[Intel-gfx] [PATCH 2/2] drm/i915: tune the RC6 threshold for stability

[Daniel Vetter]

On Tue, Aug 13, 2013 at 10:29 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Tue, Aug 13, 2013 at 11:55:17AM -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 125000 instead of 50000 seems to fix
>> the issue. The previous patch used 150000 but as it turns out
>> this doesn't work everywhere. After getting such a machine, I
>> bisected the highest value which works, which is 125000, so here
>> it is.
>>
>> I also measured the idle power usage before/after this patch and
>> didn't see a difference on a sandy bridge laptop. On haswell and
>> up, it makes a big difference, so we want to keep it at 50k
>> there. It also seems like haswell doesn't have the RC6 issues
>> that sandy bridge has so the 50k value is fine.
>>
>> Signed-off-by: Stéphane Marchesin <marcheu at chromium.org>
> Queued for -next, thanks for the patch.

And it blew up:

https://bugs.freedesktop.org/show_bug.cgi?id=71656

What do? We probably need a sysfs knob for this crap. Presuming no one
has a brilliant idea I'll queue the revert next week.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch