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

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Message-ID: <BYAPR21MB127006555030F7BFA47FDAABBF749@BYAPR21MB1270.namprd21.prod.outlook.com>
Date:   Mon, 13 Dec 2021 04:20:49 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     Ming Lei <ming.lei@...hat.com>
CC:     Jens Axboe <axboe@...nel.dk>, 'Christoph Hellwig' <hch@....de>,
        "'linux-block@...r.kernel.org'" <linux-block@...r.kernel.org>,
        Long Li <longli@...rosoft.com>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        "'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>
Subject: RE: Random high CPU utilization in blk-mq with the none scheduler

> From: Ming Lei <ming.lei@...hat.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.

Download attachment "dm-sd.log.zip" of type "application/x-zip-compressed" (608996 bytes)