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raid10: improve random reads performance 

RAID10 random read performance is lower than expected due to excessive spinlock
utilisation which is required mostly for rebuild/resync. Simplify allow_barrier
as it's in IO path and encounters a lot of unnecessary congestion.

As lower_barrier just takes a lock in order to decrement a counter, convert
counter (nr_pending) into atomic variable and remove the spin lock. There is
also a congestion for wake_up (it uses lock internally) so call it only when
it's really needed. As wake_up is not called constantly anymore, ensure process
waiting to raise a barrier is notified when there are no more waiting IOs.

Signed-off-by: Tomasz Majchrzak <tomasz.majchrzak@intel.com>
Signed-off-by: Shaohua Li <shli@fb.com>
This commit is contained in:
Tomasz Majchrzak 2016-06-24 14:20:16 +02:00 committed by Shaohua Li
parent 573275b58e
commit 0e5313e2d4
2 changed files with 14 additions and 10 deletions
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19
drivers/md/raid10.c
View File

@ -905,7 +905,7 @@ static void raise_barrier(struct r10conf *conf, int force)
/* Now wait for all pending IO to complete */
wait_event_lock_irq(conf->wait_barrier,
!conf->nr_pending && conf->barrier < RESYNC_DEPTH,
!atomic_read(&conf->nr_pending) && conf->barrier < RESYNC_DEPTH,
conf->resync_lock);
spin_unlock_irq(&conf->resync_lock);
@ -936,22 +936,22 @@ static void wait_barrier(struct r10conf *conf)
*/
wait_event_lock_irq(conf->wait_barrier,
!conf->barrier ||
(conf->nr_pending &&
(atomic_read(&conf->nr_pending) &&
current->bio_list &&
!bio_list_empty(current->bio_list)),
conf->resync_lock);
conf->nr_waiting--;
if (!conf->nr_waiting)
wake_up(&conf->wait_barrier);
}
conf->nr_pending++;
atomic_inc(&conf->nr_pending);
spin_unlock_irq(&conf->resync_lock);
}
static void allow_barrier(struct r10conf *conf)
{
unsigned long flags;
spin_lock_irqsave(&conf->resync_lock, flags);
conf->nr_pending--;
spin_unlock_irqrestore(&conf->resync_lock, flags);
if ((atomic_dec_and_test(&conf->nr_pending)) ||
(conf->array_freeze_pending))
wake_up(&conf->wait_barrier);
}
@ -970,13 +970,15 @@ static void freeze_array(struct r10conf *conf, int extra)
* we continue.
*/
spin_lock_irq(&conf->resync_lock);
conf->array_freeze_pending++;
conf->barrier++;
conf->nr_waiting++;
wait_event_lock_irq_cmd(conf->wait_barrier,
conf->nr_pending == conf->nr_queued+extra,
atomic_read(&conf->nr_pending) == conf->nr_queued+extra,
conf->resync_lock,
flush_pending_writes(conf));
conf->array_freeze_pending--;
spin_unlock_irq(&conf->resync_lock);
}
@ -3542,6 +3544,7 @@ static struct r10conf *setup_conf(struct mddev *mddev)
spin_lock_init(&conf->resync_lock);
init_waitqueue_head(&conf->wait_barrier);
atomic_set(&conf->nr_pending, 0);
conf->thread = md_register_thread(raid10d, mddev, "raid10");
if (!conf->thread)

3
drivers/md/raid10.h
View File

@ -64,10 +64,11 @@ struct r10conf {
int pending_count;
spinlock_t resync_lock;
int nr_pending;
atomic_t nr_pending;
int nr_waiting;
int nr_queued;
int barrier;
int array_freeze_pending;
sector_t next_resync;
int fullsync; /* set to 1 if a full sync is needed,
* (fresh device added).