/*
   * Interface for controlling IO bandwidth on a request queue
   *
   * Copyright (C) 2010 Vivek Goyal <vgoyal@redhat.com>
   */
  
  #include <linux/module.h>
  #include <linux/slab.h>
  #include <linux/blkdev.h>
  #include <linux/bio.h>
  #include <linux/blktrace_api.h>
  #include "blk-cgroup.h"
  
  /* Max dispatch from a group in 1 round */
  static int throtl_grp_quantum = 8;
  
  /* Total max dispatch from all groups in one round */
  static int throtl_quantum = 32;
  
  /* Throttling is performed over 100ms slice and after that slice is renewed */
  static unsigned long throtl_slice = HZ/10;	/* 100 ms */

  /* A workqueue to queue throttle related work */
  static struct workqueue_struct *kthrotld_workqueue;
  static void throtl_schedule_delayed_work(struct throtl_data *td,
  				unsigned long delay);

  struct throtl_rb_root {
  	struct rb_root rb;
  	struct rb_node *left;
  	unsigned int count;
  	unsigned long min_disptime;
  };
  
  #define THROTL_RB_ROOT	(struct throtl_rb_root) { .rb = RB_ROOT, .left = NULL, \
  			.count = 0, .min_disptime = 0}
  
  #define rb_entry_tg(node)	rb_entry((node), struct throtl_grp, rb_node)
  
  struct throtl_grp {
  	/* List of throtl groups on the request queue*/
  	struct hlist_node tg_node;
  
  	/* active throtl group service_tree member */
  	struct rb_node rb_node;
  
  	/*
  	 * Dispatch time in jiffies. This is the estimated time when group
  	 * will unthrottle and is ready to dispatch more bio. It is used as
  	 * key to sort active groups in service tree.
  	 */
  	unsigned long disptime;
  
  	struct blkio_group blkg;
  	atomic_t ref;
  	unsigned int flags;
  
  	/* Two lists for READ and WRITE */
  	struct bio_list bio_lists[2];
  
  	/* Number of queued bios on READ and WRITE lists */
  	unsigned int nr_queued[2];
  
  	/* bytes per second rate limits */
  	uint64_t bps[2];

  	/* IOPS limits */
  	unsigned int iops[2];

  	/* Number of bytes disptached in current slice */
  	uint64_t bytes_disp[2];

  	/* Number of bio's dispatched in current slice */
  	unsigned int io_disp[2];

  
  	/* When did we start a new slice */
  	unsigned long slice_start[2];
  	unsigned long slice_end[2];

  
  	/* Some throttle limits got updated for the group */

  	int limits_changed;

  };
  
  struct throtl_data
  {
  	/* List of throtl groups */
  	struct hlist_head tg_list;
  
  	/* service tree for active throtl groups */
  	struct throtl_rb_root tg_service_tree;
  
  	struct throtl_grp root_tg;
  	struct request_queue *queue;
  
  	/* Total Number of queued bios on READ and WRITE lists */
  	unsigned int nr_queued[2];
  
  	/*

  	 * number of total undestroyed groups

  	 */
  	unsigned int nr_undestroyed_grps;
  
  	/* Work for dispatching throttled bios */
  	struct delayed_work throtl_work;

  	int limits_changed;

  };
  
  enum tg_state_flags {
  	THROTL_TG_FLAG_on_rr = 0,	/* on round-robin busy list */
  };
  
  #define THROTL_TG_FNS(name)						\
  static inline void throtl_mark_tg_##name(struct throtl_grp *tg)		\
  {									\
  	(tg)->flags |= (1 << THROTL_TG_FLAG_##name);			\
  }									\
  static inline void throtl_clear_tg_##name(struct throtl_grp *tg)	\
  {									\
  	(tg)->flags &= ~(1 << THROTL_TG_FLAG_##name);			\
  }									\
  static inline int throtl_tg_##name(const struct throtl_grp *tg)		\
  {									\
  	return ((tg)->flags & (1 << THROTL_TG_FLAG_##name)) != 0;	\
  }
  
  THROTL_TG_FNS(on_rr);
  
  #define throtl_log_tg(td, tg, fmt, args...)				\
  	blk_add_trace_msg((td)->queue, "throtl %s " fmt,		\
  				blkg_path(&(tg)->blkg), ##args);      	\
  
  #define throtl_log(td, fmt, args...)	\
  	blk_add_trace_msg((td)->queue, "throtl " fmt, ##args)
  
  static inline struct throtl_grp *tg_of_blkg(struct blkio_group *blkg)
  {
  	if (blkg)
  		return container_of(blkg, struct throtl_grp, blkg);
  
  	return NULL;
  }
  
  static inline int total_nr_queued(struct throtl_data *td)
  {
  	return (td->nr_queued[0] + td->nr_queued[1]);
  }
  
  static inline struct throtl_grp *throtl_ref_get_tg(struct throtl_grp *tg)
  {
  	atomic_inc(&tg->ref);
  	return tg;
  }
  
  static void throtl_put_tg(struct throtl_grp *tg)
  {
  	BUG_ON(atomic_read(&tg->ref) <= 0);
  	if (!atomic_dec_and_test(&tg->ref))
  		return;
  	kfree(tg);
  }
  
  static struct throtl_grp * throtl_find_alloc_tg(struct throtl_data *td,
  			struct cgroup *cgroup)
  {
  	struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);
  	struct throtl_grp *tg = NULL;
  	void *key = td;
  	struct backing_dev_info *bdi = &td->queue->backing_dev_info;
  	unsigned int major, minor;
  
  	/*
  	 * TODO: Speed up blkiocg_lookup_group() by maintaining a radix
  	 * tree of blkg (instead of traversing through hash list all
  	 * the time.
  	 */

  
  	/*
  	 * This is the common case when there are no blkio cgroups.
   	 * Avoid lookup in this case
   	 */
  	if (blkcg == &blkio_root_cgroup)
  		tg = &td->root_tg;
  	else
  		tg = tg_of_blkg(blkiocg_lookup_group(blkcg, key));

  
  	/* Fill in device details for root group */
  	if (tg && !tg->blkg.dev && bdi->dev && dev_name(bdi->dev)) {
  		sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
  		tg->blkg.dev = MKDEV(major, minor);
  		goto done;
  	}
  
  	if (tg)
  		goto done;
  
  	tg = kzalloc_node(sizeof(*tg), GFP_ATOMIC, td->queue->node);
  	if (!tg)
  		goto done;
  
  	INIT_HLIST_NODE(&tg->tg_node);
  	RB_CLEAR_NODE(&tg->rb_node);
  	bio_list_init(&tg->bio_lists[0]);
  	bio_list_init(&tg->bio_lists[1]);

  	td->limits_changed = false;

  
  	/*
  	 * Take the initial reference that will be released on destroy
  	 * This can be thought of a joint reference by cgroup and
  	 * request queue which will be dropped by either request queue
  	 * exit or cgroup deletion path depending on who is exiting first.
  	 */
  	atomic_set(&tg->ref, 1);
  
  	/* Add group onto cgroup list */
  	sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
  	blkiocg_add_blkio_group(blkcg, &tg->blkg, (void *)td,
  				MKDEV(major, minor), BLKIO_POLICY_THROTL);
  
  	tg->bps[READ] = blkcg_get_read_bps(blkcg, tg->blkg.dev);
  	tg->bps[WRITE] = blkcg_get_write_bps(blkcg, tg->blkg.dev);

  	tg->iops[READ] = blkcg_get_read_iops(blkcg, tg->blkg.dev);
  	tg->iops[WRITE] = blkcg_get_write_iops(blkcg, tg->blkg.dev);

  
  	hlist_add_head(&tg->tg_node, &td->tg_list);
  	td->nr_undestroyed_grps++;
  done:
  	return tg;
  }
  
  static struct throtl_grp * throtl_get_tg(struct throtl_data *td)
  {
  	struct cgroup *cgroup;
  	struct throtl_grp *tg = NULL;
  
  	rcu_read_lock();
  	cgroup = task_cgroup(current, blkio_subsys_id);
  	tg = throtl_find_alloc_tg(td, cgroup);
  	if (!tg)
  		tg = &td->root_tg;
  	rcu_read_unlock();
  	return tg;
  }
  
  static struct throtl_grp *throtl_rb_first(struct throtl_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_tg(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 throtl_rb_erase(struct rb_node *n, struct throtl_rb_root *root)
  {
  	if (root->left == n)
  		root->left = NULL;
  	rb_erase_init(n, &root->rb);
  	--root->count;
  }
  
  static void update_min_dispatch_time(struct throtl_rb_root *st)
  {
  	struct throtl_grp *tg;
  
  	tg = throtl_rb_first(st);
  	if (!tg)
  		return;
  
  	st->min_disptime = tg->disptime;
  }
  
  static void
  tg_service_tree_add(struct throtl_rb_root *st, struct throtl_grp *tg)
  {
  	struct rb_node **node = &st->rb.rb_node;
  	struct rb_node *parent = NULL;
  	struct throtl_grp *__tg;
  	unsigned long key = tg->disptime;
  	int left = 1;
  
  	while (*node != NULL) {
  		parent = *node;
  		__tg = rb_entry_tg(parent);
  
  		if (time_before(key, __tg->disptime))
  			node = &parent->rb_left;
  		else {
  			node = &parent->rb_right;
  			left = 0;
  		}
  	}
  
  	if (left)
  		st->left = &tg->rb_node;
  
  	rb_link_node(&tg->rb_node, parent, node);
  	rb_insert_color(&tg->rb_node, &st->rb);
  }
  
  static void __throtl_enqueue_tg(struct throtl_data *td, struct throtl_grp *tg)
  {
  	struct throtl_rb_root *st = &td->tg_service_tree;
  
  	tg_service_tree_add(st, tg);
  	throtl_mark_tg_on_rr(tg);
  	st->count++;
  }
  
  static void throtl_enqueue_tg(struct throtl_data *td, struct throtl_grp *tg)
  {
  	if (!throtl_tg_on_rr(tg))
  		__throtl_enqueue_tg(td, tg);
  }
  
  static void __throtl_dequeue_tg(struct throtl_data *td, struct throtl_grp *tg)
  {
  	throtl_rb_erase(&tg->rb_node, &td->tg_service_tree);
  	throtl_clear_tg_on_rr(tg);
  }
  
  static void throtl_dequeue_tg(struct throtl_data *td, struct throtl_grp *tg)
  {
  	if (throtl_tg_on_rr(tg))
  		__throtl_dequeue_tg(td, tg);
  }
  
  static void throtl_schedule_next_dispatch(struct throtl_data *td)
  {
  	struct throtl_rb_root *st = &td->tg_service_tree;
  
  	/*
  	 * If there are more bios pending, schedule more work.
  	 */
  	if (!total_nr_queued(td))
  		return;
  
  	BUG_ON(!st->count);
  
  	update_min_dispatch_time(st);
  
  	if (time_before_eq(st->min_disptime, jiffies))

  		throtl_schedule_delayed_work(td, 0);

  	else

  		throtl_schedule_delayed_work(td, (st->min_disptime - jiffies));

  }
  
  static inline void
  throtl_start_new_slice(struct throtl_data *td, struct throtl_grp *tg, bool rw)
  {
  	tg->bytes_disp[rw] = 0;

  	tg->io_disp[rw] = 0;

  	tg->slice_start[rw] = jiffies;
  	tg->slice_end[rw] = jiffies + throtl_slice;
  	throtl_log_tg(td, tg, "[%c] new slice start=%lu end=%lu jiffies=%lu",
  			rw == READ ? 'R' : 'W', tg->slice_start[rw],
  			tg->slice_end[rw], jiffies);
  }

  static inline void throtl_set_slice_end(struct throtl_data *td,
  		struct throtl_grp *tg, bool rw, unsigned long jiffy_end)
  {
  	tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
  }

  static inline void throtl_extend_slice(struct throtl_data *td,
  		struct throtl_grp *tg, bool rw, unsigned long jiffy_end)
  {
  	tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
  	throtl_log_tg(td, tg, "[%c] extend slice start=%lu end=%lu jiffies=%lu",
  			rw == READ ? 'R' : 'W', tg->slice_start[rw],
  			tg->slice_end[rw], jiffies);
  }
  
  /* Determine if previously allocated or extended slice is complete or not */
  static bool
  throtl_slice_used(struct throtl_data *td, struct throtl_grp *tg, bool rw)
  {
  	if (time_in_range(jiffies, tg->slice_start[rw], tg->slice_end[rw]))
  		return 0;
  
  	return 1;
  }
  
  /* Trim the used slices and adjust slice start accordingly */
  static inline void
  throtl_trim_slice(struct throtl_data *td, struct throtl_grp *tg, bool rw)
  {

  	unsigned long nr_slices, time_elapsed, io_trim;
  	u64 bytes_trim, tmp;

  
  	BUG_ON(time_before(tg->slice_end[rw], tg->slice_start[rw]));
  
  	/*
  	 * If bps are unlimited (-1), then time slice don't get
  	 * renewed. Don't try to trim the slice if slice is used. A new
  	 * slice will start when appropriate.
  	 */
  	if (throtl_slice_used(td, tg, rw))
  		return;

  	/*
  	 * A bio has been dispatched. Also adjust slice_end. It might happen
  	 * that initially cgroup limit was very low resulting in high
  	 * slice_end, but later limit was bumped up and bio was dispached
  	 * sooner, then we need to reduce slice_end. A high bogus slice_end
  	 * is bad because it does not allow new slice to start.
  	 */
  
  	throtl_set_slice_end(td, tg, rw, jiffies + throtl_slice);

  	time_elapsed = jiffies - tg->slice_start[rw];
  
  	nr_slices = time_elapsed / throtl_slice;
  
  	if (!nr_slices)
  		return;

  	tmp = tg->bps[rw] * throtl_slice * nr_slices;
  	do_div(tmp, HZ);
  	bytes_trim = tmp;

  	io_trim = (tg->iops[rw] * throtl_slice * nr_slices)/HZ;

  	if (!bytes_trim && !io_trim)

  		return;
  
  	if (tg->bytes_disp[rw] >= bytes_trim)
  		tg->bytes_disp[rw] -= bytes_trim;
  	else
  		tg->bytes_disp[rw] = 0;

  	if (tg->io_disp[rw] >= io_trim)
  		tg->io_disp[rw] -= io_trim;
  	else
  		tg->io_disp[rw] = 0;

  	tg->slice_start[rw] += nr_slices * throtl_slice;

  	throtl_log_tg(td, tg, "[%c] trim slice nr=%lu bytes=%llu io=%lu"

  			" start=%lu end=%lu jiffies=%lu",

  			rw == READ ? 'R' : 'W', nr_slices, bytes_trim, io_trim,

  			tg->slice_start[rw], tg->slice_end[rw], jiffies);
  }

  static bool tg_with_in_iops_limit(struct throtl_data *td, struct throtl_grp *tg,
  		struct bio *bio, unsigned long *wait)

  {
  	bool rw = bio_data_dir(bio);

  	unsigned int io_allowed;

  	unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;

  	u64 tmp;

  	jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];

  	/* Slice has just started. Consider one slice interval */
  	if (!jiffy_elapsed)
  		jiffy_elapsed_rnd = throtl_slice;
  
  	jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);

  	/*
  	 * jiffy_elapsed_rnd should not be a big value as minimum iops can be
  	 * 1 then at max jiffy elapsed should be equivalent of 1 second as we
  	 * will allow dispatch after 1 second and after that slice should
  	 * have been trimmed.
  	 */
  
  	tmp = (u64)tg->iops[rw] * jiffy_elapsed_rnd;
  	do_div(tmp, HZ);
  
  	if (tmp > UINT_MAX)
  		io_allowed = UINT_MAX;
  	else
  		io_allowed = tmp;

  
  	if (tg->io_disp[rw] + 1 <= io_allowed) {

  		if (wait)
  			*wait = 0;
  		return 1;
  	}

  	/* Calc approx time to dispatch */
  	jiffy_wait = ((tg->io_disp[rw] + 1) * HZ)/tg->iops[rw] + 1;
  
  	if (jiffy_wait > jiffy_elapsed)
  		jiffy_wait = jiffy_wait - jiffy_elapsed;
  	else
  		jiffy_wait = 1;
  
  	if (wait)
  		*wait = jiffy_wait;
  	return 0;
  }
  
  static bool tg_with_in_bps_limit(struct throtl_data *td, struct throtl_grp *tg,
  		struct bio *bio, unsigned long *wait)
  {
  	bool rw = bio_data_dir(bio);

  	u64 bytes_allowed, extra_bytes, tmp;

  	unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;

  
  	jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
  
  	/* Slice has just started. Consider one slice interval */
  	if (!jiffy_elapsed)
  		jiffy_elapsed_rnd = throtl_slice;
  
  	jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);

  	tmp = tg->bps[rw] * jiffy_elapsed_rnd;
  	do_div(tmp, HZ);

  	bytes_allowed = tmp;

  
  	if (tg->bytes_disp[rw] + bio->bi_size <= bytes_allowed) {
  		if (wait)
  			*wait = 0;
  		return 1;
  	}
  
  	/* Calc approx time to dispatch */
  	extra_bytes = tg->bytes_disp[rw] + bio->bi_size - bytes_allowed;
  	jiffy_wait = div64_u64(extra_bytes * HZ, tg->bps[rw]);
  
  	if (!jiffy_wait)
  		jiffy_wait = 1;
  
  	/*
  	 * This wait time is without taking into consideration the rounding
  	 * up we did. Add that time also.
  	 */
  	jiffy_wait = jiffy_wait + (jiffy_elapsed_rnd - jiffy_elapsed);

  	if (wait)
  		*wait = jiffy_wait;

  	return 0;
  }
  
  /*
   * Returns whether one can dispatch a bio or not. Also returns approx number
   * of jiffies to wait before this bio is with-in IO rate and can be dispatched
   */
  static bool tg_may_dispatch(struct throtl_data *td, struct throtl_grp *tg,
  				struct bio *bio, unsigned long *wait)
  {
  	bool rw = bio_data_dir(bio);
  	unsigned long bps_wait = 0, iops_wait = 0, max_wait = 0;
  
  	/*
   	 * Currently whole state machine of group depends on first bio
  	 * queued in the group bio list. So one should not be calling
  	 * this function with a different bio if there are other bios
  	 * queued.
  	 */
  	BUG_ON(tg->nr_queued[rw] && bio != bio_list_peek(&tg->bio_lists[rw]));

  	/* If tg->bps = -1, then BW is unlimited */
  	if (tg->bps[rw] == -1 && tg->iops[rw] == -1) {
  		if (wait)
  			*wait = 0;
  		return 1;
  	}
  
  	/*
  	 * If previous slice expired, start a new one otherwise renew/extend
  	 * existing slice to make sure it is at least throtl_slice interval
  	 * long since now.
  	 */
  	if (throtl_slice_used(td, tg, rw))
  		throtl_start_new_slice(td, tg, rw);
  	else {
  		if (time_before(tg->slice_end[rw], jiffies + throtl_slice))
  			throtl_extend_slice(td, tg, rw, jiffies + throtl_slice);
  	}
  
  	if (tg_with_in_bps_limit(td, tg, bio, &bps_wait)
  	    && tg_with_in_iops_limit(td, tg, bio, &iops_wait)) {
  		if (wait)
  			*wait = 0;
  		return 1;
  	}
  
  	max_wait = max(bps_wait, iops_wait);
  
  	if (wait)
  		*wait = max_wait;
  
  	if (time_before(tg->slice_end[rw], jiffies + max_wait))
  		throtl_extend_slice(td, tg, rw, jiffies + max_wait);

  
  	return 0;
  }
  
  static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio)
  {
  	bool rw = bio_data_dir(bio);
  	bool sync = bio->bi_rw & REQ_SYNC;
  
  	/* Charge the bio to the group */
  	tg->bytes_disp[rw] += bio->bi_size;

  	tg->io_disp[rw]++;

  
  	/*
  	 * TODO: This will take blkg->stats_lock. Figure out a way
  	 * to avoid this cost.
  	 */
  	blkiocg_update_dispatch_stats(&tg->blkg, bio->bi_size, rw, sync);

  }
  
  static void throtl_add_bio_tg(struct throtl_data *td, struct throtl_grp *tg,
  			struct bio *bio)
  {
  	bool rw = bio_data_dir(bio);
  
  	bio_list_add(&tg->bio_lists[rw], bio);
  	/* Take a bio reference on tg */
  	throtl_ref_get_tg(tg);
  	tg->nr_queued[rw]++;
  	td->nr_queued[rw]++;
  	throtl_enqueue_tg(td, tg);
  }
  
  static void tg_update_disptime(struct throtl_data *td, struct throtl_grp *tg)
  {
  	unsigned long read_wait = -1, write_wait = -1, min_wait = -1, disptime;
  	struct bio *bio;
  
  	if ((bio = bio_list_peek(&tg->bio_lists[READ])))
  		tg_may_dispatch(td, tg, bio, &read_wait);
  
  	if ((bio = bio_list_peek(&tg->bio_lists[WRITE])))
  		tg_may_dispatch(td, tg, bio, &write_wait);
  
  	min_wait = min(read_wait, write_wait);
  	disptime = jiffies + min_wait;

  	/* Update dispatch time */
  	throtl_dequeue_tg(td, tg);
  	tg->disptime = disptime;
  	throtl_enqueue_tg(td, tg);
  }
  
  static void tg_dispatch_one_bio(struct throtl_data *td, struct throtl_grp *tg,
  				bool rw, struct bio_list *bl)
  {
  	struct bio *bio;
  
  	bio = bio_list_pop(&tg->bio_lists[rw]);
  	tg->nr_queued[rw]--;
  	/* Drop bio reference on tg */
  	throtl_put_tg(tg);
  
  	BUG_ON(td->nr_queued[rw] <= 0);
  	td->nr_queued[rw]--;
  
  	throtl_charge_bio(tg, bio);
  	bio_list_add(bl, bio);
  	bio->bi_rw |= REQ_THROTTLED;
  
  	throtl_trim_slice(td, tg, rw);
  }
  
  static int throtl_dispatch_tg(struct throtl_data *td, struct throtl_grp *tg,
  				struct bio_list *bl)
  {
  	unsigned int nr_reads = 0, nr_writes = 0;
  	unsigned int max_nr_reads = throtl_grp_quantum*3/4;

  	unsigned int max_nr_writes = throtl_grp_quantum - max_nr_reads;

  	struct bio *bio;
  
  	/* Try to dispatch 75% READS and 25% WRITES */
  
  	while ((bio = bio_list_peek(&tg->bio_lists[READ]))
  		&& tg_may_dispatch(td, tg, bio, NULL)) {
  
  		tg_dispatch_one_bio(td, tg, bio_data_dir(bio), bl);
  		nr_reads++;
  
  		if (nr_reads >= max_nr_reads)
  			break;
  	}
  
  	while ((bio = bio_list_peek(&tg->bio_lists[WRITE]))
  		&& tg_may_dispatch(td, tg, bio, NULL)) {
  
  		tg_dispatch_one_bio(td, tg, bio_data_dir(bio), bl);
  		nr_writes++;
  
  		if (nr_writes >= max_nr_writes)
  			break;
  	}
  
  	return nr_reads + nr_writes;
  }
  
  static int throtl_select_dispatch(struct throtl_data *td, struct bio_list *bl)
  {
  	unsigned int nr_disp = 0;
  	struct throtl_grp *tg;
  	struct throtl_rb_root *st = &td->tg_service_tree;
  
  	while (1) {
  		tg = throtl_rb_first(st);
  
  		if (!tg)
  			break;
  
  		if (time_before(jiffies, tg->disptime))
  			break;
  
  		throtl_dequeue_tg(td, tg);
  
  		nr_disp += throtl_dispatch_tg(td, tg, bl);
  
  		if (tg->nr_queued[0] || tg->nr_queued[1]) {
  			tg_update_disptime(td, tg);
  			throtl_enqueue_tg(td, tg);
  		}
  
  		if (nr_disp >= throtl_quantum)
  			break;
  	}
  
  	return nr_disp;
  }

  static void throtl_process_limit_change(struct throtl_data *td)
  {
  	struct throtl_grp *tg;
  	struct hlist_node *pos, *n;

  	if (!td->limits_changed)

  		return;

  	xchg(&td->limits_changed, false);

  	throtl_log(td, "limits changed");

  	hlist_for_each_entry_safe(tg, pos, n, &td->tg_list, tg_node) {

  		if (!tg->limits_changed)
  			continue;
  
  		if (!xchg(&tg->limits_changed, false))
  			continue;
  
  		throtl_log_tg(td, tg, "limit change rbps=%llu wbps=%llu"
  			" riops=%u wiops=%u", tg->bps[READ], tg->bps[WRITE],
  			tg->iops[READ], tg->iops[WRITE]);

  		/*
  		 * Restart the slices for both READ and WRITES. It
  		 * might happen that a group's limit are dropped
  		 * suddenly and we don't want to account recently
  		 * dispatched IO with new low rate
  		 */
  		throtl_start_new_slice(td, tg, 0);
  		throtl_start_new_slice(td, tg, 1);

  		if (throtl_tg_on_rr(tg))

  			tg_update_disptime(td, tg);

  	}

  }

  /* Dispatch throttled bios. Should be called without queue lock held. */
  static int throtl_dispatch(struct request_queue *q)
  {
  	struct throtl_data *td = q->td;
  	unsigned int nr_disp = 0;
  	struct bio_list bio_list_on_stack;
  	struct bio *bio;

  	struct blk_plug plug;

  
  	spin_lock_irq(q->queue_lock);

  	throtl_process_limit_change(td);

  	if (!total_nr_queued(td))
  		goto out;
  
  	bio_list_init(&bio_list_on_stack);
  
  	throtl_log(td, "dispatch nr_queued=%lu read=%u write=%u",
  			total_nr_queued(td), td->nr_queued[READ],
  			td->nr_queued[WRITE]);
  
  	nr_disp = throtl_select_dispatch(td, &bio_list_on_stack);
  
  	if (nr_disp)
  		throtl_log(td, "bios disp=%u", nr_disp);
  
  	throtl_schedule_next_dispatch(td);
  out:
  	spin_unlock_irq(q->queue_lock);
  
  	/*
  	 * If we dispatched some requests, unplug the queue to make sure
  	 * immediate dispatch
  	 */
  	if (nr_disp) {

  		blk_start_plug(&plug);

  		while((bio = bio_list_pop(&bio_list_on_stack)))
  			generic_make_request(bio);

  		blk_finish_plug(&plug);

  	}
  	return nr_disp;
  }
  
  void blk_throtl_work(struct work_struct *work)
  {
  	struct throtl_data *td = container_of(work, struct throtl_data,
  					throtl_work.work);
  	struct request_queue *q = td->queue;
  
  	throtl_dispatch(q);
  }
  
  /* Call with queue lock held */

  static void
  throtl_schedule_delayed_work(struct throtl_data *td, unsigned long delay)

  {

  	struct delayed_work *dwork = &td->throtl_work;

  	/* schedule work if limits changed even if no bio is queued */
  	if (total_nr_queued(td) > 0 || td->limits_changed) {

  		/*
  		 * We might have a work scheduled to be executed in future.
  		 * Cancel that and schedule a new one.
  		 */
  		__cancel_delayed_work(dwork);

  		queue_delayed_work(kthrotld_workqueue, dwork, delay);

  		throtl_log(td, "schedule work. delay=%lu jiffies=%lu",
  				delay, jiffies);
  	}
  }

  
  static void
  throtl_destroy_tg(struct throtl_data *td, struct throtl_grp *tg)
  {
  	/* Something wrong if we are trying to remove same group twice */
  	BUG_ON(hlist_unhashed(&tg->tg_node));
  
  	hlist_del_init(&tg->tg_node);
  
  	/*
  	 * Put the reference taken at the time of creation so that when all
  	 * queues are gone, group can be destroyed.
  	 */
  	throtl_put_tg(tg);
  	td->nr_undestroyed_grps--;
  }
  
  static void throtl_release_tgs(struct throtl_data *td)
  {
  	struct hlist_node *pos, *n;
  	struct throtl_grp *tg;
  
  	hlist_for_each_entry_safe(tg, pos, n, &td->tg_list, tg_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 (!blkiocg_del_blkio_group(&tg->blkg))
  			throtl_destroy_tg(td, tg);
  	}
  }
  
  static void throtl_td_free(struct throtl_data *td)
  {
  	kfree(td);
  }
  
  /*
   * 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 throtl_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 queue was going away, cgroup deltion
   * path got to it first.
   */
  void throtl_unlink_blkio_group(void *key, struct blkio_group *blkg)
  {
  	unsigned long flags;
  	struct throtl_data *td = key;
  
  	spin_lock_irqsave(td->queue->queue_lock, flags);
  	throtl_destroy_tg(td, tg_of_blkg(blkg));
  	spin_unlock_irqrestore(td->queue->queue_lock, flags);
  }

  static void throtl_update_blkio_group_common(struct throtl_data *td,
  				struct throtl_grp *tg)
  {
  	xchg(&tg->limits_changed, true);
  	xchg(&td->limits_changed, true);
  	/* Schedule a work now to process the limit change */
  	throtl_schedule_delayed_work(td, 0);
  }

  /*
   * For all update functions, key should be a valid pointer because these
   * update functions are called under blkcg_lock, that means, blkg is

   * valid and in turn key is valid. queue exit path can not race because

   * of blkcg_lock
   *
   * Can not take queue lock in update functions as queue lock under blkcg_lock
   * is not allowed. Under other paths we take blkcg_lock under queue_lock.
   */
  static void throtl_update_blkio_group_read_bps(void *key,
  				struct blkio_group *blkg, u64 read_bps)

  {

  	struct throtl_data *td = key;

  	struct throtl_grp *tg = tg_of_blkg(blkg);

  	tg->bps[READ] = read_bps;
  	throtl_update_blkio_group_common(td, tg);

  }

  static void throtl_update_blkio_group_write_bps(void *key,
  				struct blkio_group *blkg, u64 write_bps)

  {

  	struct throtl_data *td = key;

  	struct throtl_grp *tg = tg_of_blkg(blkg);

  	tg->bps[WRITE] = write_bps;
  	throtl_update_blkio_group_common(td, tg);

  }

  static void throtl_update_blkio_group_read_iops(void *key,
  			struct blkio_group *blkg, unsigned int read_iops)

  {

  	struct throtl_data *td = key;

  	struct throtl_grp *tg = tg_of_blkg(blkg);

  	tg->iops[READ] = read_iops;
  	throtl_update_blkio_group_common(td, tg);

  }

  static void throtl_update_blkio_group_write_iops(void *key,
  			struct blkio_group *blkg, unsigned int write_iops)

  {

  	struct throtl_data *td = key;

  	struct throtl_grp *tg = tg_of_blkg(blkg);

  	tg->iops[WRITE] = write_iops;
  	throtl_update_blkio_group_common(td, tg);

  }

  static void throtl_shutdown_wq(struct request_queue *q)

  {
  	struct throtl_data *td = q->td;
  
  	cancel_delayed_work_sync(&td->throtl_work);
  }
  
  static struct blkio_policy_type blkio_policy_throtl = {
  	.ops = {
  		.blkio_unlink_group_fn = throtl_unlink_blkio_group,
  		.blkio_update_group_read_bps_fn =
  					throtl_update_blkio_group_read_bps,
  		.blkio_update_group_write_bps_fn =
  					throtl_update_blkio_group_write_bps,

  		.blkio_update_group_read_iops_fn =
  					throtl_update_blkio_group_read_iops,
  		.blkio_update_group_write_iops_fn =
  					throtl_update_blkio_group_write_iops,

  	},

  	.plid = BLKIO_POLICY_THROTL,

  };
  
  int blk_throtl_bio(struct request_queue *q, struct bio **biop)
  {
  	struct throtl_data *td = q->td;
  	struct throtl_grp *tg;
  	struct bio *bio = *biop;
  	bool rw = bio_data_dir(bio), update_disptime = true;
  
  	if (bio->bi_rw & REQ_THROTTLED) {
  		bio->bi_rw &= ~REQ_THROTTLED;
  		return 0;
  	}
  
  	spin_lock_irq(q->queue_lock);
  	tg = throtl_get_tg(td);
  
  	if (tg->nr_queued[rw]) {
  		/*
  		 * There is already another bio queued in same dir. No
  		 * need to update dispatch time.
  		 */

  		update_disptime = false;

  		goto queue_bio;

  	}
  
  	/* Bio is with-in rate limit of group */
  	if (tg_may_dispatch(td, tg, bio, NULL)) {
  		throtl_charge_bio(tg, bio);

  
  		/*
  		 * We need to trim slice even when bios are not being queued
  		 * otherwise it might happen that a bio is not queued for
  		 * a long time and slice keeps on extending and trim is not
  		 * called for a long time. Now if limits are reduced suddenly
  		 * we take into account all the IO dispatched so far at new
  		 * low rate and * newly queued IO gets a really long dispatch
  		 * time.
  		 *
  		 * So keep on trimming slice even if bio is not queued.
  		 */
  		throtl_trim_slice(td, tg, rw);

  		goto out;
  	}
  
  queue_bio:

  	throtl_log_tg(td, tg, "[%c] bio. bdisp=%u sz=%u bps=%llu"
  			" iodisp=%u iops=%u queued=%d/%d",
  			rw == READ ? 'R' : 'W',

  			tg->bytes_disp[rw], bio->bi_size, tg->bps[rw],

  			tg->io_disp[rw], tg->iops[rw],

  			tg->nr_queued[READ], tg->nr_queued[WRITE]);
  
  	throtl_add_bio_tg(q->td, tg, bio);
  	*biop = NULL;
  
  	if (update_disptime) {
  		tg_update_disptime(td, tg);
  		throtl_schedule_next_dispatch(td);
  	}
  
  out:
  	spin_unlock_irq(q->queue_lock);
  	return 0;
  }
  
  int blk_throtl_init(struct request_queue *q)
  {
  	struct throtl_data *td;
  	struct throtl_grp *tg;
  
  	td = kzalloc_node(sizeof(*td), GFP_KERNEL, q->node);
  	if (!td)
  		return -ENOMEM;
  
  	INIT_HLIST_HEAD(&td->tg_list);
  	td->tg_service_tree = THROTL_RB_ROOT;

  	td->limits_changed = false;

  
  	/* Init root group */
  	tg = &td->root_tg;
  	INIT_HLIST_NODE(&tg->tg_node);
  	RB_CLEAR_NODE(&tg->rb_node);
  	bio_list_init(&tg->bio_lists[0]);
  	bio_list_init(&tg->bio_lists[1]);
  
  	/* Practically unlimited BW */
  	tg->bps[0] = tg->bps[1] = -1;

  	tg->iops[0] = tg->iops[1] = -1;

  	td->limits_changed = false;

  
  	/*
  	 * Set root group reference to 2. One reference will be dropped when
  	 * all groups on tg_list are being deleted during queue exit. Other
  	 * reference will remain there as we don't want to delete this group
  	 * as it is statically allocated and gets destroyed when throtl_data
  	 * goes away.
  	 */
  	atomic_set(&tg->ref, 2);
  	hlist_add_head(&tg->tg_node, &td->tg_list);
  	td->nr_undestroyed_grps++;

  
  	INIT_DELAYED_WORK(&td->throtl_work, blk_throtl_work);
  
  	rcu_read_lock();
  	blkiocg_add_blkio_group(&blkio_root_cgroup, &tg->blkg, (void *)td,
  					0, BLKIO_POLICY_THROTL);
  	rcu_read_unlock();
  
  	/* Attach throtl data to request queue */
  	td->queue = q;
  	q->td = td;
  	return 0;
  }
  
  void blk_throtl_exit(struct request_queue *q)
  {
  	struct throtl_data *td = q->td;
  	bool wait = false;
  
  	BUG_ON(!td);

  	throtl_shutdown_wq(q);

  
  	spin_lock_irq(q->queue_lock);
  	throtl_release_tgs(td);

  
  	/* If there are other groups */

  	if (td->nr_undestroyed_grps > 0)

  		wait = true;
  
  	spin_unlock_irq(q->queue_lock);
  
  	/*
  	 * Wait for tg->blkg->key accessors to exit their grace periods.
  	 * Do this wait only if there are other undestroyed groups out
  	 * there (other than root group). This can happen if cgroup deletion
  	 * path claimed the responsibility of cleaning up a group before
  	 * queue cleanup code get to the group.
  	 *
  	 * Do not call synchronize_rcu() unconditionally as there are drivers
  	 * which create/delete request queue hundreds of times during scan/boot
  	 * and synchronize_rcu() can take significant time and slow down boot.
  	 */
  	if (wait)
  		synchronize_rcu();

  
  	/*
  	 * Just being safe to make sure after previous flush if some body did
  	 * update limits through cgroup and another work got queued, cancel
  	 * it.
  	 */

  	throtl_shutdown_wq(q);

  	throtl_td_free(td);
  }
  
  static int __init throtl_init(void)
  {

  	kthrotld_workqueue = alloc_workqueue("kthrotld", WQ_MEM_RECLAIM, 0);
  	if (!kthrotld_workqueue)
  		panic("Failed to create kthrotld
  ");

  	blkio_policy_register(&blkio_policy_throtl);
  	return 0;
  }
  
  module_init(throtl_init);