Re: [PATCH 1/2] drm/i915: tune the RC6 threshold for stability

From: Daniel Vetter <daniel.vetter@ffwll.ch>
To: "Stéphane Marchesin" <marcheu@chromium.org>
Cc: intel-gfx <intel-gfx@lists.freedesktop.org>
Subject: Re: [PATCH 1/2] drm/i915: tune the RC6 threshold for stability
Date: Fri, 14 Jun 2013 21:32:09 +0200	[thread overview]
Message-ID: <CAKMK7uGp7JzLyFacG39+epM12hE8GfxxpjdnqPj3EjWzYbwTSQ@mail.gmail.com> (raw)
In-Reply-To: <CADMs+9aqQ1hWF1W5wwg9JquKg2vFG_ZyUjiVkojNN3GedTykGQ@mail.gmail.com>

On Fri, Jun 14, 2013 at 9:13 PM, Stéphane Marchesin
<marcheu@chromium.org> wrote:
> On Wed, Jun 12, 2013 at 2:41 AM, Chris Wilson <chris@chris-wilson.co.uk> wrote:
>> On Tue, Jun 11, 2013 at 03:49:26PM -0700, Stéphane Marchesin wrote:
>>> It's basically the same deal as the RC6+ issues on ivy bridge
>>> except this time with RC6 on sandy bridge. Like last time the
>>> core of the issue is that the timings don't work 100% with our
>>> voltage regulator. So from time to time, the kernel will print
>>> a warning message about the GPU not getting out of RC6. In
>>> particular, I found this fairly easy to reproduce during
>>> suspend/resume.
>>>
>>> Changing the threshold to 150000 instead of 50000 seems to fix
>>> the issue.
>>>
>>> I also measured the idle power usage before/after this patch and
>>> didn't see a difference on a sandy bridge laptop.
>>>
>>> Signed-off-by: Stéphane Marchesin <marcheu@chromium.org>
>>
>> One magic number for another with no idea what is blowing up - I fear we
>> are just changing the frequency of the hang. I've pinged a number of snb
>> rc6 bug reports to see if we get a bite.
>
> Yup, if only Intel documented those registers :)

We've spammed rc6 bugs in bugzilla, one reporter says that this patch
breaks rc6 from "sometimes it doesn't work after resume" to "always
broken":

https://bugs.freedesktop.org/show_bug.cgi?id=54089#c63

So I guess I can't merge this :(
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch