Quoting Tvrtko Ursulin (2019-01-31 09:19:18)
>
> On 30/01/2019 18:14, Chris Wilson wrote:
> > Quoting Tvrtko Ursulin (2019-01-30 18:05:42)
> >>> @@ -766,8 +774,10 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> >>> * second request, and so we never need to tell the
> >>> * hardware about the first.
> >>> */
> >>> - if (last &&
> >>> - !can_merge_ctx(rq->hw_context, last->hw_context)) {
> >>> + if (last && !can_merge_rq(last, rq)) {
> >>> + if (last->hw_context == rq->hw_context)
> >>> + goto done;
> >>
> >> I don't get this added check. AFAICS it will only trigger with GVT
> >> making it not consider filling both ports if possible.
> >
> > Because we are preparing for can_merge_rq() deciding not to merge the
> > same context. If we do that we can't continue on to the next port and
> > must terminate the loop, violating the trick with the hint in the
> > process.
> >
> > This changes due to the next patch, per-context freq and probably more
> > that I've forgotten.
>
> After a second look, I noticed the existing GVT comment a bit lower down
> which avoids populating port1 already.
>
> Maybe one thing which would make sense is to re-arange these checks in
> the order of "priority", like:
>
> if (last && !can_merge_rq(...)) {
> // naturally highest prio since it is impossible
> if (port == last_port)
> goto done;
> // 2nd highest to account for programming limitation
> else if (last->hw_context == rq->hw_context)
> goto done;
I was tempted to pull the last_port and context checks together.
> // GVT check simplified (I think - since we know last is either
> different ctx or single submit)
> else if (ctx_single_port_submission(rq->hw_context))
> goto done;
And that's what I think and I tried to get gvt to clarify that their
checks are excessive. And I'll keep on suggesting that they remove their
poking around inside the scheduler... :-p
But it's definitely something I want out of sight.
-Chris
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