfqq no longer has requests pending, remove it from
   * the service tree.
   */

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

  {

  	cfq_log_cfqq(cfqd, cfqq, "del_from_rr");

  	BUG_ON(!cfq_cfqq_on_rr(cfqq));
  	cfq_clear_cfqq_on_rr(cfqq);

  	if (!RB_EMPTY_NODE(&cfqq->rb_node)) {
  		cfq_rb_erase(&cfqq->rb_node, cfqq->service_tree);
  		cfqq->service_tree = NULL;
  	}

  	if (cfqq->p_root) {
  		rb_erase(&cfqq->p_node, cfqq->p_root);
  		cfqq->p_root = NULL;
  	}

  	cfq_group_notify_queue_del(cfqd, cfqq->cfqg);

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

  	if (cfq_cfqq_sync(cfqq))
  		cfqd->busy_sync_queues--;

  }
  
  /*
   * rb tree support functions
   */

  static void cfq_del_rq_rb(struct request *rq)

  {

  	struct cfq_queue *cfqq = RQ_CFQQ(rq);

  	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)) {
  		/*
  		 * Queue will be deleted from service tree when we actually
  		 * expire it later. Right now just remove it from prio tree
  		 * as it is empty.
  		 */
  		if (cfqq->p_root) {
  			rb_erase(&cfqq->p_node, cfqq->p_root);
  			cfqq->p_root = NULL;
  		}
  	}

  }

  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, *prev;

  	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
  	 */

  	prev = cfqq->next_rq;

  	cfqq->next_rq = cfq_choose_req(cfqd, cfqq->next_rq, rq, cfqd->last_position);

  
  	/*
  	 * adjust priority tree position, if ->next_rq changes
  	 */
  	if (prev != cfqq->next_rq)
  		cfq_prio_tree_add(cfqd, cfqq);

  	BUG_ON(!cfqq->next_rq);

  }

  static 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_blkiocg_update_io_remove_stats(&(RQ_CFQG(rq))->blkg,
  					rq_data_dir(rq), rq_is_sync(rq));

  	cfq_add_rq_rb(rq);

  	cfq_blkiocg_update_io_add_stats(&(RQ_CFQG(rq))->blkg,

  			&cfqq->cfqd->serving_group->blkg, rq_data_dir(rq),
  			rq_is_sync(rq));

  }

  static struct request *
  cfq_find_rq_fmerge(struct cfq_data *cfqd, struct bio *bio)

  {

  	struct task_struct *tsk = current;

  	struct cfq_io_context *cic;

  	struct cfq_queue *cfqq;

  	cic = cfq_cic_lookup(cfqd, tsk->io_context);

  	if (!cic)
  		return NULL;
  
  	cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));

  	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(struct request_queue *q, struct request *rq)

  {

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

  	cfqd->rq_in_driver++;

  	cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "activate rq, drv=%d",

  						cfqd->rq_in_driver);

  	cfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);

  }

  static void cfq_deactivate_request(struct request_queue *q, struct request *rq)

  {