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

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Date:   Tue, 16 Aug 2022 10:22:41 -0400
From:   "Chris Murphy" <lists@...orremedies.com>
To:     "Jens Axboe" <axboe@...nel.dk>, "Jan Kara" <jack@...e.cz>,
        "Paolo Valente" <paolo.valente@...aro.org>
Cc:     "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 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.


-- 
Chris Murphy