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blk-throttle.c
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blk-throttle.c
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// SPDX-License-Identifier: GPL-2.0
/*
* Interface for controlling IO bandwidth on a request queue
*
* Copyright (C) 2010 Vivek Goyal <[email protected]>
*/
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <linux/bio.h>
#include <linux/blktrace_api.h>
#include "blk.h"
#include "blk-cgroup-rwstat.h"
#include "blk-stat.h"
#include "blk-throttle.h"
/* Max dispatch from a group in 1 round */
#define THROTL_GRP_QUANTUM 8
/* Total max dispatch from all groups in one round */
#define THROTL_QUANTUM 32
/* Throttling is performed over a slice and after that slice is renewed */
#define DFL_THROTL_SLICE_HD (HZ / 10)
#define DFL_THROTL_SLICE_SSD (HZ / 50)
#define MAX_THROTL_SLICE (HZ)
/* A workqueue to queue throttle related work */
static struct workqueue_struct *kthrotld_workqueue;
#define rb_entry_tg(node) rb_entry((node), struct throtl_grp, rb_node)
/* We measure latency for request size from <= 4k to >= 1M */
#define LATENCY_BUCKET_SIZE 9
struct latency_bucket {
unsigned long total_latency; /* ns / 1024 */
int samples;
};
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];
unsigned int throtl_slice;
/* Work for dispatching throttled bios */
struct work_struct dispatch_work;
bool track_bio_latency;
};
static void throtl_pending_timer_fn(struct timer_list *t);
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 embedded 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);
}
static uint64_t tg_bps_limit(struct throtl_grp *tg, int rw)
{
struct blkcg_gq *blkg = tg_to_blkg(tg);
if (cgroup_subsys_on_dfl(io_cgrp_subsys) && !blkg->parent)
return U64_MAX;
return tg->bps[rw];
}
static unsigned int tg_iops_limit(struct throtl_grp *tg, int rw)
{
struct blkcg_gq *blkg = tg_to_blkg(tg);
if (cgroup_subsys_on_dfl(io_cgrp_subsys) && !blkg->parent)
return UINT_MAX;
return tg->iops[rw];
}
#define request_bucket_index(sectors) \
clamp_t(int, order_base_2(sectors) - 3, 0, LATENCY_BUCKET_SIZE - 1)
/**
* 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)) { \
blk_add_cgroup_trace_msg(__td->queue, \
&tg_to_blkg(__tg)->blkcg->css, "throtl " fmt, ##args);\
} else { \
blk_add_trace_msg(__td->queue, "throtl " fmt, ##args); \
} \
} while (0)
static inline unsigned int throtl_bio_data_size(struct bio *bio)
{
/* assume it's one sector */
if (unlikely(bio_op(bio) == REQ_OP_DISCARD))
return 512;
return bio->bi_iter.bi_size;
}
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;
struct bio *bio;
if (list_empty(queued))
return NULL;
qn = list_first_entry(queued, struct throtl_qnode, node);
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;
struct bio *bio;
if (list_empty(queued))
return NULL;
qn = list_first_entry(queued, struct throtl_qnode, node);
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[READ]);
INIT_LIST_HEAD(&sq->queued[WRITE]);
sq->pending_tree = RB_ROOT_CACHED;
timer_setup(&sq->pending_timer, throtl_pending_timer_fn, 0);
}
static struct blkg_policy_data *throtl_pd_alloc(struct gendisk *disk,
struct blkcg *blkcg, gfp_t gfp)
{
struct throtl_grp *tg;
int rw;
tg = kzalloc_node(sizeof(*tg), gfp, disk->node_id);
if (!tg)
return NULL;
if (blkg_rwstat_init(&tg->stat_bytes, gfp))
goto err_free_tg;
if (blkg_rwstat_init(&tg->stat_ios, gfp))
goto err_exit_stat_bytes;
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] = U64_MAX;
tg->bps[WRITE] = U64_MAX;
tg->iops[READ] = UINT_MAX;
tg->iops[WRITE] = UINT_MAX;
return &tg->pd;
err_exit_stat_bytes:
blkg_rwstat_exit(&tg->stat_bytes);
err_free_tg:
kfree(tg);
return NULL;
}
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 a parent group, summary bps of
* parent group and its subtree groups 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_iops[rw] =
(parent_tg && parent_tg->has_rules_iops[rw]) ||
tg_iops_limit(tg, rw) != UINT_MAX;
tg->has_rules_bps[rw] =
(parent_tg && parent_tg->has_rules_bps[rw]) ||
tg_bps_limit(tg, rw) != U64_MAX;
}
}
static void throtl_pd_online(struct blkg_policy_data *pd)
{
struct throtl_grp *tg = pd_to_tg(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(tg);
}
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);
blkg_rwstat_exit(&tg->stat_bytes);
blkg_rwstat_exit(&tg->stat_ios);
kfree(tg);
}
static struct throtl_grp *
throtl_rb_first(struct throtl_service_queue *parent_sq)
{
struct rb_node *n;
n = rb_first_cached(&parent_sq->pending_tree);
WARN_ON_ONCE(!n);
if (!n)
return NULL;
return rb_entry_tg(n);
}
static void throtl_rb_erase(struct rb_node *n,
struct throtl_service_queue *parent_sq)
{
rb_erase_cached(n, &parent_sq->pending_tree);
RB_CLEAR_NODE(n);
}
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_root.rb_node;
struct rb_node *parent = NULL;
struct throtl_grp *__tg;
unsigned long key = tg->disptime;
bool leftmost = true;
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;
leftmost = false;
}
}
rb_link_node(&tg->rb_node, parent, node);
rb_insert_color_cached(&tg->rb_node, &parent_sq->pending_tree,
leftmost);
}
static void throtl_enqueue_tg(struct throtl_grp *tg)
{
if (!(tg->flags & THROTL_TG_PENDING)) {
tg_service_queue_add(tg);
tg->flags |= THROTL_TG_PENDING;
tg->service_queue.parent_sq->nr_pending++;
}
}
static void throtl_dequeue_tg(struct throtl_grp *tg)
{
if (tg->flags & THROTL_TG_PENDING) {
struct throtl_service_queue *parent_sq =
tg->service_queue.parent_sq;
throtl_rb_erase(&tg->rb_node, parent_sq);
--parent_sq->nr_pending;
tg->flags &= ~THROTL_TG_PENDING;
}
}
/* Call with queue lock held */
static void throtl_schedule_pending_timer(struct throtl_service_queue *sq,
unsigned long expires)
{
unsigned long max_expire = jiffies + 8 * sq_to_td(sq)->throtl_slice;
/*
* Since we are adjusting the throttle limit dynamically, the sleep
* time calculated according to previous limit might be invalid. It's
* possible the cgroup sleep time is very long and no other cgroups
* have IO running so notify the limit changes. Make sure the cgroup
* doesn't sleep too long to avoid the missed notification.
*/
if (time_after(expires, max_expire))
expires = max_expire;
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;
tg->carryover_bytes[rw] = 0;
tg->carryover_ios[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(start, tg->slice_start[rw]))
tg->slice_start[rw] = start;
tg->slice_end[rw] = jiffies + tg->td->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,
bool clear_carryover)
{
tg->bytes_disp[rw] = 0;
tg->io_disp[rw] = 0;
tg->slice_start[rw] = jiffies;
tg->slice_end[rw] = jiffies + tg->td->throtl_slice;
if (clear_carryover) {
tg->carryover_bytes[rw] = 0;
tg->carryover_ios[rw] = 0;
}
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, tg->td->throtl_slice);
}
static inline void throtl_extend_slice(struct throtl_grp *tg, bool rw,
unsigned long jiffy_end)
{
throtl_set_slice_end(tg, rw, jiffy_end);
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 true;
}
static unsigned int calculate_io_allowed(u32 iops_limit,
unsigned long jiffy_elapsed)
{
unsigned int io_allowed;
u64 tmp;
/*
* jiffy_elapsed 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)iops_limit * jiffy_elapsed;
do_div(tmp, HZ);
if (tmp > UINT_MAX)
io_allowed = UINT_MAX;
else
io_allowed = tmp;
return io_allowed;
}
static u64 calculate_bytes_allowed(u64 bps_limit, unsigned long jiffy_elapsed)
{
/*
* Can result be wider than 64 bits?
* We check against 62, not 64, due to ilog2 truncation.
*/
if (ilog2(bps_limit) + ilog2(jiffy_elapsed) - ilog2(HZ) > 62)
return U64_MAX;
return mul_u64_u64_div_u64(bps_limit, (u64)jiffy_elapsed, (u64)HZ);
}
/* Trim the used slices and adjust slice start accordingly */
static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw)
{
unsigned long time_elapsed;
long long bytes_trim;
int io_trim;
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 dispatched
* 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 + tg->td->throtl_slice);
time_elapsed = rounddown(jiffies - tg->slice_start[rw],
tg->td->throtl_slice);
if (!time_elapsed)
return;
bytes_trim = calculate_bytes_allowed(tg_bps_limit(tg, rw),
time_elapsed) +
tg->carryover_bytes[rw];
io_trim = calculate_io_allowed(tg_iops_limit(tg, rw), time_elapsed) +
tg->carryover_ios[rw];
if (bytes_trim <= 0 && io_trim <= 0)
return;
tg->carryover_bytes[rw] = 0;
if ((long long)tg->bytes_disp[rw] >= bytes_trim)
tg->bytes_disp[rw] -= bytes_trim;
else
tg->bytes_disp[rw] = 0;
tg->carryover_ios[rw] = 0;
if ((int)tg->io_disp[rw] >= io_trim)
tg->io_disp[rw] -= io_trim;
else
tg->io_disp[rw] = 0;
tg->slice_start[rw] += time_elapsed;
throtl_log(&tg->service_queue,
"[%c] trim slice nr=%lu bytes=%lld io=%d start=%lu end=%lu jiffies=%lu",
rw == READ ? 'R' : 'W', time_elapsed / tg->td->throtl_slice,
bytes_trim, io_trim, tg->slice_start[rw], tg->slice_end[rw],
jiffies);
}
static void __tg_update_carryover(struct throtl_grp *tg, bool rw)
{
unsigned long jiffy_elapsed = jiffies - tg->slice_start[rw];
u64 bps_limit = tg_bps_limit(tg, rw);
u32 iops_limit = tg_iops_limit(tg, rw);
/*
* If config is updated while bios are still throttled, calculate and
* accumulate how many bytes/ios are waited across changes. And
* carryover_bytes/ios will be used to calculate new wait time under new
* configuration.
*/
if (bps_limit != U64_MAX)
tg->carryover_bytes[rw] +=
calculate_bytes_allowed(bps_limit, jiffy_elapsed) -
tg->bytes_disp[rw];
if (iops_limit != UINT_MAX)
tg->carryover_ios[rw] +=
calculate_io_allowed(iops_limit, jiffy_elapsed) -
tg->io_disp[rw];
}
static void tg_update_carryover(struct throtl_grp *tg)
{
if (tg->service_queue.nr_queued[READ])
__tg_update_carryover(tg, READ);
if (tg->service_queue.nr_queued[WRITE])
__tg_update_carryover(tg, WRITE);
/* see comments in struct throtl_grp for meaning of these fields. */
throtl_log(&tg->service_queue, "%s: %lld %lld %d %d\n", __func__,
tg->carryover_bytes[READ], tg->carryover_bytes[WRITE],
tg->carryover_ios[READ], tg->carryover_ios[WRITE]);
}
static unsigned long tg_within_iops_limit(struct throtl_grp *tg, struct bio *bio,
u32 iops_limit)
{
bool rw = bio_data_dir(bio);
int io_allowed;
unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
if (iops_limit == UINT_MAX) {
return 0;
}
jiffy_elapsed = jiffies - tg->slice_start[rw];
/* Round up to the next throttle slice, wait time must be nonzero */
jiffy_elapsed_rnd = roundup(jiffy_elapsed + 1, tg->td->throtl_slice);
io_allowed = calculate_io_allowed(iops_limit, jiffy_elapsed_rnd) +
tg->carryover_ios[rw];
if (io_allowed > 0 && tg->io_disp[rw] + 1 <= io_allowed)
return 0;
/* Calc approx time to dispatch */
jiffy_wait = jiffy_elapsed_rnd - jiffy_elapsed;
return jiffy_wait;
}
static unsigned long tg_within_bps_limit(struct throtl_grp *tg, struct bio *bio,
u64 bps_limit)
{
bool rw = bio_data_dir(bio);
long long bytes_allowed;
u64 extra_bytes;
unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
unsigned int bio_size = throtl_bio_data_size(bio);
/* no need to throttle if this bio's bytes have been accounted */
if (bps_limit == U64_MAX || bio_flagged(bio, BIO_BPS_THROTTLED)) {
return 0;
}
jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
/* Slice has just started. Consider one slice interval */
if (!jiffy_elapsed)
jiffy_elapsed_rnd = tg->td->throtl_slice;
jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, tg->td->throtl_slice);
bytes_allowed = calculate_bytes_allowed(bps_limit, jiffy_elapsed_rnd) +
tg->carryover_bytes[rw];
if (bytes_allowed > 0 && tg->bytes_disp[rw] + bio_size <= bytes_allowed)
return 0;
/* Calc approx time to dispatch */
extra_bytes = tg->bytes_disp[rw] + bio_size - bytes_allowed;
jiffy_wait = div64_u64(extra_bytes * HZ, bps_limit);
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);
return jiffy_wait;
}
/*
* 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;
u64 bps_limit = tg_bps_limit(tg, rw);
u32 iops_limit = tg_iops_limit(tg, rw);
/*
* 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 ((bps_limit == U64_MAX && iops_limit == UINT_MAX) ||
tg->flags & THROTL_TG_CANCELING) {
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. New slice is started only for empty throttle group.
* If there is queued bio, that means there should be an active
* slice and it should be extended instead.
*/
if (throtl_slice_used(tg, rw) && !(tg->service_queue.nr_queued[rw]))
throtl_start_new_slice(tg, rw, true);
else {
if (time_before(tg->slice_end[rw],
jiffies + tg->td->throtl_slice))
throtl_extend_slice(tg, rw,
jiffies + tg->td->throtl_slice);
}
bps_wait = tg_within_bps_limit(tg, bio, bps_limit);
iops_wait = tg_within_iops_limit(tg, bio, iops_limit);
if (bps_wait + iops_wait == 0) {
if (wait)
*wait = 0;
return true;
}
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 false;
}
static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio)
{
bool rw = bio_data_dir(bio);
unsigned int bio_size = throtl_bio_data_size(bio);
/* Charge the bio to the group */
if (!bio_flagged(bio, BIO_BPS_THROTTLED)) {
tg->bytes_disp[rw] += bio_size;
tg->last_bytes_disp[rw] += bio_size;
}
tg->io_disp[rw]++;
tg->last_io_disp[rw]++;
}
/**
* 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
* cleared 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;
bio = throtl_peek_queued(&sq->queued[READ]);
if (bio)
tg_may_dispatch(tg, bio, &read_wait);
bio = throtl_peek_queued(&sq->queued[WRITE]);
if (bio)
tg_may_dispatch(tg, bio, &write_wait);
min_wait = min(read_wait, write_wait);
disptime = jiffies + min_wait;
/* Update dispatch time */
throtl_rb_erase(&tg->rb_node, tg->service_queue.parent_sq);
tg->disptime = disptime;
tg_service_queue_add(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 {
bio_set_flag(bio, BIO_BPS_THROTTLED);
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, READ);
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, WRITE);
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;
struct throtl_service_queue *sq;
if (!parent_sq->nr_pending)
break;
tg = throtl_rb_first(parent_sq);
if (!tg)
break;
if (time_before(jiffies, tg->disptime))
break;
nr_disp += throtl_dispatch_tg(tg);
sq = &tg->service_queue;
if (sq->nr_queued[READ] || sq->nr_queued[WRITE])
tg_update_disptime(tg);
else
throtl_dequeue_tg(tg);