Re: [Intel-gfx] [PATCH 4/4] drm/i915/gt: Remove timeslice suppression

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 06/01/2021 16:08, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2021-01-06 15:57:49)

[snip]

>>> @@ -1363,16 +1336,16 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>>>                        __unwind_incomplete_requests(engine);
>>>    
>>>                        last = NULL;
>>> -             } else if (need_timeslice(engine, last) &&
>>> -                        timeslice_expired(execlists, last)) {
>>> +             } else if (timeslice_expired(engine, last)) {
>>>                        ENGINE_TRACE(engine,
>>> -                                  "expired last=%llx:%lld, prio=%d, hint=%d, yield?=%s\n",
>>> -                                  last->fence.context,
>>> -                                  last->fence.seqno,
>>> -                                  last->sched.attr.priority,
>>> +                                  "expired:%s last=%llx:%lld, prio=%d, hint=%d, yield?=%s\n",
>>> +                                  yesno(timer_expired(&execlists->timer)),
>>> +                                  last->fence.context, last->fence.seqno,
>>> +                                  rq_prio(last),
>>>                                     execlists->queue_priority_hint,
>>>                                     yesno(timeslice_yield(execlists, last)));
>>>    
>>> +                     cancel_timer(&execlists->timer);
>>
>> What is this cancel for?
> 
> This branch is taken upon yielding the timeslice, but we may not submit
> a new pair of contexts, leaving the timer active (and marked as
> expired). Since the timer remains expired, we will continuously looped
> until a context switch, or some other preemption event.

Sorry I was looking at the cancel_timer in process_csb and ended up 
replying at the wrong spot. The situation there seems to be removing the 
single timeslice related call (set_timeslice) and adding a cancel_timer 
which is also not obvious to me what it is about.

Regards,

Tvrtko
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