On Mar 04, 2020 / 17:53, Ming Lei wrote: > On Wed, Mar 04, 2020 at 06:11:37AM +0000, Shinichiro Kawasaki wrote: > > On Mar 04, 2020 / 11:46, Ming Lei wrote: > > > On Wed, Mar 04, 2020 at 02:38:43AM +0000, Shinichiro Kawasaki wrote: > > > > I noticed that blktests block/004 takes longer runtime with 5.6-rc4 than > > > > 5.6-rc3, and found that the commit 01e99aeca397 ("blk-mq: insert passthrough > > > > request into hctx->dispatch directly") triggers it. > > > > > > > > The longer runtime was observed with dm-linear device which maps SATA SMR HDD > > > > connected via AHCI. It was not observed with dm-linear on SAS/SATA SMR HDDs > > > > connected via SAS-HBA. Not observed with dm-linear on non-SMR HDDs either. > > > > > > > > Before the commit, block/004 took around 130 seconds. After the commit, it takes > > > > around 300 seconds. I need to dig in further details to understand why the > > > > commit makes the test case longer. > > > > > > > > The test case block/004 does "flush intensive workload". Is this longer runtime > > > > expected? > > > > > > The following patch might address this issue: > > > > > > https://lore.kernel.org/linux-block/20200207190416.99928-1-sqazi@xxxxxxxxxx/#t > > > > > > Please test and provide us the result. > > > > > > thanks, > > > Ming > > > > > > > Hi Ming, > > > > I applied the patch to 5.6-rc4 but I observed the longer runtime of block/004. > > Still it takes around 300 seconds. > > Hello Shinichiro, > > block/004 only sends 1564 sync randwrite, and seems 130s has been slow > enough. > > There are two related effect in that commit for your issue: > > 1) 'at_head' is applied in blk_mq_sched_insert_request() for flush > request > > 2) all IO is added back to tail of hctx->dispatch after .queue_rq() > returns STS_RESOURCE > > Seems it is more related with 2) given you can't reproduce the issue on > SAS. > > So please test the following two patches, and see which one makes a > difference for you. > > BTW, both two looks not reasonable, just for narrowing down the issue. > > 1) patch 1 > > diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c > index 856356b1619e..86137c75283c 100644 > --- a/block/blk-mq-sched.c > +++ b/block/blk-mq-sched.c > @@ -398,7 +398,7 @@ void blk_mq_sched_insert_request(struct request *rq, bool at_head, > WARN_ON(e && (rq->tag != -1)); > > if (blk_mq_sched_bypass_insert(hctx, !!e, rq)) { > - blk_mq_request_bypass_insert(rq, at_head, false); > + blk_mq_request_bypass_insert(rq, true, false); > goto run; > } Ming, thank you for the trial patches. This "patch 1" reduced the runtime, as short as rc3. > > > 2) patch 2 > diff --git a/block/blk-mq.c b/block/blk-mq.c > index d92088dec6c3..447d5cb39832 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -1286,7 +1286,7 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list, > q->mq_ops->commit_rqs(hctx); > > spin_lock(&hctx->lock); > - list_splice_tail_init(list, &hctx->dispatch); > + list_splice_init(list, &hctx->dispatch); > spin_unlock(&hctx->lock); > > /* This patch 2 didn't reduce the runtime. Wish this report helps. -- Best Regards, Shin'ichiro Kawasaki