Re: [PATCH 16/17] RFM drm/i915: Boost RPS frequency for CPU stalls

Chris Wilson
2013-08-26T22:56:28Z

On Mon, Aug 26, 2013 at 07:51:08PM -0300, Rodrigo Vivi wrote:
> From: Chris Wilson <chris@chris-wilson.co.uk>
>
> If we encounter a situation where the CPU blocks waiting for results
> from the GPU, give the GPU a kick to boost its the frequency.
>
> This should work to reduce user interface stalls and to quickly promote
> mesa to high frequencies - but the cost is that our requested frequency
> stalls high (as we do not idle for long enough before rc6 to start
> reducing frequencies, nor are we aggressive at down clocking an
> underused GPU). However, this should be mitigated by rc6 itself powering
> off the GPU when idle, and that energy use is dependent upon the workload
> of the GPU in addition to its frequency (e.g. the math or sampler
> functions only consume power when used). Still, this is likely to
> adversely affect light workloads.
>
> Stéphane raised the concern that this will punish good applications and
> reward bad applications - but due to the nature of how mesa performs its
> client throttling, I believe all mesa applications will be roughly
> equally affected.
>
> RFM - request for measurement!
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Kenneth Graunke <kenneth@whitecape.org>
> Cc: Stéphane Marchesin <stephane.marchesin@gmail.com>
> Cc: "Meng, Mengmeng" <mengmeng.meng@intel.com>
> Cc: "Zhuang, Lena" <lena.zhuang@intel.com>

This patch is superseded by later versions.
-Chris

--
Chris Wilson, Intel Open Source Technology Centre