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Date:   Tue, 16 Aug 2022 11:34:00 -0400
From:   "Chris Murphy" <lists@colorremedies.com>
To:     "Nikolay Borisov" <nborisov@suse.com>,
        "Jens Axboe" <axboe@kernel.dk>, "Jan Kara" <jack@suse.cz>,
        "Paolo Valente" <paolo.valente@linaro.org>
Cc:     "Btrfs BTRFS" <linux-btrfs@vger.kernel.org>,
        Linux-RAID <linux-raid@vger.kernel.org>,
        linux-block <linux-block@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        "Josef Bacik" <josef@toxicpanda.com>
Subject: Re: stalling IO regression since linux 5.12, through 5.18
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On Tue, Aug 16, 2022, at 11:25 AM, Nikolay Borisov wrote:
> On 16.08.22 =D0=B3. 17:22 =D1=87., Chris Murphy wrote:
>>=20
>>=20
>> On Sun, Aug 14, 2022, at 4:28 PM, Chris Murphy wrote:
>>> On Fri, Aug 12, 2022, at 2:02 PM, Jens Axboe wrote:
>>>> Might be worth trying to revert those from 5.12 to see if they are
>>>> causing the issue? Jan, Paolo - does this ring any bells?
>>>
>>> git log --oneline --no-merges v5.11..c03c21ba6f4e > bisect.txt
>>>
>>> I tried checking out a33df75c6328, which is right before the first b=
fq
>>> commit, but that kernel won't boot the hardware.
>>>
>>> Next I checked out v5.12, then reverted these commits in order (that
>>> they were found in the bisect.txt file):
>>>
>>> 7684fbde4516 bfq: Use only idle IO periods for think time calculatio=
ns
>>> 28c6def00919 bfq: Use 'ttime' local variable
>>> 41e76c85660c bfq: Avoid false bfq queue merging
>>>>>> a5bf0a92e1b8 bfq: bfq_check_waker() should be static
>>> 71217df39dc6 block, bfq: make waker-queue detection more robust
>>> 5a5436b98d5c block, bfq: save also injection state on queue merging
>>> e673914d52f9 block, bfq: save also weight-raised service on queue me=
rging
>>> d1f600fa4732 block, bfq: fix switch back from soft-rt weitgh-raising
>>> 7f1995c27b19 block, bfq: re-evaluate convenience of I/O plugging on =
rq arrivals
>>> eb2fd80f9d2c block, bfq: replace mechanism for evaluating I/O intens=
ity
>>>>>> 1a23e06cdab2 bfq: don't duplicate code for different paths
>>> 2391d13ed484 block, bfq: do not expire a queue when it is the only b=
usy
>>> one
>>> 3c337690d2eb block, bfq: avoid spurious switches to soft_rt of
>>> interactive queues
>>> 91b896f65d32 block, bfq: do not raise non-default weights
>>> ab1fb47e33dc block, bfq: increase time window for waker detection
>>> d4fc3640ff36 block, bfq: set next_rq to waker_bfqq->next_rq in waker
>>> injection
>>> b5f74ecacc31 block, bfq: use half slice_idle as a threshold to check
>>> short ttime
>>>
>>> The two commits prefixed by >>> above were not previously mentioned =
by
>>> Jens, but I reverted them anyway because they showed up in the git l=
og
>>> command.
>>>
>>> OK so, within 10 minutes the problem does happen still. This is
>>> block/bfq-iosched.c resulting from the above reverts, in case anyone
>>> wants to double check what I did:
>>> https://drive.google.com/file/d/1ykU7MpmylJuXVobODWiiaLJk-XOiAjSt/vi=
ew?usp=3Dsharing
>>=20
>> Any suggestions for further testing? I could try go down farther in t=
he bisect.txt list. The problem is if the hardware falls over on an unbo=
otable kernel, I have to bug someone with LOM access. That's a limited r=
esource.
>>=20
>>=20
>
> How about changing the scheduler either mq-deadline or noop, just to s=
ee=20
> if this is also reproducible with a different scheduler. I guess noop=20
> would imply the blk cgroup controller is going to be disabled

I already reported on that: always happens with bfq within an hour or le=
ss. Doesn't happen with mq-deadline for ~25+ hours. Does happen with bfq=
 with the above patches removed. Does happen with cgroup.disabled=3Dio s=
et.

Sounds to me like it's something bfq depends on and is somehow becoming =
perturbed in a way that mq-deadline does not, and has changed between 5.=
11 and 5.12. I have no idea what's under bfq that matches this descripti=
on.

--=20
Chris Murphy