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authorAlan D. Brunelle <Alan.Brunelle@hp.com>2008-04-29 14:44:19 +0200
committerJens Axboe <jens.axboe@oracle.com>2008-04-29 14:48:55 +0200
commitac9fafa1243640349aa481adf473db283a695766 (patch)
tree155c2371cca8971638d781269f39fa015bc6509c /include/linux/blkdev.h
parentd7e3c3249ef23b4617393c69fe464765b4ff1645 (diff)
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 <alan.brunelle@hp.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Diffstat (limited to 'include/linux/blkdev.h')
-rw-r--r--include/linux/blkdev.h2
1 files changed, 2 insertions, 0 deletions
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)