From e240c1839d11152b0355442f8ac6d2d2d921be36 Mon Sep 17 00:00:00 2001
From: Shaohua Li <shli@kernel.org>
Date: Wed, 9 Apr 2014 11:27:42 +0800
Subject: [PATCH] raid5: get_active_stripe avoids device_lock
For sequential workload (or request size big workload), get_active_stripe can
find cached stripe. In this case, we always hold device_lock, which exposes a
lot of lock contention for such workload. If stripe count isn't 0, we don't
need hold the lock actually, since we just increase its count. And this is the
hot code path for such workload. Unfortunately we must delete the BUG_ON.
Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: NeilBrown <neilb@suse.de>
---
drivers/md/raid5.c | 9 ++-------
1 file changed, 2 insertions(+), 7 deletions(-)
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index a904a2c80fc83f..25247a8529124f 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -679,14 +679,9 @@ get_active_stripe(struct r5conf *conf, sector_t sector,
init_stripe(sh, sector, previous);
atomic_inc(&sh->count);
}
- } else {
+ } else if (!atomic_inc_not_zero(&sh->count)) {
spin_lock(&conf->device_lock);
- if (atomic_read(&sh->count)) {
- BUG_ON(!list_empty(&sh->lru)
- && !test_bit(STRIPE_EXPANDING, &sh->state)
- && !test_bit(STRIPE_ON_UNPLUG_LIST, &sh->state)
- );
- } else {
+ if (!atomic_read(&sh->count)) {
if (!test_bit(STRIPE_HANDLE, &sh->state))
atomic_inc(&conf->active_stripes);
BUG_ON(list_empty(&sh->lru) &&
--
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