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blk-mq: Micro-optimize blk_queue_nomerges() check 

In blk_mq_make_request(), do the blk_queue_nomerges() check
outside the call to blk_attempt_plug_merge() to eliminate
function call overhead when nomerges=2 (disabled)

Signed-off-by: Robert Elliott <elliott@hp.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Robert Elliott 2014-05-20 16:46:26 -05:00 committed by Jens Axboe
parent eba7176826
commit da41a589f5
2 changed files with 6 additions and 5 deletions
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8
block/blk-core.c
View File

@ -1471,6 +1471,8 @@ bool bio_attempt_front_merge(struct request_queue *q, struct request *req,
* added on the elevator at this point. In addition, we don't have * added on the elevator at this point. In addition, we don't have
* reliable access to the elevator outside queue lock. Only check basic * reliable access to the elevator outside queue lock. Only check basic
* merging parameters without querying the elevator. * merging parameters without querying the elevator.
*
* Caller must ensure !blk_queue_nomerges(q) beforehand.
*/ */
bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio, bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
unsigned int *request_count) unsigned int *request_count)
@ -1480,9 +1482,6 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
bool ret = false; bool ret = false;
struct list_head *plug_list; struct list_head *plug_list;
if (blk_queue_nomerges(q))
goto out;
plug = current->plug; plug = current->plug;
if (!plug) if (!plug)
goto out; goto out;
@ -1561,7 +1560,8 @@ void blk_queue_bio(struct request_queue *q, struct bio *bio)
* Check if we can merge with the plugged list before grabbing * Check if we can merge with the plugged list before grabbing
* any locks. * any locks.
*/ */
if (blk_attempt_plug_merge(q, bio, &request_count)) if (!blk_queue_nomerges(q) &&
blk_attempt_plug_merge(q, bio, &request_count))
return; return;
spin_lock_irq(q->queue_lock); spin_lock_irq(q->queue_lock);

3
block/blk-mq.c
View File

@ -1087,7 +1087,8 @@ static void blk_mq_make_request(struct request_queue *q, struct bio *bio)
return; return;
} }
if (use_plug && blk_attempt_plug_merge(q, bio, &request_count)) if (use_plug && !blk_queue_nomerges(q) &&
blk_attempt_plug_merge(q, bio, &request_count))
return; return;
if (blk_mq_queue_enter(q)) { if (blk_mq_queue_enter(q)) {