commit 01e99aeca397 causes longer runtime of block/004

Shinichiro Kawasaki
2020-03-04T02:39:54Z

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?

--
Best Regards,
Shin'ichiro Kawasaki