[PATCH] blk: no memory barrier

This memory barrier is not needed because the waitqueue will only get waiters
on it in the following situations:

rq->count has exceeded the threshold - however all manipulations of ->count
are performed under the runqueue lock, and so we will correctly pick up any
waiter.

Memory allocation for the request fails.  In this case, there is no additional
help provided by the memory barrier.  We are guaranteed to eventually wake up
waiters because the request allocation mempool guarantees that if the mem
allocation for a request fails, there must be some requests in flight.  They
will wake up waiters when they are retired.

Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Jens Axboe <axboe@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/drivers/block/ll_rw_blk.c b/drivers/block/ll_rw_blk.c
index c581f9138c472277f898506b3c7c58606693d9c8..265de858d4dea9e5121a74f14edbbbb418d17cd6 100644 (file)
--- a/drivers/block/ll_rw_blk.c
+++ b/drivers/block/ll_rw_blk.c
@@ -1842,7 +1842,6 @@ static void __freed_request(request_queue_t *q, int rw)
                clear_queue_congested(q, rw);
 
        if (rl->count[rw] + 1 <= q->nr_requests) {
-               smp_mb();
                if (waitqueue_active(&rl->wait[rw]))
                        wake_up(&rl->wait[rw]);