diff options
| author | Ming Lei <ming.lei@redhat.com> | 2018-07-02 12:35:59 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-09-26 09:39:43 +0300 |
| commit | 864e90ed4a8f4a37b20effa5c06b7b5902ebcab9 (patch) | |
| tree | 4f6a158e6cc219380f718e4b37e50a2d4f47ed66 | |
| parent | 83459da8e319f5625ad4a089c926b5dc5bafb6fe (diff) | |
| download | linux-864e90ed4a8f4a37b20effa5c06b7b5902ebcab9.tar.xz | |
blk-mq: only attempt to merge bio if there is rq in sw queue
[ Upstream commit b04f50ab8a74129b3041a2836c33c916be3c6667 ]
Only attempt to merge bio iff the ctx->rq_list isn't empty, because:
1) for high-performance SSD, most of times dispatch may succeed, then
there may be nothing left in ctx->rq_list, so don't try to merge over
sw queue if it is empty, then we can save one acquiring of ctx->lock
2) we can't expect good merge performance on per-cpu sw queue, and missing
one merge on sw queue won't be a big deal since tasks can be scheduled from
one CPU to another.
Cc: Laurence Oberman <loberman@redhat.com>
Cc: Omar Sandoval <osandov@fb.com>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Tested-by: Kashyap Desai <kashyap.desai@broadcom.com>
Reported-by: Kashyap Desai <kashyap.desai@broadcom.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | block/blk-mq-sched.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c index 56c493c6cd90..f5745acc2d98 100644 --- a/block/blk-mq-sched.c +++ b/block/blk-mq-sched.c @@ -339,7 +339,8 @@ bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio) return e->type->ops.mq.bio_merge(hctx, bio); } - if (hctx->flags & BLK_MQ_F_SHOULD_MERGE) { + if ((hctx->flags & BLK_MQ_F_SHOULD_MERGE) && + !list_empty_careful(&ctx->rq_list)) { /* default per sw-queue merge */ spin_lock(&ctx->lock); ret = blk_mq_attempt_merge(q, ctx, bio); |