/*
   * 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 <linux/blk-cgroup.h>

  #include "blk.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 */

  static struct blkcg_policy blkcg_policy_throtl;

  /* A workqueue to queue throttle related work */
  static struct workqueue_struct *kthrotld_workqueue;

  /*
   * To implement hierarchical throttling, throtl_grps form a tree and bios
   * are dispatched upwards level by level until they reach the top and get
   * issued.  When dispatching bios from the children and local group at each
   * level, if the bios are dispatched into a single bio_list, there's a risk
   * of a local or child group which can queue many bios at once filling up
   * the list starving others.
   *
   * To avoid such starvation, dispatched bios are queued separately
   * according to where they came from.  When they are again dispatched to
   * the parent, they're popped in round-robin order so that no single source
   * hogs the dispatch window.
   *
   * throtl_qnode is used to keep the queued bios separated by their sources.
   * Bios are queued to throtl_qnode which in turn is queued to
   * throtl_service_queue and then dispatched in round-robin order.
   *
   * It's also used to track the reference counts on blkg's.  A qnode always
   * belongs to a throtl_grp and gets queued on itself or the parent, so
   * incrementing the reference of the associated throtl_grp when a qnode is
   * queued and decrementing when dequeued is enough to keep the whole blkg
   * tree pinned while bios are in flight.
   */
  struct throtl_qnode {
  	struct list_head	node;		/* service_queue->queued[] */
  	struct bio_list		bios;		/* queued bios */
  	struct throtl_grp	*tg;		/* tg this qnode belongs to */
  };

  struct throtl_service_queue {

  	struct throtl_service_queue *parent_sq;	/* the parent service_queue */

  	/*
  	 * Bios queued directly to this service_queue or dispatched from
  	 * children throtl_grp's.
  	 */

  	struct list_head	queued[2];	/* throtl_qnode [READ/WRITE] */

  	unsigned int		nr_queued[2];	/* number of queued bios */
  
  	/*
  	 * RB tree of active children throtl_grp's, which are sorted by
  	 * their ->disptime.
  	 */

  	struct rb_root		pending_tree;	/* RB tree of active tgs */
  	struct rb_node		*first_pending;	/* first node in the tree */
  	unsigned int		nr_pending;	/* # queued in the tree */
  	unsigned long		first_pending_disptime;	/* disptime of the first tg */

  	struct timer_list	pending_timer;	/* fires on first_pending_disptime */

  };

  enum tg_state_flags {
  	THROTL_TG_PENDING	= 1 << 0,	/* on parent's pending tree */

  	THROTL_TG_WAS_EMPTY	= 1 << 1,	/* bio_lists[] became non-empty */

  };

  #define rb_entry_tg(node)	rb_entry((node), struct throtl_grp, rb_node)
  
  struct throtl_grp {

  	/* must be the first member */
  	struct blkg_policy_data pd;

  	/* active throtl group service_queue member */

  	struct rb_node rb_node;

  	/* throtl_data this group belongs to */
  	struct throtl_data *td;

  	/* this group's service queue */
  	struct throtl_service_queue service_queue;

  	/*

  	 * qnode_on_self is used when bios are directly queued to this
  	 * throtl_grp so that local bios compete fairly with bios
  	 * dispatched from children.  qnode_on_parent is used when bios are
  	 * dispatched from this throtl_grp into its parent and will compete
  	 * with the sibling qnode_on_parents and the parent's
  	 * qnode_on_self.
  	 */
  	struct throtl_qnode qnode_on_self[2];
  	struct throtl_qnode qnode_on_parent[2];
  
  	/*

  	 * 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;

  	unsigned int flags;

  	/* are there any throtl rules between this group and td? */
  	bool has_rules[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];
  };
  
  struct throtl_data
  {

  	/* service tree for active throtl groups */

  	struct throtl_service_queue service_queue;

  	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 work_struct dispatch_work;

  };

  static void throtl_pending_timer_fn(unsigned long arg);

  static inline struct throtl_grp *pd_to_tg(struct blkg_policy_data *pd)
  {
  	return pd ? container_of(pd, struct throtl_grp, pd) : NULL;
  }

  static inline struct throtl_grp *blkg_to_tg(struct blkcg_gq *blkg)

  {

  	return pd_to_tg(blkg_to_pd(blkg, &blkcg_policy_throtl));

  }

  static inline struct blkcg_gq *tg_to_blkg(struct throtl_grp *tg)

  {

  	return pd_to_blkg(&tg->pd);

  }

  /**
   * sq_to_tg - return the throl_grp the specified service queue belongs to
   * @sq: the throtl_service_queue of interest
   *
   * Return the throtl_grp @sq belongs to.  If @sq is the top-level one
   * embedded in throtl_data, %NULL is returned.
   */
  static struct throtl_grp *sq_to_tg(struct throtl_service_queue *sq)
  {
  	if (sq && sq->parent_sq)
  		return container_of(sq, struct throtl_grp, service_queue);
  	else
  		return NULL;
  }
  
  /**
   * sq_to_td - return throtl_data the specified service queue belongs to
   * @sq: the throtl_service_queue of interest
   *
   * A service_queue can be embeded in either a throtl_grp or throtl_data.
   * Determine the associated throtl_data accordingly and return it.
   */
  static struct throtl_data *sq_to_td(struct throtl_service_queue *sq)
  {
  	struct throtl_grp *tg = sq_to_tg(sq);
  
  	if (tg)
  		return tg->td;
  	else
  		return container_of(sq, struct throtl_data, service_queue);
  }
  
  /**
   * throtl_log - log debug message via blktrace
   * @sq: the service_queue being reported
   * @fmt: printf format string
   * @args: printf args
   *
   * The messages are prefixed with "throtl BLKG_NAME" if @sq belongs to a
   * throtl_grp; otherwise, just "throtl".

   */
  #define throtl_log(sq, fmt, args...)	do {				\
  	struct throtl_grp *__tg = sq_to_tg((sq));			\
  	struct throtl_data *__td = sq_to_td((sq));			\
  									\
  	(void)__td;							\

  	if (likely(!blk_trace_note_message_enabled(__td->queue)))	\
  		break;							\

  	if ((__tg)) {							\
  		char __pbuf[128];					\

  									\

  		blkg_path(tg_to_blkg(__tg), __pbuf, sizeof(__pbuf));	\
  		blk_add_trace_msg(__td->queue, "throtl %s " fmt, __pbuf, ##args); \
  	} else {							\
  		blk_add_trace_msg(__td->queue, "throtl " fmt, ##args);	\
  	}								\

  } while (0)

  static void throtl_qnode_init(struct throtl_qnode *qn, struct throtl_grp *tg)
  {
  	INIT_LIST_HEAD(&qn->node);
  	bio_list_init(&qn->bios);
  	qn->tg = tg;
  }
  
  /**
   * throtl_qnode_add_bio - add a bio to a throtl_qnode and activate it
   * @bio: bio being added
   * @qn: qnode to add bio to
   * @queued: the service_queue->queued[] list @qn belongs to
   *
   * Add @bio to @qn and put @qn on @queued if it's not already on.
   * @qn->tg's reference count is bumped when @qn is activated.  See the
   * comment on top of throtl_qnode definition for details.
   */
  static void throtl_qnode_add_bio(struct bio *bio, struct throtl_qnode *qn,
  				 struct list_head *queued)
  {
  	bio_list_add(&qn->bios, bio);
  	if (list_empty(&qn->node)) {
  		list_add_tail(&qn->node, queued);
  		blkg_get(tg_to_blkg(qn->tg));
  	}
  }
  
  /**
   * throtl_peek_queued - peek the first bio on a qnode list
   * @queued: the qnode list to peek
   */
  static struct bio *throtl_peek_queued(struct list_head *queued)
  {
  	struct throtl_qnode *qn = list_first_entry(queued, struct throtl_qnode, node);
  	struct bio *bio;
  
  	if (list_empty(queued))
  		return NULL;
  
  	bio = bio_list_peek(&qn->bios);
  	WARN_ON_ONCE(!bio);
  	return bio;
  }
  
  /**
   * throtl_pop_queued - pop the first bio form a qnode list
   * @queued: the qnode list to pop a bio from
   * @tg_to_put: optional out argument for throtl_grp to put
   *
   * Pop the first bio from the qnode list @queued.  After popping, the first
   * qnode is removed from @queued if empty or moved to the end of @queued so
   * that the popping order is round-robin.
   *
   * When the first qnode is removed, its associated throtl_grp should be put
   * too.  If @tg_to_put is NULL, this function automatically puts it;
   * otherwise, *@tg_to_put is set to the throtl_grp to put and the caller is
   * responsible for putting it.
   */
  static struct bio *throtl_pop_queued(struct list_head *queued,
  				     struct throtl_grp **tg_to_put)
  {
  	struct throtl_qnode *qn = list_first_entry(queued, struct throtl_qnode, node);
  	struct bio *bio;
  
  	if (list_empty(queued))
  		return NULL;
  
  	bio = bio_list_pop(&qn->bios);
  	WARN_ON_ONCE(!bio);
  
  	if (bio_list_empty(&qn->bios)) {
  		list_del_init(&qn->node);
  		if (tg_to_put)
  			*tg_to_put = qn->tg;
  		else
  			blkg_put(tg_to_blkg(qn->tg));
  	} else {
  		list_move_tail(&qn->node, queued);
  	}
  
  	return bio;
  }

  /* init a service_queue, assumes the caller zeroed it */

  static void throtl_service_queue_init(struct throtl_service_queue *sq)

  {

  	INIT_LIST_HEAD(&sq->queued[0]);
  	INIT_LIST_HEAD(&sq->queued[1]);

  	sq->pending_tree = RB_ROOT;

  	setup_timer(&sq->pending_timer, throtl_pending_timer_fn,
  		    (unsigned long)sq);
  }

  static struct blkg_policy_data *throtl_pd_alloc(gfp_t gfp, int node)
  {

  	struct throtl_grp *tg;

  	int rw;

  
  	tg = kzalloc_node(sizeof(*tg), gfp, node);
  	if (!tg)

  		return NULL;

  	throtl_service_queue_init(&tg->service_queue);
  
  	for (rw = READ; rw <= WRITE; rw++) {
  		throtl_qnode_init(&tg->qnode_on_self[rw], tg);
  		throtl_qnode_init(&tg->qnode_on_parent[rw], tg);
  	}
  
  	RB_CLEAR_NODE(&tg->rb_node);
  	tg->bps[READ] = -1;
  	tg->bps[WRITE] = -1;
  	tg->iops[READ] = -1;
  	tg->iops[WRITE] = -1;

  	return &tg->pd;

  }

  static void throtl_pd_init(struct blkg_policy_data *pd)

  {

  	struct throtl_grp *tg = pd_to_tg(pd);
  	struct blkcg_gq *blkg = tg_to_blkg(tg);

  	struct throtl_data *td = blkg->q->td;

  	struct throtl_service_queue *sq = &tg->service_queue;

  	/*

  	 * If on the default hierarchy, we switch to properly hierarchical

  	 * behavior where limits on a given throtl_grp are applied to the
  	 * whole subtree rather than just the group itself.  e.g. If 16M
  	 * read_bps limit is set on the root group, the whole system can't
  	 * exceed 16M for the device.
  	 *

  	 * If not on the default hierarchy, the broken flat hierarchy

  	 * behavior is retained where all throtl_grps are treated as if
  	 * they're all separate root groups right below throtl_data.
  	 * Limits of a group don't interact with limits of other groups
  	 * regardless of the position of the group in the hierarchy.
  	 */

  	sq->parent_sq = &td->service_queue;

  	if (cgroup_subsys_on_dfl(io_cgrp_subsys) && blkg->parent)

  		sq->parent_sq = &blkg_to_tg(blkg->parent)->service_queue;

  	tg->td = td;

  }

  /*
   * Set has_rules[] if @tg or any of its parents have limits configured.
   * This doesn't require walking up to the top of the hierarchy as the
   * parent's has_rules[] is guaranteed to be correct.
   */
  static void tg_update_has_rules(struct throtl_grp *tg)
  {
  	struct throtl_grp *parent_tg = sq_to_tg(tg->service_queue.parent_sq);
  	int rw;
  
  	for (rw = READ; rw <= WRITE; rw++)
  		tg->has_rules[rw] = (parent_tg && parent_tg->has_rules[rw]) ||
  				    (tg->bps[rw] != -1 || tg->iops[rw] != -1);
  }

  static void throtl_pd_online(struct blkg_policy_data *pd)

  {
  	/*
  	 * We don't want new groups to escape the limits of its ancestors.
  	 * Update has_rules[] after a new group is brought online.
  	 */

  	tg_update_has_rules(pd_to_tg(pd));

  }

  static void throtl_pd_free(struct blkg_policy_data *pd)
  {

  	struct throtl_grp *tg = pd_to_tg(pd);

  	del_timer_sync(&tg->service_queue.pending_timer);

  	kfree(tg);

  }

  static struct throtl_grp *
  throtl_rb_first(struct throtl_service_queue *parent_sq)

  {
  	/* Service tree is empty */

  	if (!parent_sq->nr_pending)

  		return NULL;

  	if (!parent_sq->first_pending)
  		parent_sq->first_pending = rb_first(&parent_sq->pending_tree);

  	if (parent_sq->first_pending)
  		return rb_entry_tg(parent_sq->first_pending);

  
  	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_service_queue *parent_sq)

  {

  	if (parent_sq->first_pending == n)
  		parent_sq->first_pending = NULL;
  	rb_erase_init(n, &parent_sq->pending_tree);
  	--parent_sq->nr_pending;

  }

  static void update_min_dispatch_time(struct throtl_service_queue *parent_sq)

  {
  	struct throtl_grp *tg;

  	tg = throtl_rb_first(parent_sq);

  	if (!tg)
  		return;

  	parent_sq->first_pending_disptime = tg->disptime;

  }

  static void tg_service_queue_add(struct throtl_grp *tg)

  {

  	struct throtl_service_queue *parent_sq = tg->service_queue.parent_sq;

  	struct rb_node **node = &parent_sq->pending_tree.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)

  		parent_sq->first_pending = &tg->rb_node;

  
  	rb_link_node(&tg->rb_node, parent, node);

  	rb_insert_color(&tg->rb_node, &parent_sq->pending_tree);

  }

  static void __throtl_enqueue_tg(struct throtl_grp *tg)

  {

  	tg_service_queue_add(tg);

  	tg->flags |= THROTL_TG_PENDING;

  	tg->service_queue.parent_sq->nr_pending++;

  }

  static void throtl_enqueue_tg(struct throtl_grp *tg)

  {

  	if (!(tg->flags & THROTL_TG_PENDING))

  		__throtl_enqueue_tg(tg);

  }

  static void __throtl_dequeue_tg(struct throtl_grp *tg)

  {

  	throtl_rb_erase(&tg->rb_node, tg->service_queue.parent_sq);

  	tg->flags &= ~THROTL_TG_PENDING;

  }

  static void throtl_dequeue_tg(struct throtl_grp *tg)

  {

  	if (tg->flags & THROTL_TG_PENDING)

  		__throtl_dequeue_tg(tg);

  }

  /* Call with queue lock held */

  static void throtl_schedule_pending_timer(struct throtl_service_queue *sq,
  					  unsigned long expires)

  {

  	mod_timer(&sq->pending_timer, expires);
  	throtl_log(sq, "schedule timer. delay=%lu jiffies=%lu",
  		   expires - jiffies, jiffies);

  }

  /**
   * throtl_schedule_next_dispatch - schedule the next dispatch cycle
   * @sq: the service_queue to schedule dispatch for
   * @force: force scheduling
   *
   * Arm @sq->pending_timer so that the next dispatch cycle starts on the
   * dispatch time of the first pending child.  Returns %true if either timer
   * is armed or there's no pending child left.  %false if the current
   * dispatch window is still open and the caller should continue
   * dispatching.
   *
   * If @force is %true, the dispatch timer is always scheduled and this
   * function is guaranteed to return %true.  This is to be used when the
   * caller can't dispatch itself and needs to invoke pending_timer
   * unconditionally.  Note that forced scheduling is likely to induce short
   * delay before dispatch starts even if @sq->first_pending_disptime is not
   * in the future and thus shouldn't be used in hot paths.
   */
  static bool throtl_schedule_next_dispatch(struct throtl_service_queue *sq,
  					  bool force)

  {

  	/* any pending children left? */

  	if (!sq->nr_pending)

  		return true;

  	update_min_dispatch_time(sq);

  	/* is the next dispatch time in the future? */

  	if (force || time_after(sq->first_pending_disptime, jiffies)) {

  		throtl_schedule_pending_timer(sq, sq->first_pending_disptime);

  		return true;

  	}

  	/* tell the caller to continue dispatching */
  	return false;

  }

  static inline void throtl_start_new_slice_with_credit(struct throtl_grp *tg,
  		bool rw, unsigned long start)
  {
  	tg->bytes_disp[rw] = 0;
  	tg->io_disp[rw] = 0;
  
  	/*
  	 * Previous slice has expired. We must have trimmed it after last
  	 * bio dispatch. That means since start of last slice, we never used
  	 * that bandwidth. Do try to make use of that bandwidth while giving
  	 * credit.
  	 */
  	if (time_after_eq(start, tg->slice_start[rw]))
  		tg->slice_start[rw] = start;
  
  	tg->slice_end[rw] = jiffies + throtl_slice;
  	throtl_log(&tg->service_queue,
  		   "[%c] new slice with credit start=%lu end=%lu jiffies=%lu",
  		   rw == READ ? 'R' : 'W', tg->slice_start[rw],
  		   tg->slice_end[rw], jiffies);
  }

  static inline void throtl_start_new_slice(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->service_queue,
  		   "[%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_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_grp *tg, bool rw,
  				       unsigned long jiffy_end)

  {
  	tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);

  	throtl_log(&tg->service_queue,
  		   "[%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_grp *tg, bool rw)

  {
  	if (time_in_range(jiffies, tg->slice_start[rw], tg->slice_end[rw]))

  		return false;

  
  	return 1;
  }
  
  /* Trim the used slices and adjust slice start accordingly */

  static inline void throtl_trim_slice(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(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(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->service_queue,
  		   "[%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_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 true;

  	}

  	/* 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_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_iter.bi_size <= bytes_allowed) {

  		if (wait)
  			*wait = 0;

  		return true;

  	}
  
  	/* Calc approx time to dispatch */

  	extra_bytes = tg->bytes_disp[rw] + bio->bi_iter.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_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->service_queue.nr_queued[rw] &&

  	       bio != throtl_peek_queued(&tg->service_queue.queued[rw]));

  	/* If tg->bps = -1, then BW is unlimited */
  	if (tg->bps[rw] == -1 && tg->iops[rw] == -1) {
  		if (wait)
  			*wait = 0;

  		return true;

  	}
  
  	/*
  	 * 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(tg, rw))
  		throtl_start_new_slice(tg, rw);

  	else {
  		if (time_before(tg->slice_end[rw], jiffies + throtl_slice))

  			throtl_extend_slice(tg, rw, jiffies + throtl_slice);

  	}

  	if (tg_with_in_bps_limit(tg, bio, &bps_wait) &&
  	    tg_with_in_iops_limit(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(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);

  
  	/* Charge the bio to the group */

  	tg->bytes_disp[rw] += bio->bi_iter.bi_size;

  	tg->io_disp[rw]++;

  	/*
  	 * REQ_THROTTLED is used to prevent the same bio to be throttled
  	 * more than once as a throttled bio will go through blk-throtl the
  	 * second time when it eventually gets issued.  Set it when a bio
  	 * is being charged to a tg.

  	 */

  	if (!(bio->bi_rw & REQ_THROTTLED))

  		bio->bi_rw |= REQ_THROTTLED;

  }

  /**
   * throtl_add_bio_tg - add a bio to the specified throtl_grp
   * @bio: bio to add
   * @qn: qnode to use
   * @tg: the target throtl_grp
   *
   * Add @bio to @tg's service_queue using @qn.  If @qn is not specified,
   * tg->qnode_on_self[] is used.
   */
  static void throtl_add_bio_tg(struct bio *bio, struct throtl_qnode *qn,
  			      struct throtl_grp *tg)

  {

  	struct throtl_service_queue *sq = &tg->service_queue;

  	bool rw = bio_data_dir(bio);

  	if (!qn)
  		qn = &tg->qnode_on_self[rw];

  	/*
  	 * If @tg doesn't currently have any bios queued in the same
  	 * direction, queueing @bio can change when @tg should be
  	 * dispatched.  Mark that @tg was empty.  This is automatically
  	 * cleaered on the next tg_update_disptime().
  	 */
  	if (!sq->nr_queued[rw])
  		tg->flags |= THROTL_TG_WAS_EMPTY;

  	throtl_qnode_add_bio(bio, qn, &sq->queued[rw]);

  	sq->nr_queued[rw]++;

  	throtl_enqueue_tg(tg);

  }

  static void tg_update_disptime(struct throtl_grp *tg)

  {

  	struct throtl_service_queue *sq = &tg->service_queue;

  	unsigned long read_wait = -1, write_wait = -1, min_wait = -1, disptime;
  	struct bio *bio;

  	if ((bio = throtl_peek_queued(&sq->queued[READ])))

  		tg_may_dispatch(tg, bio, &read_wait);

  	if ((bio = throtl_peek_queued(&sq->queued[WRITE])))

  		tg_may_dispatch(tg, bio, &write_wait);

  
  	min_wait = min(read_wait, write_wait);
  	disptime = jiffies + min_wait;

  	/* Update dispatch time */

  	throtl_dequeue_tg(tg);

  	tg->disptime = disptime;

  	throtl_enqueue_tg(tg);

  
  	/* see throtl_add_bio_tg() */
  	tg->flags &= ~THROTL_TG_WAS_EMPTY;

  }

  static void start_parent_slice_with_credit(struct throtl_grp *child_tg,
  					struct throtl_grp *parent_tg, bool rw)
  {
  	if (throtl_slice_used(parent_tg, rw)) {
  		throtl_start_new_slice_with_credit(parent_tg, rw,
  				child_tg->slice_start[rw]);
  	}
  
  }

  static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)

  {

  	struct throtl_service_queue *sq = &tg->service_queue;

  	struct throtl_service_queue *parent_sq = sq->parent_sq;
  	struct throtl_grp *parent_tg = sq_to_tg(parent_sq);

  	struct throtl_grp *tg_to_put = NULL;

  	struct bio *bio;

  	/*
  	 * @bio is being transferred from @tg to @parent_sq.  Popping a bio
  	 * from @tg may put its reference and @parent_sq might end up
  	 * getting released prematurely.  Remember the tg to put and put it
  	 * after @bio is transferred to @parent_sq.
  	 */
  	bio = throtl_pop_queued(&sq->queued[rw], &tg_to_put);

  	sq->nr_queued[rw]--;

  
  	throtl_charge_bio(tg, bio);

  
  	/*
  	 * If our parent is another tg, we just need to transfer @bio to
  	 * the parent using throtl_add_bio_tg().  If our parent is
  	 * @td->service_queue, @bio is ready to be issued.  Put it on its
  	 * bio_lists[] and decrease total number queued.  The caller is
  	 * responsible for issuing these bios.
  	 */
  	if (parent_tg) {

  		throtl_add_bio_tg(bio, &tg->qnode_on_parent[rw], parent_tg);

  		start_parent_slice_with_credit(tg, parent_tg, rw);

  	} else {

  		throtl_qnode_add_bio(bio, &tg->qnode_on_parent[rw],
  				     &parent_sq->queued[rw]);

  		BUG_ON(tg->td->nr_queued[rw] <= 0);
  		tg->td->nr_queued[rw]--;
  	}

  	throtl_trim_slice(tg, rw);

  	if (tg_to_put)
  		blkg_put(tg_to_blkg(tg_to_put));

  }

  static int throtl_dispatch_tg(struct throtl_grp *tg)

  {

  	struct throtl_service_queue *sq = &tg->service_queue;

  	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 = throtl_peek_queued(&sq->queued[READ])) &&

  	       tg_may_dispatch(tg, bio, NULL)) {

  		tg_dispatch_one_bio(tg, bio_data_dir(bio));

  		nr_reads++;
  
  		if (nr_reads >= max_nr_reads)
  			break;
  	}

  	while ((bio = throtl_peek_queued(&sq->queued[WRITE])) &&

  	       tg_may_dispatch(tg, bio, NULL)) {

  		tg_dispatch_one_bio(tg, bio_data_dir(bio));

  		nr_writes++;
  
  		if (nr_writes >= max_nr_writes)
  			break;
  	}
  
  	return nr_reads + nr_writes;
  }

  static int throtl_select_dispatch(struct throtl_service_queue *parent_sq)

  {
  	unsigned int nr_disp = 0;

  
  	while (1) {

  		struct throtl_grp *tg = throtl_rb_first(parent_sq);
  		struct throtl_service_queue *sq = &tg->service_queue;

  
  		if (!tg)
  			break;
  
  		if (time_before(jiffies, tg->disptime))
  			break;

  		throtl_dequeue_tg(tg);

  		nr_disp += throtl_dispatch_tg(tg);

  		if (sq->nr_queued[0] || sq->nr_queued[1])

  			tg_update_disptime(tg);

  
  		if (nr_disp >= throtl_quantum)
  			break;
  	}
  
  	return nr_disp;
  }

  /**
   * throtl_pending_timer_fn - timer function for service_queue->pending_timer
   * @arg: the throtl_service_queue being serviced
   *
   * This timer is armed when a child throtl_grp with active bio's become
   * pending and queued on the service_queue's pending_tree and expires when
   * the first child throtl_grp should be dispatched.  This function

   * dispatches bio's from the children throtl_grps to the parent
   * service_queue.
   *
   * If the parent's parent is another throtl_grp, dispatching is propagated
   * by either arming its pending_timer or repeating dispatch directly.  If
   * the top-level service_tree is reached, throtl_data->dispatch_work is
   * kicked so that the ready bio's are issued.

   */

  static void throtl_pending_timer_fn(unsigned long arg)
  {
  	struct throtl_service_queue *sq = (void *)arg;

  	struct throtl_grp *tg = sq_to_tg(sq);

  	struct throtl_data *td = sq_to_td(sq);

  	struct request_queue *q = td->queue;

  	struct throtl_service_queue *parent_sq;
  	bool dispatched;

  	int ret;

  
  	spin_lock_irq(q->queue_lock);

  again:
  	parent_sq = sq->parent_sq;
  	dispatched = false;

  	while (true) {
  		throtl_log(sq, "dispatch nr_queued=%u read=%u write=%u",

  			   sq->nr_queued[READ] + sq->nr_queued[WRITE],
  			   sq->nr_queued[READ], sq->nr_queued[WRITE]);

  
  		ret = throtl_select_dispatch(sq);
  		if (ret) {

  			throtl_log(sq, "bios disp=%u", ret);
  			dispatched = true;
  		}

  		if (throtl_schedule_next_dispatch(sq, false))
  			break;

  		/* this dispatch windows is still open, relax and repeat */
  		spin_unlock_irq(q->queue_lock);
  		cpu_relax();
  		spin_lock_irq(q->queue_lock);

  	}

  	if (!dispatched)
  		goto out_unlock;

  	if (parent_sq) {
  		/* @parent_sq is another throl_grp, propagate dispatch */
  		if (tg->flags & THROTL_TG_WAS_EMPTY) {
  			tg_update_disptime(tg);
  			if (!throtl_schedule_next_dispatch(parent_sq, false)) {
  				/* window is already open, repeat dispatching */
  				sq = parent_sq;
  				tg = sq_to_tg(sq);
  				goto again;
  			}
  		}
  	} else {
  		/* reached the top-level, queue issueing */
  		queue_work(kthrotld_workqueue, &td->dispatch_work);
  	}
  out_unlock:

  	spin_unlock_irq(q->queue_lock);

  }

  /**
   * blk_throtl_dispatch_work_fn - work function for throtl_data->dispatch_work
   * @work: work item being executed
   *
   * This function is queued for execution when bio's reach the bio_lists[]
   * of throtl_data->service_queue.  Those bio's are ready and issued by this
   * function.
   */

  static void blk_throtl_dispatch_work_fn(struct work_struct *work)

  {
  	struct throtl_data *td = container_of(work, struct throtl_data,
  					      dispatch_work);
  	struct throtl_service_queue *td_sq = &td->service_queue;
  	struct request_queue *q = td->queue;
  	struct bio_list bio_list_on_stack;
  	struct bio *bio;
  	struct blk_plug plug;
  	int rw;
  
  	bio_list_init(&bio_list_on_stack);
  
  	spin_lock_irq(q->queue_lock);

  	for (rw = READ; rw <= WRITE; rw++)
  		while ((bio = throtl_pop_queued(&td_sq->queued[rw], NULL)))
  			bio_list_add(&bio_list_on_stack, bio);

  	spin_unlock_irq(q->queue_lock);
  
  	if (!bio_list_empty(&bio_list_on_stack)) {

  		blk_start_plug(&plug);

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

  		blk_finish_plug(&plug);

  	}

  }

  static u64 tg_prfill_conf_u64(struct seq_file *sf, struct blkg_policy_data *pd,
  			      int off)

  {

  	struct throtl_grp *tg = pd_to_tg(pd);
  	u64 v = *(u64 *)((void *)tg + off);

  	if (v == -1)

  		return 0;

  	return __blkg_prfill_u64(sf, pd, v);

  }

  static u64 tg_prfill_conf_uint(struct seq_file *sf, struct blkg_policy_data *pd,
  			       int off)

  {

  	struct throtl_grp *tg = pd_to_tg(pd);
  	unsigned int v = *(unsigned int *)((void *)tg + off);

  	if (v == -1)
  		return 0;

  	return __blkg_prfill_u64(sf, pd, v);

  }

  static int tg_print_conf_u64(struct seq_file *sf, void *v)

  {

  	blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_conf_u64,
  			  &blkcg_policy_throtl, seq_cft(sf)->private, false);

  	return 0;

  }

  static int tg_print_conf_uint(struct seq_file *sf, void *v)

  {

  	blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_conf_uint,
  			  &blkcg_policy_throtl, seq_cft(sf)->private, false);

  	return 0;

  }

  static void tg_conf_updated(struct throtl_grp *tg)

  {

  	struct throtl_service_queue *sq = &tg->service_queue;

  	struct cgroup_subsys_state *pos_css;

  	struct blkcg_gq *blkg;

  	throtl_log(&tg->service_queue,
  		   "limit change rbps=%llu wbps=%llu riops=%u wiops=%u",
  		   tg->bps[READ], tg->bps[WRITE],
  		   tg->iops[READ], tg->iops[WRITE]);

  
  	/*

  	 * Update has_rules[] flags for the updated tg's subtree.  A tg is
  	 * considered to have rules if either the tg itself or any of its
  	 * ancestors has rules.  This identifies groups without any
  	 * restrictions in the whole hierarchy and allows them to bypass
  	 * blk-throttle.
  	 */

  	blkg_for_each_descendant_pre(blkg, pos_css, tg_to_blkg(tg))

  		tg_update_has_rules(blkg_to_tg(blkg));
  
  	/*

  	 * We're already holding queue_lock and know @tg is valid.  Let's
  	 * apply the new config directly.
  	 *
  	 * 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(tg, 0);
  	throtl_start_new_slice(tg, 1);

  	if (tg->flags & THROTL_TG_PENDING) {

  		tg_update_disptime(tg);

  		throtl_schedule_next_dispatch(sq->parent_sq, true);

  	}

  }
  
  static ssize_t tg_set_conf(struct kernfs_open_file *of,
  			   char *buf, size_t nbytes, loff_t off, bool is_u64)
  {
  	struct blkcg *blkcg = css_to_blkcg(of_css(of));
  	struct blkg_conf_ctx ctx;
  	struct throtl_grp *tg;
  	int ret;
  	u64 v;
  
  	ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, buf, &ctx);
  	if (ret)
  		return ret;
  
  	ret = -EINVAL;
  	if (sscanf(ctx.body, "%llu", &v) != 1)
  		goto out_finish;
  	if (!v)
  		v = -1;
  
  	tg = blkg_to_tg(ctx.blkg);
  
  	if (is_u64)
  		*(u64 *)((void *)tg + of_cft(of)->private) = v;
  	else
  		*(unsigned int *)((void *)tg + of_cft(of)->private) = v;

  	tg_conf_updated(tg);

  	ret = 0;
  out_finish:

  	blkg_conf_finish(&ctx);

  	return ret ?: nbytes;

  }

  static ssize_t tg_set_conf_u64(struct kernfs_open_file *of,
  			       char *buf, size_t nbytes, loff_t off)

  {

  	return tg_set_conf(of, buf, nbytes, off, true);

  }

  static ssize_t tg_set_conf_uint(struct kernfs_open_file *of,
  				char *buf, size_t nbytes, loff_t off)

  {

  	return tg_set_conf(of, buf, nbytes, off, false);

  }

  static struct cftype throtl_legacy_files[] = {

  	{
  		.name = "throttle.read_bps_device",

  		.private = offsetof(struct throtl_grp, bps[READ]),

  		.seq_show = tg_print_conf_u64,

  		.write = tg_set_conf_u64,

  	},
  	{
  		.name = "throttle.write_bps_device",

  		.private = offsetof(struct throtl_grp, bps[WRITE]),

  		.seq_show = tg_print_conf_u64,

  		.write = tg_set_conf_u64,

  	},
  	{
  		.name = "throttle.read_iops_device",

  		.private = offsetof(struct throtl_grp, iops[READ]),

  		.seq_show = tg_print_conf_uint,

  		.write = tg_set_conf_uint,

  	},
  	{
  		.name = "throttle.write_iops_device",

  		.private = offsetof(struct throtl_grp, iops[WRITE]),

  		.seq_show = tg_print_conf_uint,

  		.write = tg_set_conf_uint,

  	},
  	{
  		.name = "throttle.io_service_bytes",

  		.private = (unsigned long)&blkcg_policy_throtl,
  		.seq_show = blkg_print_stat_bytes,

  	},
  	{
  		.name = "throttle.io_serviced",

  		.private = (unsigned long)&blkcg_policy_throtl,
  		.seq_show = blkg_print_stat_ios,

  	},
  	{ }	/* terminate */
  };

  static u64 tg_prfill_max(struct seq_file *sf, struct blkg_policy_data *pd,
  			 int off)
  {
  	struct throtl_grp *tg = pd_to_tg(pd);
  	const char *dname = blkg_dev_name(pd->blkg);
  	char bufs[4][21] = { "max", "max", "max", "max" };
  
  	if (!dname)
  		return 0;
  	if (tg->bps[READ] == -1 && tg->bps[WRITE] == -1 &&
  	    tg->iops[READ] == -1 && tg->iops[WRITE] == -1)
  		return 0;
  
  	if (tg->bps[READ] != -1)
  		snprintf(bufs[0], sizeof(bufs[0]), "%llu", tg->bps[READ]);
  	if (tg->bps[WRITE] != -1)
  		snprintf(bufs[1], sizeof(bufs[1]), "%llu", tg->bps[WRITE]);
  	if (tg->iops[READ] != -1)
  		snprintf(bufs[2], sizeof(bufs[2]), "%u", tg->iops[READ]);
  	if (tg->iops[WRITE] != -1)
  		snprintf(bufs[3], sizeof(bufs[3]), "%u", tg->iops[WRITE]);
  
  	seq_printf(sf, "%s rbps=%s wbps=%s riops=%s wiops=%s
  ",
  		   dname, bufs[0], bufs[1], bufs[2], bufs[3]);
  	return 0;
  }
  
  static int tg_print_max(struct seq_file *sf, void *v)
  {
  	blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_max,
  			  &blkcg_policy_throtl, seq_cft(sf)->private, false);
  	return 0;
  }
  
  static ssize_t tg_set_max(struct kernfs_open_file *of,
  			  char *buf, size_t nbytes, loff_t off)
  {
  	struct blkcg *blkcg = css_to_blkcg(of_css(of));
  	struct blkg_conf_ctx ctx;
  	struct throtl_grp *tg;
  	u64 v[4];
  	int ret;
  
  	ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, buf, &ctx);
  	if (ret)
  		return ret;
  
  	tg = blkg_to_tg(ctx.blkg);
  
  	v[0] = tg->bps[READ];
  	v[1] = tg->bps[WRITE];
  	v[2] = tg->iops[READ];
  	v[3] = tg->iops[WRITE];
  
  	while (true) {
  		char tok[27];	/* wiops=18446744073709551616 */
  		char *p;
  		u64 val = -1;
  		int len;
  
  		if (sscanf(ctx.body, "%26s%n", tok, &len) != 1)
  			break;
  		if (tok[0] == '\0')
  			break;
  		ctx.body += len;
  
  		ret = -EINVAL;
  		p = tok;
  		strsep(&p, "=");
  		if (!p || (sscanf(p, "%llu", &val) != 1 && strcmp(p, "max")))
  			goto out_finish;
  
  		ret = -ERANGE;
  		if (!val)
  			goto out_finish;
  
  		ret = -EINVAL;
  		if (!strcmp(tok, "rbps"))
  			v[0] = val;
  		else if (!strcmp(tok, "wbps"))
  			v[1] = val;
  		else if (!strcmp(tok, "riops"))
  			v[2] = min_t(u64, val, UINT_MAX);
  		else if (!strcmp(tok, "wiops"))
  			v[3] = min_t(u64, val, UINT_MAX);
  		else
  			goto out_finish;
  	}
  
  	tg->bps[READ] = v[0];
  	tg->bps[WRITE] = v[1];
  	tg->iops[READ] = v[2];
  	tg->iops[WRITE] = v[3];
  
  	tg_conf_updated(tg);
  	ret = 0;
  out_finish:
  	blkg_conf_finish(&ctx);
  	return ret ?: nbytes;
  }
  
  static struct cftype throtl_files[] = {
  	{
  		.name = "max",
  		.flags = CFTYPE_NOT_ON_ROOT,
  		.seq_show = tg_print_max,
  		.write = tg_set_max,
  	},
  	{ }	/* terminate */
  };

  static void throtl_shutdown_wq(struct request_queue *q)

  {
  	struct throtl_data *td = q->td;

  	cancel_work_sync(&td->dispatch_work);

  }

  static struct blkcg_policy blkcg_policy_throtl = {

  	.dfl_cftypes		= throtl_files,

  	.legacy_cftypes		= throtl_legacy_files,

  	.pd_alloc_fn		= throtl_pd_alloc,

  	.pd_init_fn		= throtl_pd_init,

  	.pd_online_fn		= throtl_pd_online,

  	.pd_free_fn		= throtl_pd_free,

  };

  bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
  		    struct bio *bio)

  {

  	struct throtl_qnode *qn = NULL;

  	struct throtl_grp *tg = blkg_to_tg(blkg ?: q->root_blkg);

  	struct throtl_service_queue *sq;

  	bool rw = bio_data_dir(bio);

  	bool throttled = false;

  	WARN_ON_ONCE(!rcu_read_lock_held());

  	/* see throtl_charge_bio() */

  	if ((bio->bi_rw & REQ_THROTTLED) || !tg->has_rules[rw])

  		goto out;

  
  	spin_lock_irq(q->queue_lock);

  
  	if (unlikely(blk_queue_bypass(q)))

  		goto out_unlock;

  	sq = &tg->service_queue;

  	while (true) {
  		/* throtl is FIFO - if bios are already queued, should queue */
  		if (sq->nr_queued[rw])
  			break;

  		/* if above limits, break to queue */
  		if (!tg_may_dispatch(tg, bio, NULL))
  			break;
  
  		/* within limits, let's charge and dispatch directly */

  		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(tg, rw);

  
  		/*
  		 * @bio passed through this layer without being throttled.
  		 * Climb up the ladder.  If we''re already at the top, it
  		 * can be executed directly.
  		 */

  		qn = &tg->qnode_on_parent[rw];

  		sq = sq->parent_sq;
  		tg = sq_to_tg(sq);
  		if (!tg)
  			goto out_unlock;

  	}

  	/* out-of-limit, queue to @tg */

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

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

  		   tg->io_disp[rw], tg->iops[rw],
  		   sq->nr_queued[READ], sq->nr_queued[WRITE]);

  	bio_associate_current(bio);

  	tg->td->nr_queued[rw]++;

  	throtl_add_bio_tg(bio, qn, tg);

  	throttled = true;

  	/*
  	 * Update @tg's dispatch time and force schedule dispatch if @tg
  	 * was empty before @bio.  The forced scheduling isn't likely to
  	 * cause undue delay as @bio is likely to be dispatched directly if
  	 * its @tg's disptime is not in the future.
  	 */

  	if (tg->flags & THROTL_TG_WAS_EMPTY) {

  		tg_update_disptime(tg);

  		throtl_schedule_next_dispatch(tg->service_queue.parent_sq, true);

  	}

  out_unlock:

  	spin_unlock_irq(q->queue_lock);

  out:

  	/*
  	 * As multiple blk-throtls may stack in the same issue path, we
  	 * don't want bios to leave with the flag set.  Clear the flag if
  	 * being issued.
  	 */
  	if (!throttled)
  		bio->bi_rw &= ~REQ_THROTTLED;

  	return throttled;

  }

  /*
   * Dispatch all bios from all children tg's queued on @parent_sq.  On
   * return, @parent_sq is guaranteed to not have any active children tg's
   * and all bios from previously active tg's are on @parent_sq->bio_lists[].
   */
  static void tg_drain_bios(struct throtl_service_queue *parent_sq)
  {
  	struct throtl_grp *tg;
  
  	while ((tg = throtl_rb_first(parent_sq))) {
  		struct throtl_service_queue *sq = &tg->service_queue;
  		struct bio *bio;
  
  		throtl_dequeue_tg(tg);

  		while ((bio = throtl_peek_queued(&sq->queued[READ])))

  			tg_dispatch_one_bio(tg, bio_data_dir(bio));

  		while ((bio = throtl_peek_queued(&sq->queued[WRITE])))

  			tg_dispatch_one_bio(tg, bio_data_dir(bio));
  	}
  }

  /**
   * blk_throtl_drain - drain throttled bios
   * @q: request_queue to drain throttled bios for
   *
   * Dispatch all currently throttled bios on @q through ->make_request_fn().
   */
  void blk_throtl_drain(struct request_queue *q)
  	__releases(q->queue_lock) __acquires(q->queue_lock)
  {
  	struct throtl_data *td = q->td;

  	struct blkcg_gq *blkg;

  	struct cgroup_subsys_state *pos_css;

  	struct bio *bio;

  	int rw;

  	queue_lockdep_assert_held(q);

  	rcu_read_lock();

  	/*
  	 * Drain each tg while doing post-order walk on the blkg tree, so
  	 * that all bios are propagated to td->service_queue.  It'd be
  	 * better to walk service_queue tree directly but blkg walk is
  	 * easier.
  	 */

  	blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg)

  		tg_drain_bios(&blkg_to_tg(blkg)->service_queue);

  	/* finally, transfer bios from top-level tg's into the td */
  	tg_drain_bios(&td->service_queue);
  
  	rcu_read_unlock();

  	spin_unlock_irq(q->queue_lock);

  	/* all bios now should be in td->service_queue, issue them */

  	for (rw = READ; rw <= WRITE; rw++)

  		while ((bio = throtl_pop_queued(&td->service_queue.queued[rw],
  						NULL)))

  			generic_make_request(bio);

  
  	spin_lock_irq(q->queue_lock);
  }

  int blk_throtl_init(struct request_queue *q)
  {
  	struct throtl_data *td;

  	int ret;

  
  	td = kzalloc_node(sizeof(*td), GFP_KERNEL, q->node);
  	if (!td)
  		return -ENOMEM;

  	INIT_WORK(&td->dispatch_work, blk_throtl_dispatch_work_fn);

  	throtl_service_queue_init(&td->service_queue);

  	q->td = td;

  	td->queue = q;

  	/* activate policy */

  	ret = blkcg_activate_policy(q, &blkcg_policy_throtl);

  	if (ret)

  		kfree(td);

  	return ret;

  }
  
  void blk_throtl_exit(struct request_queue *q)
  {

  	BUG_ON(!q->td);

  	throtl_shutdown_wq(q);

  	blkcg_deactivate_policy(q, &blkcg_policy_throtl);

  	kfree(q->td);

  }
  
  static int __init throtl_init(void)
  {

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

  	return blkcg_policy_register(&blkcg_policy_throtl);

  }
  
  module_init(throtl_init);