[Intel-gfx] [PATCH 07/31] drm/i915/execlists: Direct submission of new requests (avoid tasklet/ksoftirqd)

[Chris Wilson]

Quoting Tvrtko Ursulin (2018-06-27 16:21:24)
> 
> On 27/06/2018 14:29, Chris Wilson wrote:
> > Quoting Tvrtko Ursulin (2018-06-27 14:15:22)
> >>
> >> On 27/06/2018 11:58, Chris Wilson wrote:
> >>> That tasklets get kicked randomly, I think was the culprit.
> >>
> >> What do you mean? I hope we have busy-idle quite controlled and we know
> >> when we should and should expect a tasklet. If we synced them when
> >> transitioning to idle they cannot happen. Otherwise we better be active!
> >> GEM_BUG_ON(!engine->i915->gt.awake) instead? Does that trigger?!
> > 
> > tasklet_schedule() is called off the main path, without locking, so
> > unsynchronized to parking. Just because.
> 
> I need to understand this - which main path? Submission - we will be 
> mark_busy. After last request - we will idle the engines and sync the 
> tasklet.

There's a bonus kick in intel_engine_is_idle() (behind an unprotected
read of active, so still possible to race), and I've added an
unconditional kick to pmu_enable because we play games with
tasklet_disable there that may cause us to miss a direct submission.
-Chris