linux-kernel - Re: stalling IO regression since linux 5.12, through 5.18

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Message-Id: <f633c476-bdc9-40e2-a93f-29601979f833@www.fastmail.com>
Date:   Wed, 17 Aug 2022 11:02:25 -0400
From:   "Chris Murphy" <lists@...orremedies.com>
To:     "Ming Lei" <ming.lei@...hat.com>
Cc:     "Nikolay Borisov" <nborisov@...e.com>,
        "Jens Axboe" <axboe@...nel.dk>, "Jan Kara" <jack@...e.cz>,
        "Paolo Valente" <paolo.valente@...aro.org>,
        "Btrfs BTRFS" <linux-btrfs@...r.kernel.org>,
        Linux-RAID <linux-raid@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Josef Bacik" <josef@...icpanda.com>
Subject: Re: stalling IO regression since linux 5.12, through 5.18



On Wed, Aug 17, 2022, at 10:53 AM, Ming Lei wrote:
> On Wed, Aug 17, 2022 at 10:34:38AM -0400, Chris Murphy wrote:
>> 
>> 
>> On Wed, Aug 17, 2022, at 8:06 AM, Ming Lei wrote:
>> 
>> > blk-mq debugfs log is usually helpful for io stall issue, care to post
>> > the blk-mq debugfs log:
>> >
>> > (cd /sys/kernel/debug/block/$disk && find . -type f -exec grep -aH . {} \;)
>> 
>> This is only sda
>> https://drive.google.com/file/d/1aAld-kXb3RUiv_ShAvD_AGAFDRS03Lr0/view?usp=sharing
>
> From the log, there isn't any in-flight IO request.
>
> So please confirm that it is collected after the IO stall is triggered.

Yes, iotop reports no reads or writes at the time of collection. IO pressure 99% for auditd, systemd-journald, rsyslogd, and postgresql, with increasing pressure from all the qemu processes.

Keep in mind this is a raid10, so maybe it's enough for just one block device IO to stall and the whole thing stops? That's why I included all block devices.

> If yes, the issue may not be related with BFQ, and should be related
> with blk-cgroup code.

Problem happens with cgroup.disable=io, does this setting affect blk-cgroup?

-- 
Chris Murphy