[Intel-gfx] [PATCH 01/11] drm/i915/execlists: Avoid kicking the submission too early for rescheduling

[Chris Wilson]

Quoting Mika Kuoppala (2018-03-27 13:18:06)
> Chris Wilson <chris at chris-wilson.co.uk> writes:
> 
> > Quoting Mika Kuoppala (2018-03-27 12:34:31)
> >> Chris Wilson <chris at chris-wilson.co.uk> writes:
> >> 
> >> > If the request is still waiting on external fences, it has not yet been
> >> > submitted to the HW queue and so we can forgo kicking the submission
> >> > tasklet when re-evaluating its priority.
> >> >
> >> > This should have no impact other than reducing the number of tasklet
> >> > wakeups under signal heavy workloads (e.g. switching between engines).
> >> >
> >> > v2: Use prebaked container_of()
> >> >
> >> > References: f6322eddaff7 ("drm/i915/preemption: Allow preemption between submission ports")
> >> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> >> > Cc: Michał Winiarski <michal.winiarski at intel.com>
> >> > Cc: Michel Thierry <michel.thierry at intel.com>
> >> > Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> >> > Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> >> > ---
> >> >  drivers/gpu/drm/i915/intel_lrc.c | 15 +++++++++++----
> >> >  1 file changed, 11 insertions(+), 4 deletions(-)
> >> >
> >> > diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> >> > index b4ab06b05e58..104b69e0494f 100644
> >> > --- a/drivers/gpu/drm/i915/intel_lrc.c
> >> > +++ b/drivers/gpu/drm/i915/intel_lrc.c
> >> > @@ -1051,12 +1051,16 @@ static void queue_request(struct intel_engine_cs *engine,
> >> >       list_add_tail(&pt->link, &lookup_priolist(engine, pt, prio)->requests);
> >> >  }
> >> >  
> >> > -static void submit_queue(struct intel_engine_cs *engine, int prio)
> >> > +static void __submit_queue(struct intel_engine_cs *engine, int prio)
> >> >  {
> >> > -     if (prio > engine->execlists.queue_priority) {
> >> >               engine->execlists.queue_priority = prio;
> >> >               tasklet_hi_schedule(&engine->execlists.tasklet);
> >> > -     }
> >> > +}
> >> > +
> >> > +static void submit_queue(struct intel_engine_cs *engine, int prio)
> >> > +{
> >> > +     if (prio > engine->execlists.queue_priority)
> >> > +             __submit_queue(engine, prio);
> >> 
> >> You did this...
> >> 
> >> >  }
> >> >  
> >> >  static void execlists_submit_request(struct i915_request *request)
> >> > @@ -1189,7 +1193,10 @@ static void execlists_schedule(struct i915_request *request, int prio)
> >> >                       __list_del_entry(&pt->link);
> >> >                       queue_request(engine, pt, prio);
> >> >               }
> >> > -             submit_queue(engine, prio);
> >> > +
> >> > +             if (prio > engine->execlists.queue_priority &&
> >> > +                 i915_sw_fence_done(&pt_to_request(pt)->submit))
> >> > +                     __submit_queue(engine, prio);
> >> 
> >> ..to have explicit priority comparison on submit callsite I gather.
> >> Or is there some other reason?
> >
> > No, just because I wanted both checks in this case. On the other path
> > i915_sw_fence_done() isn't technically true as we are in process of
> > performing the i915_sw_fence callback, so just i915_sw_fence_signaled().
> > But we don't want to use i915_sw_fence_signaled() here as I don't want
> > to think about the race. :)
> >
> > So since prio > engine.queue_priority should be cheaper than loading the
> > cacheline for the request->submit.flags, I wanted that tested first as
> > it will only fire, at most, once per engine.
> 
> Ok, didn't see the perf angle of it but makes sense.
> 
> Reviewed-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>

Fixed up the double indent and pushed. Thanks for the review, and
digging into i915_sw_fence :)
-Chris