drm/i915: Optimistically spin for the request completion
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. v4: Drop forcewake - the lazy coherent access doesn't require it, and we have no reason to believe that the forcewake itself improves seqno coherency - it only adds delay. Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Eero Tamminen <eero.t.tamminen@intel.com> Cc: "Rantala, Valtteri" <valtteri.rantala@intel.com> Reviewed-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com> Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
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