[Intel-gfx] [PATCH v3] drm/i915: Optimistically spin for the request completion

[Chris Wilson]

On Thu, Mar 12, 2015 at 11:11:17AM +0000, Chris Wilson wrote:
> This provides a nice boost to mesa in swap bound scenarios (as mesa
> throttles itself to the previous frame and given the scenario that will
> complete shortly). It will also provide a good boost to systems running
> with semaphores disabled and so frequently waiting on the GPU as it
> switches rings. In the most favourable of microbenchmarks, this can
> increase performance by around 15% - though in practice improvements
> will be marginal and rarely noticeable.
> 
> v2: Account for user timeouts
> v3: Limit the spinning to a single jiffie (~1us) at most. On an
> otherwise idle system, there is no scheduler contention and so without a
> limit we would spin until the GPU is ready.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>

I'm really happy with this tradeoff. Can we throw this to the vultures
to see if anyone notices?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre