From ac9fafa1243640349aa481adf473db283a695766 Mon Sep 17 00:00:00 2001 From: "Alan D. Brunelle" Date: Tue, 29 Apr 2008 14:44:19 +0200 Subject: block: Skip I/O merges when disabled The block I/O + elevator + I/O scheduler code spend a lot of time trying to merge I/Os -- rightfully so under "normal" circumstances. However, if one were to know that the incoming I/O stream was /very/ random in nature, the cycles are wasted. This patch adds a per-request_queue tunable that (when set) disables merge attempts (beyond the simple one-hit cache check), thus freeing up a non-trivial amount of CPU cycles. Signed-off-by: Alan D. Brunelle Signed-off-by: Jens Axboe --- block/elevator.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'block/elevator.c') diff --git a/block/elevator.c b/block/elevator.c index 7253fa05db0..ac5310ef827 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -488,6 +488,9 @@ int elv_merge(struct request_queue *q, struct request **req, struct bio *bio) } } + if (blk_queue_nomerges(q)) + return ELEVATOR_NO_MERGE; + /* * See if our hash lookup can find a potential backmerge. */ -- cgit v1.2.3