Re: [Intel-gfx] [PATCH 02/10] drm/i915/gt: Always check to enable timeslicing if not submitting

From: Mika Kuoppala <mika.kuoppala@linux.intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>, intel-gfx@lists.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH 02/10] drm/i915/gt: Always check to enable timeslicing if not submitting
Date: Fri, 05 Jun 2020 18:34:52 +0300	[thread overview]
Message-ID: <87lfl1a5lv.fsf@gaia.fi.intel.com> (raw)
In-Reply-To: <159137114732.22562.14510475315266373484@build.alporthouse.com>

Chris Wilson <chris@chris-wilson.co.uk> writes:

> Quoting Mika Kuoppala (2020-06-05 16:20:34)
>> Chris Wilson <chris@chris-wilson.co.uk> writes:
>> 
>> > We may choose not to submit for a number of reasons, yet not fill both
>> > ELSP. In which case we must start timeslicing (there will be no ACK
>> > event on which to hook the start) if the queue would benefit from the
>> > currently active context being evicted.
>> >
>> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>> > ---
>> >  drivers/gpu/drm/i915/gt/intel_lrc.c | 5 ++---
>> >  1 file changed, 2 insertions(+), 3 deletions(-)
>> >
>> > diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
>> > index 92c3368ffcbd..d55a5e0466e5 100644
>> > --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
>> > +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
>> > @@ -2362,10 +2362,8 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>> >                               if (last->context == rq->context)
>> >                                       goto done;
>> >  
>> > -                             if (i915_request_has_sentinel(last)) {
>> > -                                     start_timeslice(engine, rq_prio(rq));
>> > +                             if (i915_request_has_sentinel(last))
>> >                                       goto done;
>> > -                             }
>> >  
>> >                               /*
>> >                                * If GVT overrides us we only ever submit
>> > @@ -2446,6 +2444,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>> >               set_preempt_timeout(engine, *active);
>> >               execlists_submit_ports(engine);
>> >       } else {
>> > +             start_timeslice(engine, execlists->queue_priority_hint);
>> 
>> If we ended up with same set of request, we want to skip submitting.
>> But why would we want to skip timeslicing?
>
> Because we have already submitted the exact same pair of requests
> and so there will a be a set_timeslice() either pending or have taken
> place. In particular, we wanted to stop timeslicing if after a timeslice
> expiry we submitted exactly the same requests as before the timelice --
> we know that until the arrival of a new request that there is no need
> for a new timeslice, that will just result in the same pair being
> submitted in order each time.

Makes sense. I managed look over the set_timeslice.

Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>

> -Chris
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