Quoting Tvrtko Ursulin (2020-11-24 17:19:23)
>
> On 24/11/2020 11:42, Chris Wilson wrote:
> > Pull the repeated check for the last active request being completed to a
> > single spot, when deciding whether or not execlist preemption is
> > required.
> >
> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/gt/intel_lrc.c | 15 ++++-----------
> > 1 file changed, 4 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> > index cf11cbac241b..43703efb36d1 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> > @@ -2141,12 +2141,9 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> > */
> >
> > if ((last = *active)) {
> > - if (need_preempt(engine, last, rb)) {
> > - if (i915_request_completed(last)) {
> > - tasklet_hi_schedule(&execlists->tasklet);
> > - return;
> > - }
> > -
> > + if (i915_request_completed(last)) {
> > + goto check_secondary;
> > + } else if (need_preempt(engine, last, rb)) {
> > ENGINE_TRACE(engine,
> > "preempting last=%llx:%lld, prio=%d, hint=%d\n",
> > last->fence.context,
> > @@ -2174,11 +2171,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> > last = NULL;
> > } else if (need_timeslice(engine, last, rb) &&
> > timeslice_expired(execlists, last)) {
> > - if (i915_request_completed(last)) {
> > - tasklet_hi_schedule(&execlists->tasklet);
> > - return;
> > - }
> > -
> > ENGINE_TRACE(engine,
> > "expired last=%llx:%lld, prio=%d, hint=%d, yield?=%s\n",
> > last->fence.context,
> > @@ -2214,6 +2206,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> > * we hopefully coalesce several updates into a single
> > * submission.
> > */
> > +check_secondary:
> > if (!list_is_last(&last->sched.link,
> > &engine->active.requests)) {
>
> Is there a tasklet_hi_schedule in here? I see set_timeslice in my checkout.
That tasklet_hi_schedule() was a mistake. It just devolves into a
busy-spinner as we wait for HW to send the next event, which turns out
not to be as instantaneous as hoped.
I recall leaving the imprint of my palm on my face when I figured out
what was causing the spike in the profile.
-Chris
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