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Commit 0e5313e2 authored by Tomasz Majchrzak's avatar Tomasz Majchrzak Committed by Shaohua Li
Browse files

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: default avatarTomasz Majchrzak <tomasz.majchrzak@intel.com>
Signed-off-by: default avatarShaohua Li <shli@fb.com>
parent 573275b5

drivers/md/raid10.c

+12 −9
Original line number Diff line number Diff line
@@ -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)

drivers/md/raid10.h

+2 −1
Original line number Diff line number Diff line
@@ -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).