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 --- include/linux/blkdev.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include/linux/blkdev.h') diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 08df1ea8bac4..c09696a90d6a 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -408,6 +408,7 @@ struct request_queue #define QUEUE_FLAG_PLUGGED 7 /* queue is plugged */ #define QUEUE_FLAG_ELVSWITCH 8 /* don't use elevator, just do FIFO */ #define QUEUE_FLAG_BIDI 9 /* queue supports bidi requests */ +#define QUEUE_FLAG_NOMERGES 10 /* disable merge attempts */ static inline void queue_flag_set_unlocked(unsigned int flag, struct request_queue *q) @@ -476,6 +477,7 @@ enum { #define blk_queue_plugged(q) test_bit(QUEUE_FLAG_PLUGGED, &(q)->queue_flags) #define blk_queue_tagged(q) test_bit(QUEUE_FLAG_QUEUED, &(q)->queue_flags) #define blk_queue_stopped(q) test_bit(QUEUE_FLAG_STOPPED, &(q)->queue_flags) +#define blk_queue_nomerges(q) test_bit(QUEUE_FLAG_NOMERGES, &(q)->queue_flags) #define blk_queue_flushing(q) ((q)->ordseq) #define blk_fs_request(rq) ((rq)->cmd_type == REQ_TYPE_FS) -- cgit v1.2.3-71-gd317