diff options
authorShaohua Li <>2012-04-06 11:37:47 -0600
committerJens Axboe <>2012-04-06 11:37:47 -0600
commit1b2e19f17ed327af6add02978efdf354e4f8e4df (patch)
parent407ac95e2271a310016ced97f407676e79c53c06 (diff)
block: make auto block plug flush threshold per-disk basedfor-3.4/corefor-3.4/core
We do auto block plug flush to reduce latency, the threshold is 16 requests. This works well if the task is accessing one or two drives. The problem is if the task is accessing a raid 0 device and the raid disk number is big, say 8 or 16, 16/8 = 2 or 16/16=1, we will have heavy lock contention. This patch makes the threshold per-disk based. The latency should be still ok accessing one or two drives. The setup with application accessing a lot of drives in the meantime uaually is big machine, avoiding lock contention is more important, because any contention will actually increase latency. Signed-off-by: Shaohua Li <> Signed-off-by: Jens Axboe <>
1 files changed, 2 insertions, 1 deletions
diff --git a/block/blk-core.c b/block/blk-core.c
index 414e8224588f..1f61b74867e4 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1277,7 +1277,8 @@ static bool attempt_plug_merge(struct request_queue *q, struct bio *bio,
list_for_each_entry_reverse(rq, &plug->list, queuelist) {
int el_ret;
- (*request_count)++;
+ if (rq->q == q)
+ (*request_count)++;
if (rq->q != q || !blk_rq_merge_ok(rq, bio))