Quoting Mika Kuoppala (2020-06-05 16:20:34)
> Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxx>
> > ---
> > 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.
-Chris
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