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>
diff --git a/block/blk-core.c b/block/blk-core.c
index fe81e19..5b6f768 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1471,6 +1471,8 @@
* added on the elevator at this point. In addition, we don't have
* reliable access to the elevator outside queue lock. Only check basic
* 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,
unsigned int *request_count)
@@ -1480,9 +1482,6 @@
bool ret = false;
struct list_head *plug_list;
- if (blk_queue_nomerges(q))
- goto out;
-
plug = current->plug;
if (!plug)
goto out;
@@ -1561,7 +1560,8 @@
* Check if we can merge with the plugged list before grabbing
* 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;
spin_lock_irq(q->queue_lock);