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Date:   Tue, 16 Aug 2022 18:25:23 +0300
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Subject: Re: stalling IO regression since linux 5.12, through 5.18
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To:     Chris Murphy <lists@colorremedies.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>
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From:   Nikolay Borisov <nborisov@suse.com>
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On 16.08.22 г. 17:22 ч., Chris Murphy wrote:
> 
> 
> 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 bfq
>> 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 calculations
>> 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 merging
>> 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 intensity
>>>>> 1a23e06cdab2 bfq: don't duplicate code for different paths
>> 2391d13ed484 block, bfq: do not expire a queue when it is the only busy
>> 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 log
>> 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/view?usp=sharing
> 
> Any suggestions for further testing? I could try go down farther in the bisect.txt list. The problem is if the hardware falls over on an unbootable kernel, I have to bug someone with LOM access. That's a limited resource.
> 
> 

How about changing the scheduler either mq-deadline or noop, just to see 
if this is also reproducible with a different scheduler. I guess noop 
would imply the blk cgroup controller is going to be disabled