[Intel-gfx] [PATCH] drm/i915/execlists: Tweak virtual unsubmission

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-10-14 10:34:31)
> 
> On 13/10/2019 21:30, Chris Wilson wrote:
> > Since commit e2144503bf3b ("drm/i915: Prevent bonded requests from
> > overtaking each other on preemption") we have restricted requests to run
> > on their chosen engine across preemption events. We can take this
> > restriction into account to know that we will want to resubmit those
> > requests onto the same physical engine, and so can shortcircuit the
> > virtual engine selection process and keep the request on the same
> > engine during unwind.
> > 
> > References: e2144503bf3b ("drm/i915: Prevent bonded requests from overtaking each other on preemption")
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > ---
> >   drivers/gpu/drm/i915/gt/intel_lrc.c | 6 +++---
> >   drivers/gpu/drm/i915/i915_request.c | 2 +-
> >   2 files changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> > index e6bf633b48d5..03732e3f5ec7 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> > @@ -895,7 +895,6 @@ __unwind_incomplete_requests(struct intel_engine_cs *engine)
> >       list_for_each_entry_safe_reverse(rq, rn,
> >                                        &engine->active.requests,
> >                                        sched.link) {
> > -             struct intel_engine_cs *owner;
> >   
> >               if (i915_request_completed(rq))
> >                       continue; /* XXX */
> > @@ -910,8 +909,7 @@ __unwind_incomplete_requests(struct intel_engine_cs *engine)
> >                * engine so that it can be moved across onto another physical
> >                * engine as load dictates.
> >                */
> > -             owner = rq->hw_context->engine;
> > -             if (likely(owner == engine)) {
> > +             if (likely(rq->execution_mask == engine->mask)) {
> >                       GEM_BUG_ON(rq_prio(rq) == I915_PRIORITY_INVALID);
> >                       if (rq_prio(rq) != prio) {
> >                               prio = rq_prio(rq);
> > @@ -922,6 +920,8 @@ __unwind_incomplete_requests(struct intel_engine_cs *engine)
> >                       list_move(&rq->sched.link, pl);
> >                       active = rq;
> >               } else {
> > +                     struct intel_engine_cs *owner = rq->hw_context->engine;
> 
> I guess there is some benefit in doing fewer operations as long as we 
> are fixing the engine anyway (at the moment at least).

It also added a bit of consistency to how we detect virtual engine
during i915_request construction (e.g. __i915_request_add_to_timeline),
I liked that.
-Chris