[Intel-gfx] [PATCH 07/16] drm/i915/gt: Check for a completed last request once

[Tvrtko Ursulin]

On 24/11/2020 17:38, Chris Wilson wrote:
> 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 at chris-wilson.co.uk>
>>> ---
>>>    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.

Okay, if you mention that in the commit message you can add my rb.

Regards,

Tvrtko