[Intel-gfx] [PATCH] tests/pm_rps: Add a new testcase to provoke the "stuck at max" bug

[Daniel Vetter]

On Thu, Mar 27, 2014 at 3:19 AM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> On Wed, Mar 26, 2014 at 10:17:51PM +0100, Daniel Vetter wrote:
>> Note that the sleep(5); to fully idle the gpu is _really_ important.
>> Without it the bug is not exhibited.
>>
>> The issue at hand is that after gem_quiescent_gpu we are at max
>> (expected, since the blocking waits peg to max), but then we never go
>> down to a lower freq again until we're fully idle. The tiny load is
>> sufficient to keep the gpu at max. I've played around with this a bit
>> and even ridiculously low loads (like one MI_STORE per 50ms) are
>> enough to keep the gpu at max freq.
>
> commit 2754436913b94626a5414d82f0996489628c513d
> Author: Deepak S <deepak.s at intel.com>
> Date:   Mon Jan 27 21:35:05 2014 +0530
>
>     drm/i915: Disable/Enable PM Intrrupts based on the current freq.
>
> as expected is complete and utter codswallop.

I can confirm that reverting this plus it's vlv deps gets
igt/pm_rps/blocking going again. The gpu isn't pegged to max any more
like with current -nightly.

Deepak? I guess this might explain why the boost logic gives sometimes
inferior power numbers ... Note: Since this is a regression it counts
as high-prio for upstream business ;-)
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch