RE: Random high CPU utilization in blk-mq with the none scheduler

Dexuan Cui
2021-12-13T04:21:06Z

[-- Attachment #1: Type: text/plain, Size: 933 bytes --]

> From: Ming Lei <ming.lei@redhat.com>
> ...
> Can you provide the following blk-mq debugfs log?
>
> (cd /sys/kernel/debug/block/dm-N && find . -type f -exec grep -aH . {} \;)
>
> (cd /sys/kernel/debug/block/sdN && find . -type f -exec grep -aH . {} \;)
>
> And it is enough to just collect log from one dm-mpath & one underlying iscsi
> disk,
> so we can understand basic blk-mq setting, such as nr_hw_queues, queue
> depths, ...
>
> Thanks,
> Ming

Attached. I collected the logs for all the dm-* and sd* devices against
v5.16-rc4 with the 3 commits reverted:
b22809092c70 ("block: replace always false argument with 'false'")
ff1552232b36 ("blk-mq: don't issue request directly in case that current is to be blocked")
dc5fc361d891 ("block: attempt direct issue of plug list")

v5.16-rc4 does not reproduce the issue, so I'm pretty sure b22809092c70 is the
patch that resolves the excessive CPU usage.

[-- Attachment #2: dm-sd.log.zip --]
[-- Type: application/x-zip-compressed, Size: 608996 bytes --]