linux-kernel - Re: Why is kslowd accumulating so much CPU time?

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Message-ID: <AANLkTimTAqERLRx-eSpbeXXwMh3K9f8FaZOeNY-oNmdL@mail.gmail.com>
Date:	Wed, 16 Jun 2010 14:33:31 +0100
From:	Andy Whitcroft <apw@...onical.com>
To:	David Howells <dhowells@...hat.com>
Cc:	tytso@....edu, Dave Airlie <airlied@...il.com>,
	Dave Airlie <airlied@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: Why is kslowd accumulating so much CPU time?

On Wed, Jun 16, 2010 at 12:37 PM, Andy Whitcroft <apw@...onical.com> wrote:
>> Can you see what they're doing?
>>
>>        watch -n0 cat /sys/kernel/debug/slow_work/runqueue
>
> Turned on the debugging and applied the patch from Ted, and when
> things are bad I see constant cycling of all four threads in the
> output showing similar to the below, note only one thread shows at a
> time:
>
> Every 0.1s: cat /sys/kernel/debug/slow_work/runqueue    Wed Jun 16 12:34:52 2010
>
> THR PID   ITEM ADDR        FL MARK  DESC
> === ===== ================ == ===== ==========
>   0   897 ffff88012bb07510 12  20ms DRM_CRTC_HELPER: i915@pci:0000:00:02.0
>
> When things are working well I see the same output appearing for one
> update, about every 10s.

Ok I've added some additional debug and these appear to be being
thrown a loop by the HPD interrupt which is firing continiusly, here
is a sample from some 4 minutes after boot:

[  284.862670] APW: drm_helper_hpd_irq_event: cancel/submit
[  284.882803] APW: drm_helper_hpd_irq_event: cancel/submit
[  284.902691] APW: drm_helper_hpd_irq_event: cancel/submit
[  284.922814] APW: drm_helper_hpd_irq_event: cancel/submit
[  284.942620] APW: drm_helper_hpd_irq_event: cancel/submit
[  284.962707] APW: drm_helper_hpd_irq_event: cancel/submit
[  284.982937] APW: drm_helper_hpd_irq_event: cancel/submit
[  285.004181] APW: drm_helper_hpd_irq_event: cancel/submit
[  285.022622] APW: drm_helper_hpd_irq_event: cancel/submit
[  285.042569] APW: drm_helper_hpd_irq_event: cancel/submit
[  285.062593] APW: drm_helper_hpd_irq_event: cancel/submit
[  285.082683] APW: drm_helper_hpd_irq_event: cancel/submit

Later when things calm down we see them but much much less often:

[  379.038239] APW: drm_helper_hpd_irq_event: cancel/submit
[  379.044904] APW: drm_helper_hpd_irq_event: cancel/submit
[  382.438106] APW: drm_helper_hpd_irq_event: cancel/submit
[  382.444754] APW: drm_helper_hpd_irq_event: cancel/submit
[  385.838072] APW: drm_helper_hpd_irq_event: cancel/submit
[  385.844735] APW: drm_helper_hpd_irq_event: cancel/submit
[  389.237876] APW: drm_helper_hpd_irq_event: cancel/submit
[  389.244523] APW: drm_helper_hpd_irq_event: cancel/submit
[  392.638048] APW: drm_helper_hpd_irq_event: cancel/submit
[  392.644740] APW: drm_helper_hpd_irq_event: cancel/submit

-apw
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