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authorMing Lei <ming.lei@redhat.com>2018-07-02 12:35:59 +0300
committerJens Axboe <axboe@kernel.dk>2018-07-09 18:07:53 +0300
commitb04f50ab8a74129b3041a2836c33c916be3c6667 (patch)
treeccf5718c53c6afabf85f3c2597994938147f7ac9
parent3f0cedc7e9a0b32e79c79d2aac0c96d2b870ae55 (diff)
downloadlinux-b04f50ab8a74129b3041a2836c33c916be3c6667.tar.xz
blk-mq: only attempt to merge bio if there is rq in sw queue
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>
-rw-r--r--block/blk-mq-sched.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 4e027f6108ae..f3b4b5ceb4d1 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -326,7 +326,8 @@ 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);