From mboxrd@z Thu Jan  1 00:00:00 1970
From: Daniel Vetter <daniel@ffwll.ch>
Subject: Re: [PATCH 2/2] drm/i915: add debugfs interface to
 control rc6 and rps
Date: Tue, 29 Nov 2011 15:12:50 +0100
Message-ID: <20111129140843.GA5667@phenom.ffwll.local>
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To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: intel-gfx@lists.freedesktop.org, Eugeni Dodonov <eugeni.dodonov@intel.com>
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On Tue, Nov 29, 2011 at 01:05:03PM +0000, Chris Wilson wrote:
> On Tue, 29 Nov 2011 10:55:05 -0200, Eugeni Dodonov <eugeni.dodonov@intel.com> wrote:
> > This allows to enable/disable rps and rc6 from userspace. This is
> > necessary for to have predictable results from hardware counters, and also
> > to provide a finer granularity over power control from userspace.
> 
> Reading registers and counters is handled with i915_forcewake_user. So
> the question is what benefit does htis give over module reload. It looks
> far riskier...

The observation architecture bspec says that we need to disable rc6,
otherwise we'll get garbage in the gpu perf counters. But imo I think this
should be handled in the kernel (we neeed to write tons of funny registers
to set things up anyway), at least for the time-based perf counter
sampling. For prototyping things with intel_reg_write disabling rc6 at
module load time seems sufficient to me.
-Daniel
-- 
Daniel Vetter
Mail: daniel@ffwll.ch
Mobile: +41 (0)79 365 57 48