Re: [PATCH v2 3/7] drm/i915/execlists: Make submission tasklet hardirq safe

[Chris Wilson <chris@chris-wilson.co.uk>]

Quoting Tvrtko Ursulin (2018-05-08 11:56:37)
> 
> On 08/05/2018 11:24, Chris Wilson wrote:
> > Quoting Tvrtko Ursulin (2018-05-08 11:10:41)
> >> On 07/05/2018 14:57, Chris Wilson wrote:
> >>> @@ -744,13 +748,25 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> >>>        /* We must always keep the beast fed if we have work piled up */
> >>>        GEM_BUG_ON(execlists->first && !port_isset(execlists->port));
> >>>    
> >>> -unlock:
> >>> -     spin_unlock_irq(&engine->timeline.lock);
> >>> -
> >>> -     if (submit) {
> >>> +     /* Re-evaluate the executing context setup after each preemptive kick */
> >>> +     if (last)
> >>>                execlists_user_begin(execlists, execlists->port);
> >>
> >> Last can be non-null and submit false, so this is not equivalent.
> >>
> >> By the looks of it makes no difference since it is OK to set the
> >> execlists user active bit multiple times. Even though the helper is
> >> called execlists_set_active_once. But the return value is not looked at.
> >>
> >> Still, why not keep doing this when submit is true?
> > 
> > It's a subtle difference, in that we want the context reevaluated every
> > time we kick the queue as we may have changed state that we want to
> > reload, and not just ELSP. Sometimes we need inheritance of more than
> > just priority...
> 
> What do you mean by context re-evaluated?
> 
> ACTIVE_USER is set from first to last request, no? I don't understand 
> what would change if you would set it multiple times while it is already 
> set.

It's not about ACTIVE_USER. This is a hook to indicate a change in
context state being executed on the GPU. It's to be hooked into by the
cpufreq/pstate code, gpufreq code, etc. Later realisation is that they
need to be notified for all context changes here.
-Chris
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