blk-throttle.c 30.1 KB
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/*
 * 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 */

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/* 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);

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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];

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

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	/* Number of bytes disptached in current slice */
	uint64_t bytes_disp[2];
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	/* Number of bio's dispatched in current slice */
	unsigned int io_disp[2];
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	/* When did we start a new slice */
	unsigned long slice_start[2];
	unsigned long slice_end[2];
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	/* Some throttle limits got updated for the group */
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	int limits_changed;
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};

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;

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	struct throtl_grp *root_tg;
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	struct request_queue *queue;

	/* Total Number of queued bios on READ and WRITE lists */
	unsigned int nr_queued[2];

	/*
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Vivek Goyal 已提交
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	 * number of total undestroyed groups
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	 */
	unsigned int nr_undestroyed_grps;

	/* Work for dispatching throttled bios */
	struct delayed_work throtl_work;
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	int limits_changed;
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};

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);
}

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static void throtl_init_group(struct throtl_grp *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]);
	tg->limits_changed = false;

	/* Practically unlimited BW */
	tg->bps[0] = tg->bps[1] = -1;
	tg->iops[0] = tg->iops[1] = -1;

	/*
	 * 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);
}

/* Should be called with rcu read lock held (needed for blkcg) */
static void
throtl_add_group_to_td_list(struct throtl_data *td, struct throtl_grp *tg)
{
	hlist_add_head(&tg->tg_node, &td->tg_list);
	td->nr_undestroyed_grps++;
}

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static void throtl_init_add_tg_lists(struct throtl_data *td,
			struct throtl_grp *tg, struct blkio_cgroup *blkcg)
{
	struct backing_dev_info *bdi = &td->queue->backing_dev_info;
	unsigned int major, minor;

	/* 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);

	throtl_add_group_to_td_list(td, tg);
}

/* Should be called without queue lock and outside of rcu period */
static struct throtl_grp *throtl_alloc_tg(struct throtl_data *td)
{
	struct throtl_grp *tg = NULL;

	tg = kzalloc_node(sizeof(*tg), GFP_ATOMIC, td->queue->node);
	if (!tg)
		return NULL;

	throtl_init_group(tg);
	return tg;
}

static struct
throtl_grp *throtl_find_tg(struct throtl_data *td, struct blkio_cgroup *blkcg)
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{
	struct throtl_grp *tg = NULL;
	void *key = td;
	struct backing_dev_info *bdi = &td->queue->backing_dev_info;
	unsigned int major, minor;

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

	return tg;
}

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/*
 * This function returns with queue lock unlocked in case of error, like
 * request queue is no more
 */
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static struct throtl_grp * throtl_get_tg(struct throtl_data *td)
{
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	struct throtl_grp *tg = NULL, *__tg = NULL;
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	struct blkio_cgroup *blkcg;
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	struct request_queue *q = td->queue;
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	rcu_read_lock();
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	blkcg = task_blkio_cgroup(current);
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	tg = throtl_find_tg(td, blkcg);
	if (tg) {
		rcu_read_unlock();
		return tg;
	}

	/*
	 * 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
	 *
	 * Take the request queue reference to make sure queue does not
	 * go away once we return from allocation.
	 */
	blk_get_queue(q);
	rcu_read_unlock();
	spin_unlock_irq(q->queue_lock);

	tg = throtl_alloc_tg(td);
	/*
	 * We might have slept in group allocation. Make sure queue is not
	 * dead
	 */
	if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags))) {
		blk_put_queue(q);
		if (tg)
			kfree(tg);

		return ERR_PTR(-ENODEV);
	}
	blk_put_queue(q);

	/* Group allocated and queue is still alive. take the lock */
	spin_lock_irq(q->queue_lock);

	/*
	 * Initialize the new group. After sleeping, read the blkcg again.
	 */
	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
	 */
	__tg = throtl_find_tg(td, blkcg);

	if (__tg) {
		kfree(tg);
		rcu_read_unlock();
		return __tg;
	}

	/* Group allocation failed. Account the IO to root group */
	if (!tg) {
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		tg = td->root_tg;
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		return tg;
	}

	throtl_init_add_tg_lists(td, tg, blkcg);
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	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))
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		throtl_schedule_delayed_work(td, 0);
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	else
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		throtl_schedule_delayed_work(td, (st->min_disptime - jiffies));
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}

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

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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);
}

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

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	/*
	 * 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);

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	time_elapsed = jiffies - tg->slice_start[rw];

	nr_slices = time_elapsed / throtl_slice;

	if (!nr_slices)
		return;
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	tmp = tg->bps[rw] * throtl_slice * nr_slices;
	do_div(tmp, HZ);
	bytes_trim = tmp;
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	io_trim = (tg->iops[rw] * throtl_slice * nr_slices)/HZ;
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	if (!bytes_trim && !io_trim)
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		return;

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

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

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

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	throtl_log_tg(td, tg, "[%c] trim slice nr=%lu bytes=%llu io=%lu"
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			" start=%lu end=%lu jiffies=%lu",
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			rw == READ ? 'R' : 'W', nr_slices, bytes_trim, io_trim,
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			tg->slice_start[rw], tg->slice_end[rw], jiffies);
}

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static bool tg_with_in_iops_limit(struct throtl_data *td, struct throtl_grp *tg,
		struct bio *bio, unsigned long *wait)
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{
	bool rw = bio_data_dir(bio);
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	unsigned int io_allowed;
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	unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
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	u64 tmp;
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	jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
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	/* 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);

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	/*
	 * 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;
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	if (tg->io_disp[rw] + 1 <= io_allowed) {
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		if (wait)
			*wait = 0;
		return 1;
	}

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	/* 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);
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	u64 bytes_allowed, extra_bytes, tmp;
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	unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
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	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);

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	tmp = tg->bps[rw] * jiffy_elapsed_rnd;
	do_div(tmp, HZ);
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	bytes_allowed = tmp;
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	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;
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	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]));
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	/* 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);
680 681 682 683 684 685 686 687 688 689 690

	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;
691
	tg->io_disp[rw]++;
692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757

	/*
	 * 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;
758
	unsigned int max_nr_writes = throtl_grp_quantum - max_nr_reads;
759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816
	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;
}

817 818 819 820 821
static void throtl_process_limit_change(struct throtl_data *td)
{
	struct throtl_grp *tg;
	struct hlist_node *pos, *n;

822
	if (!td->limits_changed)
823 824
		return;

825
	xchg(&td->limits_changed, false);
826

827
	throtl_log(td, "limits changed");
828

829
	hlist_for_each_entry_safe(tg, pos, n, &td->tg_list, tg_node) {
830 831 832 833 834 835 836 837 838 839
		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]);

840 841 842 843 844 845 846 847 848
		/*
		 * 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);

849
		if (throtl_tg_on_rr(tg))
850 851 852 853
			tg_update_disptime(td, tg);
	}
}

854 855 856 857 858 859 860
/* 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;
861
	struct blk_plug plug;
862 863 864

	spin_lock_irq(q->queue_lock);

865 866
	throtl_process_limit_change(td);

867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889
	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) {
890
		blk_start_plug(&plug);
891 892
		while((bio = bio_list_pop(&bio_list_on_stack)))
			generic_make_request(bio);
893
		blk_finish_plug(&plug);
894 895 896 897 898 899 900 901 902 903 904 905 906 907
	}
	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 */
908 909
static void
throtl_schedule_delayed_work(struct throtl_data *td, unsigned long delay)
910 911 912 913
{

	struct delayed_work *dwork = &td->throtl_work;

914 915
	/* schedule work if limits changed even if no bio is queued */
	if (total_nr_queued(td) > 0 || td->limits_changed) {
916 917 918 919 920
		/*
		 * We might have a work scheduled to be executed in future.
		 * Cancel that and schedule a new one.
		 */
		__cancel_delayed_work(dwork);
921
		queue_delayed_work(kthrotld_workqueue, dwork, delay);
922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987
		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);
}

988 989 990 991 992 993 994 995 996
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);
}

997 998 999
/*
 * For all update functions, key should be a valid pointer because these
 * update functions are called under blkcg_lock, that means, blkg is
L
Lucas De Marchi 已提交
1000
 * valid and in turn key is valid. queue exit path can not race because
1001 1002 1003 1004 1005 1006 1007
 * 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)
1008
{
1009
	struct throtl_data *td = key;
1010
	struct throtl_grp *tg = tg_of_blkg(blkg);
1011

1012 1013
	tg->bps[READ] = read_bps;
	throtl_update_blkio_group_common(td, tg);
1014 1015
}

1016 1017
static void throtl_update_blkio_group_write_bps(void *key,
				struct blkio_group *blkg, u64 write_bps)
1018
{
1019
	struct throtl_data *td = key;
1020
	struct throtl_grp *tg = tg_of_blkg(blkg);
1021

1022 1023
	tg->bps[WRITE] = write_bps;
	throtl_update_blkio_group_common(td, tg);
1024 1025
}

1026 1027
static void throtl_update_blkio_group_read_iops(void *key,
			struct blkio_group *blkg, unsigned int read_iops)
1028
{
1029
	struct throtl_data *td = key;
1030
	struct throtl_grp *tg = tg_of_blkg(blkg);
1031

1032 1033
	tg->iops[READ] = read_iops;
	throtl_update_blkio_group_common(td, tg);
1034 1035
}

1036 1037
static void throtl_update_blkio_group_write_iops(void *key,
			struct blkio_group *blkg, unsigned int write_iops)
1038
{
1039
	struct throtl_data *td = key;
1040
	struct throtl_grp *tg = tg_of_blkg(blkg);
1041

1042 1043
	tg->iops[WRITE] = write_iops;
	throtl_update_blkio_group_common(td, tg);
1044 1045
}

1046
static void throtl_shutdown_wq(struct request_queue *q)
1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059
{
	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,
1060 1061 1062 1063
		.blkio_update_group_read_iops_fn =
					throtl_update_blkio_group_read_iops,
		.blkio_update_group_write_iops_fn =
					throtl_update_blkio_group_write_iops,
1064
	},
1065
	.plid = BLKIO_POLICY_THROTL,
1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082
};

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);

1083 1084 1085 1086 1087 1088 1089 1090 1091
	if (IS_ERR(tg)) {
		if (PTR_ERR(tg)	== -ENODEV) {
			/*
			 * Queue is gone. No queue lock held here.
			 */
			return -ENODEV;
		}
	}

1092 1093 1094 1095 1096
	if (tg->nr_queued[rw]) {
		/*
		 * There is already another bio queued in same dir. No
		 * need to update dispatch time.
		 */
1097
		update_disptime = false;
1098
		goto queue_bio;
1099

1100 1101 1102 1103 1104
	}

	/* Bio is with-in rate limit of group */
	if (tg_may_dispatch(td, tg, bio, NULL)) {
		throtl_charge_bio(tg, bio);
1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117

		/*
		 * 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);
1118 1119 1120 1121
		goto out;
	}

queue_bio:
1122 1123 1124
	throtl_log_tg(td, tg, "[%c] bio. bdisp=%u sz=%u bps=%llu"
			" iodisp=%u iops=%u queued=%d/%d",
			rw == READ ? 'R' : 'W',
1125
			tg->bytes_disp[rw], bio->bi_size, tg->bps[rw],
1126
			tg->io_disp[rw], tg->iops[rw],
1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152
			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;
1153
	td->limits_changed = false;
1154
	INIT_DELAYED_WORK(&td->throtl_work, blk_throtl_work);
1155

1156 1157 1158
	/* alloc and Init root group. */
	td->queue = q;
	tg = throtl_alloc_tg(td);
V
Vivek Goyal 已提交
1159

1160 1161 1162 1163 1164 1165
	if (!tg) {
		kfree(td);
		return -ENOMEM;
	}

	td->root_tg = tg;
1166 1167 1168 1169 1170

	rcu_read_lock();
	blkiocg_add_blkio_group(&blkio_root_cgroup, &tg->blkg, (void *)td,
					0, BLKIO_POLICY_THROTL);
	rcu_read_unlock();
1171
	throtl_add_group_to_td_list(td, tg);
1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184

	/* Attach throtl data to request queue */
	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);

1185
	throtl_shutdown_wq(q);
1186 1187 1188 1189 1190

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

	/* If there are other groups */
V
Vivek Goyal 已提交
1191
	if (td->nr_undestroyed_grps > 0)
1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208
		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();
1209 1210 1211 1212 1213 1214

	/*
	 * Just being safe to make sure after previous flush if some body did
	 * update limits through cgroup and another work got queued, cancel
	 * it.
	 */
1215
	throtl_shutdown_wq(q);
1216 1217 1218 1219 1220
	throtl_td_free(td);
}

static int __init throtl_init(void)
{
1221 1222 1223 1224
	kthrotld_workqueue = alloc_workqueue("kthrotld", WQ_MEM_RECLAIM, 0);
	if (!kthrotld_workqueue)
		panic("Failed to create kthrotld\n");

1225 1226 1227 1228 1229
	blkio_policy_register(&blkio_policy_throtl);
	return 0;
}

module_init(throtl_init);