Re: [PATCH] drm/i915: Make sample_c messages go faster on Haswell.

[Kenneth Graunke <kenneth@whitecape.org>]

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On Monday, January 05, 2015 02:19:15 PM Daniel Vetter wrote:
> On Wed, Dec 31, 2014 at 04:23:00PM -0800, Kenneth Graunke wrote:
> > Haswell significantly improved the performance of sampler_c messages,
> > but the optimization appears to be off by default.  Later platforms
> > remove this bit, and apparently always enable the optimization.
> > 
> > Improves performance in "Counter Strike: Global Offensive" by 18%
> > at default settings on Iris Pro.
> > 
> > This may break sampling of paletted formats (P8/A8P8/P8A8).  It's
> > unclear whether it affects sampling of paletted formats in general,
> > or just the sample_c message (which is never used).
> > 
> > While libva does have support for using paletted formats (primarily
> > for OSDs), that support appears to have been broken for at least a
> > year, so I couldn't observe a regression from this.
> > 
> > Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
> > ---
> >  drivers/gpu/drm/i915/i915_reg.h | 1 +
> >  drivers/gpu/drm/i915/intel_pm.c | 4 ++++
> >  2 files changed, 5 insertions(+)
> > 
> > Resubmitting the patch to unconditionally enable this.  I tried to get
> > libva-intel to use paletted formats, and observe a regression...but the
> > only thing I found that used it was mplayer's OSD (on screen display).
> > Even without my patch, the colors were totally wrong with that, and it's
> > according to a few distro wikis, that's been the case for over a year.
> > 
> > If libva's code for paletted formats /is/ broken, they could always add
> > code to disable this bit using the command validator when fixing it.
> > 
> > Could we try merging this, and back it out if someone reports a
> > regression?  I haven't observed any problems.  It's also been quite
> > stable.
> 
> Yeah makes sense. When resending please incorporated review feedback
> (Ville dug out the wa name), I've done that. And I've pasted the
> additional detail about the libva saga, just for reference (since no one
> will remember that it's mplayer's OSD which uses this 2 months down the
> road).
> 
> Also please cc libva mailing lists next time around as an fyi. Done that
> too.
> 
> Queued for -next, thanks for the patch.
> -Daniel

Oh, sorry, I missed that in the review.

Thanks, Daniel!

--Ken

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