linux-kernel - Re: [Intel-gfx] WQ_UNBOUND warning since recent workqueue refactoring

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Message-ID: <2e31f088-72e5-6a15-4210-2a721c422d1d@gmail.com>
Date:   Wed, 30 Aug 2023 21:54:17 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     imre.deak@...el.com, Tejun Heo <tj@...nel.org>
Cc:     intel-gfx@...ts.freedesktop.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>
Subject: Re: [Intel-gfx] WQ_UNBOUND warning since recent workqueue refactoring

On 30.08.2023 20:56, Imre Deak wrote:
> On Wed, Aug 30, 2023 at 07:51:13AM -1000, Tejun Heo wrote:
> Hi,
> 
>> Hello,
>>
>> (cc'ing i915 folks)
>>
>> On Wed, Aug 30, 2023 at 04:57:42PM +0200, Heiner Kallweit wrote:
>>> Recently I started to see the following warning on linux-next and presumably
>>> this may be related to the refactoring of the workqueue core code.
>>>
>>> [   56.900223] workqueue: output_poll_execute [drm_kms_helper] hogged CPU for >10000us 4 times, consider switching to WQ_UNBOUND
>>> [   56.923226] workqueue: i915_hpd_poll_init_work [i915] hogged CPU for >10000us 4 times, consider switching to WQ_UNBOUND
>>> [   97.860430] workqueue: output_poll_execute [drm_kms_helper] hogged CPU for >10000us 8 times, consider switching to WQ_UNBOUND
>>> [   97.884453] workqueue: i915_hpd_poll_init_work [i915] hogged CPU for >10000us 8 times, consider switching to WQ_UNBOUND
>>>
>>> Adding WQ_UNBOUND to these queues didn't change the behavior.
>>
>> That should have made them go away as the code path isn't active at all for
>> WQ_UNBOUND workqueues. Can you please double check?
>>
>>> Maybe relevant: I run the affected system headless.
>>
>> i915 folks, workqueue recently added debug warnings which trigger when a
>> per-cpu work item hogs the CPU for too long - 10ms in this case. This is
>> problematic because such work item can stall other per-cpu work items.
>>
>> * Is it expected for the above two work functions to occupy the CPU for over
>>   10ms repeatedly?
> 
> No, this shouldn't happen.
> 
> I assume it happens in
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> 
> after cfd48ad8c4a9 ("drm/i915: Fix HPD polling, reenabling the output poll work as needed")
> 
> which could result in the above problem.
> 
> Could you give a try to
> https://lore.kernel.org/all/20230809104307.1218058-1-imre.deak@intel.com/
> 
> and if that doesn't help provide more information/logs, by opening a
> ticket at:
> https://gitlab.freedesktop.org/drm/intel/-/issues/new
> 
Done
https://gitlab.freedesktop.org/drm/intel/-/issues/9245

> Thanks,
> Imre
> 
>> * If so, can we make them use an unbound workqueue instead?
>>
>> Thanks.
>>
>> -- 
>> tejun