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linux-next/block/blk-throttle.c
Vivek Goyal 04a6b516cd blk-throttle: Correct the placement of smp_rmb() 
o I was discussing what are the variable being updated without spin lock and
  why do we need barriers and Oleg pointed out that location of smp_rmb()
  should be between read of td->limits_changed and tg->limits_changed. This
  patch fixes it.

o Following is one possible sequence of events. Say cpu0 is executing
  throtl_update_blkio_group_read_bps() and cpu1 is executing
  throtl_process_limit_change().

 cpu0                                                cpu1

 tg->limits_changed = true;
 smp_mb__before_atomic_inc();
 atomic_inc(&td->limits_changed);

                                     if (!atomic_read(&td->limits_changed))
                                             return;

                                     if (tg->limits_changed)
                                             do_something;

 If cpu0 has updated tg->limits_changed and td->limits_changed, we want to
 make sure that if update to td->limits_changed is visible on cpu1, then
 update to tg->limits_changed should also be visible.

 Oleg pointed out to ensure that we need to insert an smp_rmb() between
 td->limits_changed read and tg->limits_changed read.

o I had erroneously put smp_rmb() before atomic_read(&td->limits_changed).
  This patch fixes it.

Reported-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-12-01 19:34:52 +01:00

1135 lines
28 KiB
C
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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 */
struct throtl_rb_root {
struct rb_root rb;
struct rb_node *left;
unsigned int count;
unsigned long min_disptime;
};
#define THROTL_RB_ROOT (struct throtl_rb_root) { .rb = RB_ROOT, .left = NULL, \
.count = 0, .min_disptime = 0}
#define rb_entry_tg(node) rb_entry((node), struct throtl_grp, rb_node)
struct throtl_grp {
/* List of throtl groups on the request queue*/
struct hlist_node tg_node;
/* active throtl group service_tree member */
struct rb_node rb_node;
/*
* Dispatch time in jiffies. This is the estimated time when group
* will unthrottle and is ready to dispatch more bio. It is used as
* key to sort active groups in service tree.
*/
unsigned long disptime;
struct blkio_group blkg;
atomic_t ref;
unsigned int flags;
/* Two lists for READ and WRITE */
struct bio_list bio_lists[2];
/* Number of queued bios on READ and WRITE lists */
unsigned int nr_queued[2];
/* bytes per second rate limits */
uint64_t bps[2];
/* IOPS limits */
unsigned int iops[2];
/* Number of bytes disptached in current slice */
uint64_t bytes_disp[2];
/* Number of bio's dispatched in current slice */
unsigned int io_disp[2];
/* When did we start a new slice */
unsigned long slice_start[2];
unsigned long slice_end[2];
/* Some throttle limits got updated for the group */
bool limits_changed;
};
struct throtl_data
{
/* List of throtl groups */
struct hlist_head tg_list;
/* service tree for active throtl groups */
struct throtl_rb_root tg_service_tree;
struct throtl_grp root_tg;
struct request_queue *queue;
/* Total Number of queued bios on READ and WRITE lists */
unsigned int nr_queued[2];
/*
* number of total undestroyed groups
*/
unsigned int nr_undestroyed_grps;
/* Work for dispatching throttled bios */
struct delayed_work throtl_work;
atomic_t limits_changed;
};
enum tg_state_flags {
THROTL_TG_FLAG_on_rr = 0, /* on round-robin busy list */
};
#define THROTL_TG_FNS(name) \
static inline void throtl_mark_tg_##name(struct throtl_grp *tg) \
{ \
(tg)->flags |= (1 << THROTL_TG_FLAG_##name); \
} \
static inline void throtl_clear_tg_##name(struct throtl_grp *tg) \
{ \
(tg)->flags &= ~(1 << THROTL_TG_FLAG_##name); \
} \
static inline int throtl_tg_##name(const struct throtl_grp *tg) \
{ \
return ((tg)->flags & (1 << THROTL_TG_FLAG_##name)) != 0; \
}
THROTL_TG_FNS(on_rr);
#define throtl_log_tg(td, tg, fmt, args...) \
blk_add_trace_msg((td)->queue, "throtl %s " fmt, \
blkg_path(&(tg)->blkg), ##args); \
#define throtl_log(td, fmt, args...) \
blk_add_trace_msg((td)->queue, "throtl " fmt, ##args)
static inline struct throtl_grp *tg_of_blkg(struct blkio_group *blkg)
{
if (blkg)
return container_of(blkg, struct throtl_grp, blkg);
return NULL;
}
static inline int total_nr_queued(struct throtl_data *td)
{
return (td->nr_queued[0] + td->nr_queued[1]);
}
static inline struct throtl_grp *throtl_ref_get_tg(struct throtl_grp *tg)
{
atomic_inc(&tg->ref);
return tg;
}
static void throtl_put_tg(struct throtl_grp *tg)
{
BUG_ON(atomic_read(&tg->ref) <= 0);
if (!atomic_dec_and_test(&tg->ref))
return;
kfree(tg);
}
static struct throtl_grp * throtl_find_alloc_tg(struct throtl_data *td,
struct cgroup *cgroup)
{
struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);
struct throtl_grp *tg = NULL;
void *key = td;
struct backing_dev_info *bdi = &td->queue->backing_dev_info;
unsigned int major, minor;
/*
* TODO: Speed up blkiocg_lookup_group() by maintaining a radix
* tree of blkg (instead of traversing through hash list all
* the time.
*/
tg = tg_of_blkg(blkiocg_lookup_group(blkcg, key));
/* Fill in device details for root group */
if (tg && !tg->blkg.dev && bdi->dev && dev_name(bdi->dev)) {
sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
tg->blkg.dev = MKDEV(major, minor);
goto done;
}
if (tg)
goto done;
tg = kzalloc_node(sizeof(*tg), GFP_ATOMIC, td->queue->node);
if (!tg)
goto done;
INIT_HLIST_NODE(&tg->tg_node);
RB_CLEAR_NODE(&tg->rb_node);
bio_list_init(&tg->bio_lists[0]);
bio_list_init(&tg->bio_lists[1]);
/*
* Take the initial reference that will be released on destroy
* This can be thought of a joint reference by cgroup and
* request queue which will be dropped by either request queue
* exit or cgroup deletion path depending on who is exiting first.
*/
atomic_set(&tg->ref, 1);
/* Add group onto cgroup list */
sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
blkiocg_add_blkio_group(blkcg, &tg->blkg, (void *)td,
MKDEV(major, minor), BLKIO_POLICY_THROTL);
tg->bps[READ] = blkcg_get_read_bps(blkcg, tg->blkg.dev);
tg->bps[WRITE] = blkcg_get_write_bps(blkcg, tg->blkg.dev);
tg->iops[READ] = blkcg_get_read_iops(blkcg, tg->blkg.dev);
tg->iops[WRITE] = blkcg_get_write_iops(blkcg, tg->blkg.dev);
hlist_add_head(&tg->tg_node, &td->tg_list);
td->nr_undestroyed_grps++;
done:
return tg;
}
static struct throtl_grp * throtl_get_tg(struct throtl_data *td)
{
struct cgroup *cgroup;
struct throtl_grp *tg = NULL;
rcu_read_lock();
cgroup = task_cgroup(current, blkio_subsys_id);
tg = throtl_find_alloc_tg(td, cgroup);
if (!tg)
tg = &td->root_tg;
rcu_read_unlock();
return tg;
}
static struct throtl_grp *throtl_rb_first(struct throtl_rb_root *root)
{
/* Service tree is empty */
if (!root->count)
return NULL;
if (!root->left)
root->left = rb_first(&root->rb);
if (root->left)
return rb_entry_tg(root->left);
return NULL;
}
static void rb_erase_init(struct rb_node *n, struct rb_root *root)
{
rb_erase(n, root);
RB_CLEAR_NODE(n);
}
static void throtl_rb_erase(struct rb_node *n, struct throtl_rb_root *root)
{
if (root->left == n)
root->left = NULL;
rb_erase_init(n, &root->rb);
--root->count;
}
static void update_min_dispatch_time(struct throtl_rb_root *st)
{
struct throtl_grp *tg;
tg = throtl_rb_first(st);
if (!tg)
return;
st->min_disptime = tg->disptime;
}
static void
tg_service_tree_add(struct throtl_rb_root *st, struct throtl_grp *tg)
{
struct rb_node **node = &st->rb.rb_node;
struct rb_node *parent = NULL;
struct throtl_grp *__tg;
unsigned long key = tg->disptime;
int left = 1;
while (*node != NULL) {
parent = *node;
__tg = rb_entry_tg(parent);
if (time_before(key, __tg->disptime))
node = &parent->rb_left;
else {
node = &parent->rb_right;
left = 0;
}
}
if (left)
st->left = &tg->rb_node;
rb_link_node(&tg->rb_node, parent, node);
rb_insert_color(&tg->rb_node, &st->rb);
}
static void __throtl_enqueue_tg(struct throtl_data *td, struct throtl_grp *tg)
{
struct throtl_rb_root *st = &td->tg_service_tree;
tg_service_tree_add(st, tg);
throtl_mark_tg_on_rr(tg);
st->count++;
}
static void throtl_enqueue_tg(struct throtl_data *td, struct throtl_grp *tg)
{
if (!throtl_tg_on_rr(tg))
__throtl_enqueue_tg(td, tg);
}
static void __throtl_dequeue_tg(struct throtl_data *td, struct throtl_grp *tg)
{
throtl_rb_erase(&tg->rb_node, &td->tg_service_tree);
throtl_clear_tg_on_rr(tg);
}
static void throtl_dequeue_tg(struct throtl_data *td, struct throtl_grp *tg)
{
if (throtl_tg_on_rr(tg))
__throtl_dequeue_tg(td, tg);
}
static void throtl_schedule_next_dispatch(struct throtl_data *td)
{
struct throtl_rb_root *st = &td->tg_service_tree;
/*
* If there are more bios pending, schedule more work.
*/
if (!total_nr_queued(td))
return;
BUG_ON(!st->count);
update_min_dispatch_time(st);
if (time_before_eq(st->min_disptime, jiffies))
throtl_schedule_delayed_work(td->queue, 0);
else
throtl_schedule_delayed_work(td->queue,
(st->min_disptime - jiffies));
}
static inline void
throtl_start_new_slice(struct throtl_data *td, struct throtl_grp *tg, bool rw)
{
tg->bytes_disp[rw] = 0;
tg->io_disp[rw] = 0;
tg->slice_start[rw] = jiffies;
tg->slice_end[rw] = jiffies + throtl_slice;
throtl_log_tg(td, tg, "[%c] new slice start=%lu end=%lu jiffies=%lu",
rw == READ ? 'R' : 'W', tg->slice_start[rw],
tg->slice_end[rw], jiffies);
}
static inline void throtl_set_slice_end(struct throtl_data *td,
struct throtl_grp *tg, bool rw, unsigned long jiffy_end)
{
tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
}
static inline void throtl_extend_slice(struct throtl_data *td,
struct throtl_grp *tg, bool rw, unsigned long jiffy_end)
{
tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
throtl_log_tg(td, tg, "[%c] extend slice start=%lu end=%lu jiffies=%lu",
rw == READ ? 'R' : 'W', tg->slice_start[rw],
tg->slice_end[rw], jiffies);
}
/* Determine if previously allocated or extended slice is complete or not */
static bool
throtl_slice_used(struct throtl_data *td, struct throtl_grp *tg, bool rw)
{
if (time_in_range(jiffies, tg->slice_start[rw], tg->slice_end[rw]))
return 0;
return 1;
}
/* Trim the used slices and adjust slice start accordingly */
static inline void
throtl_trim_slice(struct throtl_data *td, struct throtl_grp *tg, bool rw)
{
unsigned long nr_slices, time_elapsed, io_trim;
u64 bytes_trim, tmp;
BUG_ON(time_before(tg->slice_end[rw], tg->slice_start[rw]));
/*
* If bps are unlimited (-1), then time slice don't get
* renewed. Don't try to trim the slice if slice is used. A new
* slice will start when appropriate.
*/
if (throtl_slice_used(td, tg, rw))
return;
/*
* A bio has been dispatched. Also adjust slice_end. It might happen
* that initially cgroup limit was very low resulting in high
* slice_end, but later limit was bumped up and bio was dispached
* sooner, then we need to reduce slice_end. A high bogus slice_end
* is bad because it does not allow new slice to start.
*/
throtl_set_slice_end(td, tg, rw, jiffies + throtl_slice);
time_elapsed = jiffies - tg->slice_start[rw];
nr_slices = time_elapsed / throtl_slice;
if (!nr_slices)
return;
tmp = tg->bps[rw] * throtl_slice * nr_slices;
do_div(tmp, HZ);
bytes_trim = tmp;
io_trim = (tg->iops[rw] * throtl_slice * nr_slices)/HZ;
if (!bytes_trim && !io_trim)
return;
if (tg->bytes_disp[rw] >= bytes_trim)
tg->bytes_disp[rw] -= bytes_trim;
else
tg->bytes_disp[rw] = 0;
if (tg->io_disp[rw] >= io_trim)
tg->io_disp[rw] -= io_trim;
else
tg->io_disp[rw] = 0;
tg->slice_start[rw] += nr_slices * throtl_slice;
throtl_log_tg(td, tg, "[%c] trim slice nr=%lu bytes=%llu io=%lu"
" start=%lu end=%lu jiffies=%lu",
rw == READ ? 'R' : 'W', nr_slices, bytes_trim, io_trim,
tg->slice_start[rw], tg->slice_end[rw], jiffies);
}
static bool tg_with_in_iops_limit(struct throtl_data *td, struct throtl_grp *tg,
struct bio *bio, unsigned long *wait)
{
bool rw = bio_data_dir(bio);
unsigned int io_allowed;
unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
u64 tmp;
jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
/* Slice has just started. Consider one slice interval */
if (!jiffy_elapsed)
jiffy_elapsed_rnd = throtl_slice;
jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);
/*
* jiffy_elapsed_rnd should not be a big value as minimum iops can be
* 1 then at max jiffy elapsed should be equivalent of 1 second as we
* will allow dispatch after 1 second and after that slice should
* have been trimmed.
*/
tmp = (u64)tg->iops[rw] * jiffy_elapsed_rnd;
do_div(tmp, HZ);
if (tmp > UINT_MAX)
io_allowed = UINT_MAX;
else
io_allowed = tmp;
if (tg->io_disp[rw] + 1 <= io_allowed) {
if (wait)
*wait = 0;
return 1;
}
/* Calc approx time to dispatch */
jiffy_wait = ((tg->io_disp[rw] + 1) * HZ)/tg->iops[rw] + 1;
if (jiffy_wait > jiffy_elapsed)
jiffy_wait = jiffy_wait - jiffy_elapsed;
else
jiffy_wait = 1;
if (wait)
*wait = jiffy_wait;
return 0;
}
static bool tg_with_in_bps_limit(struct throtl_data *td, struct throtl_grp *tg,
struct bio *bio, unsigned long *wait)
{
bool rw = bio_data_dir(bio);
u64 bytes_allowed, extra_bytes, tmp;
unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
/* Slice has just started. Consider one slice interval */
if (!jiffy_elapsed)
jiffy_elapsed_rnd = throtl_slice;
jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);
tmp = tg->bps[rw] * jiffy_elapsed_rnd;
do_div(tmp, HZ);
bytes_allowed = tmp;
if (tg->bytes_disp[rw] + bio->bi_size <= bytes_allowed) {
if (wait)
*wait = 0;
return 1;
}
/* Calc approx time to dispatch */
extra_bytes = tg->bytes_disp[rw] + bio->bi_size - bytes_allowed;
jiffy_wait = div64_u64(extra_bytes * HZ, tg->bps[rw]);
if (!jiffy_wait)
jiffy_wait = 1;
/*
* This wait time is without taking into consideration the rounding
* up we did. Add that time also.
*/
jiffy_wait = jiffy_wait + (jiffy_elapsed_rnd - jiffy_elapsed);
if (wait)
*wait = jiffy_wait;
return 0;
}
/*
* Returns whether one can dispatch a bio or not. Also returns approx number
* of jiffies to wait before this bio is with-in IO rate and can be dispatched
*/
static bool tg_may_dispatch(struct throtl_data *td, struct throtl_grp *tg,
struct bio *bio, unsigned long *wait)
{
bool rw = bio_data_dir(bio);
unsigned long bps_wait = 0, iops_wait = 0, max_wait = 0;
/*
* Currently whole state machine of group depends on first bio
* queued in the group bio list. So one should not be calling
* this function with a different bio if there are other bios
* queued.
*/
BUG_ON(tg->nr_queued[rw] && bio != bio_list_peek(&tg->bio_lists[rw]));
/* If tg->bps = -1, then BW is unlimited */
if (tg->bps[rw] == -1 && tg->iops[rw] == -1) {
if (wait)
*wait = 0;
return 1;
}
/*
* If previous slice expired, start a new one otherwise renew/extend
* existing slice to make sure it is at least throtl_slice interval
* long since now.
*/
if (throtl_slice_used(td, tg, rw))
throtl_start_new_slice(td, tg, rw);
else {
if (time_before(tg->slice_end[rw], jiffies + throtl_slice))
throtl_extend_slice(td, tg, rw, jiffies + throtl_slice);
}
if (tg_with_in_bps_limit(td, tg, bio, &bps_wait)
&& tg_with_in_iops_limit(td, tg, bio, &iops_wait)) {
if (wait)
*wait = 0;
return 1;
}
max_wait = max(bps_wait, iops_wait);
if (wait)
*wait = max_wait;
if (time_before(tg->slice_end[rw], jiffies + max_wait))
throtl_extend_slice(td, tg, rw, jiffies + max_wait);
return 0;
}
static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio)
{
bool rw = bio_data_dir(bio);
bool sync = bio->bi_rw & REQ_SYNC;
/* Charge the bio to the group */
tg->bytes_disp[rw] += bio->bi_size;
tg->io_disp[rw]++;
/*
* TODO: This will take blkg->stats_lock. Figure out a way
* to avoid this cost.
*/
blkiocg_update_dispatch_stats(&tg->blkg, bio->bi_size, rw, sync);
}
static void throtl_add_bio_tg(struct throtl_data *td, struct throtl_grp *tg,
struct bio *bio)
{
bool rw = bio_data_dir(bio);
bio_list_add(&tg->bio_lists[rw], bio);
/* Take a bio reference on tg */
throtl_ref_get_tg(tg);
tg->nr_queued[rw]++;
td->nr_queued[rw]++;
throtl_enqueue_tg(td, tg);
}
static void tg_update_disptime(struct throtl_data *td, struct throtl_grp *tg)
{
unsigned long read_wait = -1, write_wait = -1, min_wait = -1, disptime;
struct bio *bio;
if ((bio = bio_list_peek(&tg->bio_lists[READ])))
tg_may_dispatch(td, tg, bio, &read_wait);
if ((bio = bio_list_peek(&tg->bio_lists[WRITE])))
tg_may_dispatch(td, tg, bio, &write_wait);
min_wait = min(read_wait, write_wait);
disptime = jiffies + min_wait;
/* Update dispatch time */
throtl_dequeue_tg(td, tg);
tg->disptime = disptime;
throtl_enqueue_tg(td, tg);
}
static void tg_dispatch_one_bio(struct throtl_data *td, struct throtl_grp *tg,
bool rw, struct bio_list *bl)
{
struct bio *bio;
bio = bio_list_pop(&tg->bio_lists[rw]);
tg->nr_queued[rw]--;
/* Drop bio reference on tg */
throtl_put_tg(tg);
BUG_ON(td->nr_queued[rw] <= 0);
td->nr_queued[rw]--;
throtl_charge_bio(tg, bio);
bio_list_add(bl, bio);
bio->bi_rw |= REQ_THROTTLED;
throtl_trim_slice(td, tg, rw);
}
static int throtl_dispatch_tg(struct throtl_data *td, struct throtl_grp *tg,
struct bio_list *bl)
{
unsigned int nr_reads = 0, nr_writes = 0;
unsigned int max_nr_reads = throtl_grp_quantum*3/4;
unsigned int max_nr_writes = throtl_grp_quantum - max_nr_reads;
struct bio *bio;
/* Try to dispatch 75% READS and 25% WRITES */
while ((bio = bio_list_peek(&tg->bio_lists[READ]))
&& tg_may_dispatch(td, tg, bio, NULL)) {
tg_dispatch_one_bio(td, tg, bio_data_dir(bio), bl);
nr_reads++;
if (nr_reads >= max_nr_reads)
break;
}
while ((bio = bio_list_peek(&tg->bio_lists[WRITE]))
&& tg_may_dispatch(td, tg, bio, NULL)) {
tg_dispatch_one_bio(td, tg, bio_data_dir(bio), bl);
nr_writes++;
if (nr_writes >= max_nr_writes)
break;
}
return nr_reads + nr_writes;
}
static int throtl_select_dispatch(struct throtl_data *td, struct bio_list *bl)
{
unsigned int nr_disp = 0;
struct throtl_grp *tg;
struct throtl_rb_root *st = &td->tg_service_tree;
while (1) {
tg = throtl_rb_first(st);
if (!tg)
break;
if (time_before(jiffies, tg->disptime))
break;
throtl_dequeue_tg(td, tg);
nr_disp += throtl_dispatch_tg(td, tg, bl);
if (tg->nr_queued[0] || tg->nr_queued[1]) {
tg_update_disptime(td, tg);
throtl_enqueue_tg(td, tg);
}
if (nr_disp >= throtl_quantum)
break;
}
return nr_disp;
}
static void throtl_process_limit_change(struct throtl_data *td)
{
struct throtl_grp *tg;
struct hlist_node *pos, *n;
if (!atomic_read(&td->limits_changed))
return;
throtl_log(td, "limit changed =%d", atomic_read(&td->limits_changed));
/*
* Make sure updates from throtl_update_blkio_group_read_bps() group
* of functions to tg->limits_changed are visible. We do not
* want update td->limits_changed to be visible but update to
* tg->limits_changed not being visible yet on this cpu. Hence
* the read barrier.
*/
smp_rmb();
hlist_for_each_entry_safe(tg, pos, n, &td->tg_list, tg_node) {
if (throtl_tg_on_rr(tg) && tg->limits_changed) {
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]);
tg_update_disptime(td, tg);
tg->limits_changed = false;
}
}
smp_mb__before_atomic_dec();
atomic_dec(&td->limits_changed);
smp_mb__after_atomic_dec();
}
/* 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;
spin_lock_irq(q->queue_lock);
throtl_process_limit_change(td);
if (!total_nr_queued(td))
goto out;
bio_list_init(&bio_list_on_stack);
throtl_log(td, "dispatch nr_queued=%lu read=%u write=%u",
total_nr_queued(td), td->nr_queued[READ],
td->nr_queued[WRITE]);
nr_disp = throtl_select_dispatch(td, &bio_list_on_stack);
if (nr_disp)
throtl_log(td, "bios disp=%u", nr_disp);
throtl_schedule_next_dispatch(td);
out:
spin_unlock_irq(q->queue_lock);
/*
* If we dispatched some requests, unplug the queue to make sure
* immediate dispatch
*/
if (nr_disp) {
while((bio = bio_list_pop(&bio_list_on_stack)))
generic_make_request(bio);
blk_unplug(q);
}
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 */
void throtl_schedule_delayed_work(struct request_queue *q, unsigned long delay)
{
struct throtl_data *td = q->td;
struct delayed_work *dwork = &td->throtl_work;
if (total_nr_queued(td) > 0) {
/*
* We might have a work scheduled to be executed in future.
* Cancel that and schedule a new one.
*/
__cancel_delayed_work(dwork);
kblockd_schedule_delayed_work(q, dwork, delay);
throtl_log(td, "schedule work. delay=%lu jiffies=%lu",
delay, jiffies);
}
}
EXPORT_SYMBOL(throtl_schedule_delayed_work);
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);
}
/*
* For all update functions, key should be a valid pointer because these
* update functions are called under blkcg_lock, that means, blkg is
* valid and in turn key is valid. queue exit path can not race becuase
* of blkcg_lock
*
* Can not take queue lock in update functions as queue lock under blkcg_lock
* is not allowed. Under other paths we take blkcg_lock under queue_lock.
*/
static void throtl_update_blkio_group_read_bps(void *key,
struct blkio_group *blkg, u64 read_bps)
{
struct throtl_data *td = key;
tg_of_blkg(blkg)->bps[READ] = read_bps;
/* Make sure read_bps is updated before setting limits_changed */
smp_wmb();
tg_of_blkg(blkg)->limits_changed = true;
/* Make sure tg->limits_changed is updated before td->limits_changed */
smp_mb__before_atomic_inc();
atomic_inc(&td->limits_changed);
smp_mb__after_atomic_inc();
/* Schedule a work now to process the limit change */
throtl_schedule_delayed_work(td->queue, 0);
}
static void throtl_update_blkio_group_write_bps(void *key,
struct blkio_group *blkg, u64 write_bps)
{
struct throtl_data *td = key;
tg_of_blkg(blkg)->bps[WRITE] = write_bps;
smp_wmb();
tg_of_blkg(blkg)->limits_changed = true;
smp_mb__before_atomic_inc();
atomic_inc(&td->limits_changed);
smp_mb__after_atomic_inc();
throtl_schedule_delayed_work(td->queue, 0);
}
static void throtl_update_blkio_group_read_iops(void *key,
struct blkio_group *blkg, unsigned int read_iops)
{
struct throtl_data *td = key;
tg_of_blkg(blkg)->iops[READ] = read_iops;
smp_wmb();
tg_of_blkg(blkg)->limits_changed = true;
smp_mb__before_atomic_inc();
atomic_inc(&td->limits_changed);
smp_mb__after_atomic_inc();
throtl_schedule_delayed_work(td->queue, 0);
}
static void throtl_update_blkio_group_write_iops(void *key,
struct blkio_group *blkg, unsigned int write_iops)
{
struct throtl_data *td = key;
tg_of_blkg(blkg)->iops[WRITE] = write_iops;
smp_wmb();
tg_of_blkg(blkg)->limits_changed = true;
smp_mb__before_atomic_inc();
atomic_inc(&td->limits_changed);
smp_mb__after_atomic_inc();
throtl_schedule_delayed_work(td->queue, 0);
}
void throtl_shutdown_timer_wq(struct request_queue *q)
{
struct throtl_data *td = q->td;
cancel_delayed_work_sync(&td->throtl_work);
}
static struct blkio_policy_type blkio_policy_throtl = {
.ops = {
.blkio_unlink_group_fn = throtl_unlink_blkio_group,
.blkio_update_group_read_bps_fn =
throtl_update_blkio_group_read_bps,
.blkio_update_group_write_bps_fn =
throtl_update_blkio_group_write_bps,
.blkio_update_group_read_iops_fn =
throtl_update_blkio_group_read_iops,
.blkio_update_group_write_iops_fn =
throtl_update_blkio_group_write_iops,
},
.plid = BLKIO_POLICY_THROTL,
};
int blk_throtl_bio(struct request_queue *q, struct bio **biop)
{
struct throtl_data *td = q->td;
struct throtl_grp *tg;
struct bio *bio = *biop;
bool rw = bio_data_dir(bio), update_disptime = true;
if (bio->bi_rw & REQ_THROTTLED) {
bio->bi_rw &= ~REQ_THROTTLED;
return 0;
}
spin_lock_irq(q->queue_lock);
tg = throtl_get_tg(td);
if (tg->nr_queued[rw]) {
/*
* There is already another bio queued in same dir. No
* need to update dispatch time.
* Still update the disptime if rate limits on this group
* were changed.
*/
if (!tg->limits_changed)
update_disptime = false;
else
tg->limits_changed = false;
goto queue_bio;
}
/* Bio is with-in rate limit of group */
if (tg_may_dispatch(td, tg, bio, NULL)) {
throtl_charge_bio(tg, bio);
goto out;
}
queue_bio:
throtl_log_tg(td, tg, "[%c] bio. bdisp=%u sz=%u bps=%llu"
" iodisp=%u iops=%u queued=%d/%d",
rw == READ ? 'R' : 'W',
tg->bytes_disp[rw], bio->bi_size, tg->bps[rw],
tg->io_disp[rw], tg->iops[rw],
tg->nr_queued[READ], tg->nr_queued[WRITE]);
throtl_add_bio_tg(q->td, tg, bio);
*biop = NULL;
if (update_disptime) {
tg_update_disptime(td, tg);
throtl_schedule_next_dispatch(td);
}
out:
spin_unlock_irq(q->queue_lock);
return 0;
}
int blk_throtl_init(struct request_queue *q)
{
struct throtl_data *td;
struct throtl_grp *tg;
td = kzalloc_node(sizeof(*td), GFP_KERNEL, q->node);
if (!td)
return -ENOMEM;
INIT_HLIST_HEAD(&td->tg_list);
td->tg_service_tree = THROTL_RB_ROOT;
atomic_set(&td->limits_changed, 0);
/* Init root group */
tg = &td->root_tg;
INIT_HLIST_NODE(&tg->tg_node);
RB_CLEAR_NODE(&tg->rb_node);
bio_list_init(&tg->bio_lists[0]);
bio_list_init(&tg->bio_lists[1]);
/* Practically unlimited BW */
tg->bps[0] = tg->bps[1] = -1;
tg->iops[0] = tg->iops[1] = -1;
/*
* Set root group reference to 2. One reference will be dropped when
* all groups on tg_list are being deleted during queue exit. Other
* reference will remain there as we don't want to delete this group
* as it is statically allocated and gets destroyed when throtl_data
* goes away.
*/
atomic_set(&tg->ref, 2);
hlist_add_head(&tg->tg_node, &td->tg_list);
td->nr_undestroyed_grps++;
INIT_DELAYED_WORK(&td->throtl_work, blk_throtl_work);
rcu_read_lock();
blkiocg_add_blkio_group(&blkio_root_cgroup, &tg->blkg, (void *)td,
0, BLKIO_POLICY_THROTL);
rcu_read_unlock();
/* Attach throtl data to request queue */
td->queue = q;
q->td = td;
return 0;
}
void blk_throtl_exit(struct request_queue *q)
{
struct throtl_data *td = q->td;
bool wait = false;
BUG_ON(!td);
throtl_shutdown_timer_wq(q);
spin_lock_irq(q->queue_lock);
throtl_release_tgs(td);
/* If there are other groups */
if (td->nr_undestroyed_grps > 0)
wait = true;
spin_unlock_irq(q->queue_lock);
/*
* Wait for tg->blkg->key accessors to exit their grace periods.
* Do this wait only if there are other undestroyed groups out
* there (other than root group). This can happen if cgroup deletion
* path claimed the responsibility of cleaning up a group before
* queue cleanup code get to the group.
*
* Do not call synchronize_rcu() unconditionally as there are drivers
* which create/delete request queue hundreds of times during scan/boot
* and synchronize_rcu() can take significant time and slow down boot.
*/
if (wait)
synchronize_rcu();
/*
* Just being safe to make sure after previous flush if some body did
* update limits through cgroup and another work got queued, cancel
* it.
*/
throtl_shutdown_timer_wq(q);
throtl_td_free(td);
}
static int __init throtl_init(void)
{
blkio_policy_register(&blkio_policy_throtl);
return 0;
}
module_init(throtl_init);
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