[Intel-gfx] [PATCH] drm/i915: Truly bump ready tasks ahead of busywaits

[Chris Wilson]

Quoting Chris Wilson (2019-05-09 21:51:54)
> In commit b7404c7ecb38 ("drm/i915: Bump ready tasks ahead of
> busywaits"), I tried cutting a corner in order to not install a signal
> for each of our dependencies, and only listened to requests on which we
> were intending to busywait. The compromise that was made was that
> instead of then being able to promite the request with a full
> NOSEMAPHORE like its non-busywaiting brethren, as we had not ensured we
> had cleared the semaphore chain, we settled for only using the NEWCLIENT
> boost. With an over saturated system with multiple NEWCLIENTS in flight
> at any time, this was found to be an inadequate promotion and left us
> with a much poorer scheduling order than prior to using semaphores.
> 
> The outcome of this patch, is that all requests have NOSEMAPHORE
> priority when they have no dependencies and are ready to run and not
> busywait, restoring the pre-semaphore ordering on saturated systems.
> 
> Fixes: b7404c7ecb38 ("drm/i915: Bump ready tasks ahead of busywaits")

Fixes: f9e9e9de58c7 ("drm/i915: Prioritise non-busywait semaphore workloads")

> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Cc: Dmitry Rogozhkin <dmitry.v.rogozhkin at intel.com>
> Cc: Dmitry Ermilov <dmitry.ermilov at intel.com>