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>
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 @@
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).