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blkio: Recalculate the throttled bio dispatch time upon throttle limit change 

o Currently any cgroup throttle limit changes are processed asynchronousy and
  the change does not take affect till a new bio is dispatched from same group.

o It might happen that a user sets a redicuously low limit on throttling.
  Say 1 bytes per second on reads. In such cases simple operations like mount
  a disk can wait for a very long time.

o Once bio is throttled, there is no easy way to come out of that wait even if
  user increases the read limit later.

o This patch fixes it. Now if a user changes the cgroup limits, we recalculate
  the bio dispatch time according to new limits.

o Can't take queueu lock under blkcg_lock, hence after the change I wake
  up the dispatch thread again which recalculates the time. So there are some
  variables being synchronized across two threads without lock and I had to
  make use of barriers. Hoping I have used barriers correctly. Any review of
  memory barrier code especially will help.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
This commit is contained in:
Vivek Goyal 2010-10-01 14:49:49 +02:00 committed by Jens Axboe
parent 02977e4af7
commit fe0714377e
4 changed files with 139 additions and 35 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
block/blk-cgroup.c
View File

@ -124,7 +124,8 @@ blkio_update_group_weight(struct blkio_group *blkg, unsigned int weight)
if (blkiop->plid != blkg->plid)
continue;
if (blkiop->ops.blkio_update_group_weight_fn)
blkiop->ops.blkio_update_group_weight_fn(blkg, weight);
blkiop->ops.blkio_update_group_weight_fn(blkg->key,
blkg, weight);
}
}
@ -141,11 +142,13 @@ static inline void blkio_update_group_bps(struct blkio_group *blkg, u64 bps,
if (fileid == BLKIO_THROTL_read_bps_device
&& blkiop->ops.blkio_update_group_read_bps_fn)
blkiop->ops.blkio_update_group_read_bps_fn(blkg, bps);
blkiop->ops.blkio_update_group_read_bps_fn(blkg->key,
blkg, bps);
if (fileid == BLKIO_THROTL_write_bps_device
&& blkiop->ops.blkio_update_group_write_bps_fn)
blkiop->ops.blkio_update_group_write_bps_fn(blkg, bps);
blkiop->ops.blkio_update_group_write_bps_fn(blkg->key,
blkg, bps);
}
}
@ -162,11 +165,13 @@ static inline void blkio_update_group_iops(struct blkio_group *blkg,
if (fileid == BLKIO_THROTL_read_iops_device
&& blkiop->ops.blkio_update_group_read_iops_fn)
blkiop->ops.blkio_update_group_read_iops_fn(blkg, iops);
blkiop->ops.blkio_update_group_read_iops_fn(blkg->key,
blkg, iops);
if (fileid == BLKIO_THROTL_write_iops_device
&& blkiop->ops.blkio_update_group_write_iops_fn)
blkiop->ops.blkio_update_group_write_iops_fn(blkg,iops);
blkiop->ops.blkio_update_group_write_iops_fn(blkg->key,
blkg,iops);
}
}

21
block/blk-cgroup.h
View File

@ -186,16 +186,17 @@ extern unsigned int blkcg_get_write_iops(struct blkio_cgroup *blkcg,
dev_t dev);
typedef void (blkio_unlink_group_fn) (void *key, struct blkio_group *blkg);
typedef void (blkio_update_group_weight_fn) (struct blkio_group *blkg,
unsigned int weight);
typedef void (blkio_update_group_read_bps_fn) (struct blkio_group *blkg,
u64 read_bps);
typedef void (blkio_update_group_write_bps_fn) (struct blkio_group *blkg,
u64 write_bps);
typedef void (blkio_update_group_read_iops_fn) (struct blkio_group *blkg,
unsigned int read_iops);
typedef void (blkio_update_group_write_iops_fn) (struct blkio_group *blkg,
unsigned int write_iops);
typedef void (blkio_update_group_weight_fn) (void *key,
struct blkio_group *blkg, unsigned int weight);
typedef void (blkio_update_group_read_bps_fn) (void * key,
struct blkio_group *blkg, u64 read_bps);
typedef void (blkio_update_group_write_bps_fn) (void *key,
struct blkio_group *blkg, u64 write_bps);
typedef void (blkio_update_group_read_iops_fn) (void *key,
struct blkio_group *blkg, unsigned int read_iops);
typedef void (blkio_update_group_write_iops_fn) (void *key,
struct blkio_group *blkg, unsigned int write_iops);
struct blkio_policy_ops {
blkio_unlink_group_fn *blkio_unlink_group_fn;

134
block/blk-throttle.c
View File

@ -70,6 +70,9 @@ struct throtl_grp {
/* 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
@ -93,6 +96,8 @@ struct throtl_data
/* Work for dispatching throttled bios */
struct delayed_work throtl_work;
atomic_t limits_changed;
};
enum tg_state_flags {
@ -592,15 +597,6 @@ static void tg_update_disptime(struct throtl_data *td, struct throtl_grp *tg)
min_wait = min(read_wait, write_wait);
disptime = jiffies + min_wait;
/*
* If group is already on active tree, then update dispatch time
* only if it is lesser than existing dispatch time. Otherwise
* always update the dispatch time
*/
if (throtl_tg_on_rr(tg) && time_before(disptime, tg->disptime))
return;
/* Update dispatch time */
throtl_dequeue_tg(td, tg);
tg->disptime = disptime;
@ -691,6 +687,46 @@ static int throtl_select_dispatch(struct throtl_data *td, struct bio_list *bl)
return nr_disp;
}
static void throtl_process_limit_change(struct throtl_data *td)
{
struct throtl_grp *tg;
struct hlist_node *pos, *n;
/*
* Make sure atomic_inc() effects from
* throtl_update_blkio_group_read_bps(), group of functions are
* visible.
* Is this required or smp_mb__after_atomic_inc() was suffcient
* after the atomic_inc().
*/
smp_rmb();
if (!atomic_read(&td->limits_changed))
return;
throtl_log(td, "limit changed =%d", atomic_read(&td->limits_changed));
hlist_for_each_entry_safe(tg, pos, n, &td->tg_list, tg_node) {
/*
* Do I need an smp_rmb() here to make sure tg->limits_changed
* update is visible. I am relying on smp_rmb() at the
* beginning of function and not putting a new one here.
*/
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)
{
@ -701,6 +737,8 @@ static int throtl_dispatch(struct request_queue *q)
spin_lock_irq(q->queue_lock);
throtl_process_limit_change(td);
if (!total_nr_queued(td))
goto out;
@ -821,28 +859,74 @@ void throtl_unlink_blkio_group(void *key, struct blkio_group *blkg)
spin_unlock_irqrestore(td->queue->queue_lock, flags);
}
static void throtl_update_blkio_group_read_bps (struct blkio_group *blkg,
u64 read_bps)
/*
* 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 (struct blkio_group *blkg,
u64 write_bps)
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 (struct blkio_group *blkg,
unsigned int read_iops)
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 (struct blkio_group *blkg,
unsigned int write_iops)
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)
@ -886,8 +970,14 @@ int blk_throtl_bio(struct request_queue *q, struct bio **biop)
/*
* 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.
*/
update_disptime = false;
if (!tg->limits_changed)
update_disptime = false;
else
tg->limits_changed = false;
goto queue_bio;
}
@ -929,6 +1019,7 @@ int blk_throtl_init(struct request_queue *q)
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;
@ -996,6 +1087,13 @@ void blk_throtl_exit(struct request_queue *q)
*/
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);
}

4
block/cfq-iosched.c
View File

@ -951,8 +951,8 @@ static inline struct cfq_group *cfqg_of_blkg(struct blkio_group *blkg)
return NULL;
}
void
cfq_update_blkio_group_weight(struct blkio_group *blkg, unsigned int weight)
void cfq_update_blkio_group_weight(void *key, struct blkio_group *blkg,
unsigned int weight)
{
cfqg_of_blkg(blkg)->weight = weight;
}