linux-kernel - Re: Intel graphics CPU usage

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Message-ID: <AANLkTinfYBC0=DOzWaGD0DrGH8+M_rFRtuzHrM4yjRxx@mail.gmail.com>
Date:	Sun, 15 Aug 2010 21:27:28 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andy Lutomirski <luto@...ealbox.com>
Cc:	Dave Airlie <airlied@...ux.ie>,
	Chris Wilson <chris@...is-wilson.co.uk>,
	Zhao Yakui <yakui.zhao@...el.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Adam Jackson <ajax@...hat.com>,
	DRI mailing list <dri-devel@...ts.freedesktop.org>,
	linux-kernel@...r.kernel.org
Subject: Re: Intel graphics CPU usage - SDVO detect bogosity?

On Sun, Aug 15, 2010 at 9:06 PM, Andy Lutomirski <luto@...ealbox.com> wrote:
>
> You might be hitting the infamous hotplug storm [1].  The symptoms vary by
> kernel version.

Hmm. I don't think it's a storm. The drm.debug=4 thing shows things
just every 10 seconds. That seems pretty controlled.

Of course, it seems to be several milliseconds worth of work then, so
it's not _too_ controlled. I must be missing some detail.

> If I'm right, the outputs of intel_bios_dumper and intel_bios_reader could
> be instructive (both are in intel-gpu-tools).

My version of intel-gpu-tools must be old (fedora 12). It has
intel_gpu_dump and intel_reg_write and some other apps, but not the
bios-dumper/reader.

Not that I could read the output of them anyway, I bet ;)

> You could also try intel_reg_write 0x61110 0x0 and see if the problem stops
> (at least until a suspend/resume cycle).  That command turns off output
> hotplug on the card, which has the side effect that the kernel will stop
> acting on bogus interrupts.

  # intel_reg_write 0x61110 0x0
  Value before: 0x4000220
  Value after: 0x0

but it doesn't seem to change any behavior. Still that sdvo probe
every 10 s, and still 1% of CPU for kworker in top. But that kworker
thing definitely has to be separate from the 10-second sdvo probe,
because it shows up all the time (ie top updates every second).

But right now the wife is using that machine, so I can't check the "it
should be totally idle, what the heck is going on" behavior at the
moment.

                Linus

                          Linus
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