Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
> If we stop filling the ELSP due to an incompatible virtual engine
> request, check if we should enable the timeslice on behalf of the queue.
>
> This fixes the case where we are inspecting the last->next element when
> we know that the last element is the last request in the execution queue,
> and so decided we did not need to enable timeslicing despite the intent
> to do so!
>
> Fixes: 8ee36e048c98 ("drm/i915/execlists: Minimalistic timeslicing")
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # v5.4+
Reviewed-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/gt/intel_lrc.c | 29 ++++++++++++++++++-----------
> 1 file changed, 18 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index 13941d1c0a4a..a1d268880cfe 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -1757,11 +1757,9 @@ need_timeslice(struct intel_engine_cs *engine, const struct i915_request *rq)
> if (!intel_engine_has_timeslices(engine))
> return false;
>
> - if (list_is_last(&rq->sched.link, &engine->active.requests))
> - return false;
> -
> - hint = max(rq_prio(list_next_entry(rq, sched.link)),
> - engine->execlists.queue_priority_hint);
> + hint = engine->execlists.queue_priority_hint;
> + if (!list_is_last(&rq->sched.link, &engine->active.requests))
> + hint = max(hint, rq_prio(list_next_entry(rq, sched.link)));
>
> return hint >= effective_prio(rq);
> }
> @@ -1803,6 +1801,18 @@ static void set_timeslice(struct intel_engine_cs *engine)
> set_timer_ms(&engine->execlists.timer, active_timeslice(engine));
> }
>
> +static void start_timeslice(struct intel_engine_cs *engine)
> +{
> + struct intel_engine_execlists *execlists = &engine->execlists;
> +
> + execlists->switch_priority_hint = execlists->queue_priority_hint;
> +
> + if (timer_pending(&execlists->timer))
> + return;
> +
> + set_timer_ms(&execlists->timer, timeslice(engine));
> +}
> +
> static void record_preemption(struct intel_engine_execlists *execlists)
> {
> (void)I915_SELFTEST_ONLY(execlists->preempt_hang.count++);
> @@ -1966,11 +1976,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> * Even if ELSP[1] is occupied and not worthy
> * of timeslices, our queue might be.
> */
> - if (!execlists->timer.expires &&
> - need_timeslice(engine, last))
> - set_timer_ms(&execlists->timer,
> - timeslice(engine));
> -
> + start_timeslice(engine);
> return;
> }
> }
> @@ -2005,7 +2011,8 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>
> if (last && !can_merge_rq(last, rq)) {
> spin_unlock(&ve->base.active.lock);
> - return; /* leave this for another */
> + start_timeslice(engine);
> + return; /* leave this for another sibling */
> }
>
> ENGINE_TRACE(engine,
> --
> 2.25.1
