[Intel-gfx] [PATCH] drm/i915: Add background commentary to "waitboosting"

Chris Wilson chris at chris-wilson.co.uk
Fri Dec 11 13:03:36 PST 2015

On Fri, Dec 11, 2015 at 07:24:29PM +0100, Daniel Vetter wrote:
> On Thu, Dec 10, 2015 at 10:37:36AM +0000, Chris Wilson wrote:
> > Describe the intent of boosting the GPU frequency to maximum before
> > waiting on the GPU.
> > 
> > RPS waitboosting was introduced with
> > 
> > commit b29c19b645287f7062e17d70fa4e9781a01a5d88
> > Author: Chris Wilson <chris at chris-wilson.co.uk>
> > Date:   Wed Sep 25 17:34:56 2013 +0100
> > 
> >     drm/i915: Boost RPS frequency for CPU stalls
> > 
> > but lacked a concise comment in the code to explain itself.
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> We might want to consolidate this with the kerneldoc for gen6_rps_boost,
> if that ever happens. But for now this is a good place.

You should end up with both. The function comment will explain what it
does and give reasons why you might want to call it (clients stalls,
detecting missed pageflips, etc), but this code comment should explain
the intent of calling it now. I was tempted to try and put forward some
more objective figures for the benefits of waitboosting, but they grow
stale very quickly so I went with the long winded commentary instead.

Chris Wilson, Intel Open Source Technology Centre

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