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@xxxxxxxxx>
---
drivers/md/raid10.c | 21 ++++++++++++---------
drivers/md/raid10.h | 3 ++-
2 files changed, 14 insertions(+), 10 deletions(-)
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index e3fd725..cdbe504 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -913,7 +913,7 @@ 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);
@@ -944,23 +944,23 @@ 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);
- wake_up(&conf->wait_barrier);
+ if ((atomic_dec_and_test(&conf->nr_pending)) ||
+ (conf->array_freeze_pending))
+ wake_up(&conf->wait_barrier);
}
static void freeze_array(struct r10conf *conf, int extra)
@@ -978,13 +978,15 @@ 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);
}
@@ -3505,6 +3507,7 @@ 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)
diff --git a/drivers/md/raid10.h b/drivers/md/raid10.h
index 6fc2c75..18ec1f7 100644
--- a/drivers/md/raid10.h
+++ b/drivers/md/raid10.h
@@ -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).
--
1.8.3.1
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
