[Intel-gfx] [PATCH 2/3] drm/i915/gem: Treat submit-fence as weak dependency for new clients

[Chris Wilson]

Quoting Tvrtko Ursulin (2020-05-07 15:59:56)
> 
> On 07/05/2020 09:21, Chris Wilson wrote:
> > The submit-fence adds a weak dependency to the requests, and for the
> > purpose of our FQ_CODEL hinting we do not want to treat as a
> > restriction. This is primarily because clients may treat submit-fences
> > as a bidirectional bonding between a pair of co-ordinating requests.
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > ---
> >   drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 13 ++++++++++++-
> >   1 file changed, 12 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> > index 966523a8503f..e8bf0cf02fd7 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> > @@ -2565,6 +2565,17 @@ static void retire_requests(struct intel_timeline *tl, struct i915_request *end)
> >                       break;
> >   }
> >   
> > +static bool new_client(struct i915_request *rq)
> > +{
> > +     struct i915_dependency *p;
> > +
> > +     list_for_each_entry(p, &rq->sched.signalers_list, signal_link)
> > +             if (!(p->flags & I915_DEPENDENCY_WEAK))
> > +                     return false;
> > +
> > +     return true;
> > +}
> > +
> >   static void eb_request_add(struct i915_execbuffer *eb)
> >   {
> >       struct i915_request *rq = eb->request;
> > @@ -2604,7 +2615,7 @@ static void eb_request_add(struct i915_execbuffer *eb)
> >                * Allow interactive/synchronous clients to jump ahead of
> >                * the bulk clients. (FQ_CODEL)
> >                */
> > -             if (list_empty(&rq->sched.signalers_list))
> > +             if (new_client(rq))
> >                       attr.priority |= I915_PRIORITY_WAIT;
> >       } else {
> >               /* Serialise with context_close via the add_to_timeline */
> > 
> 
> Did absence of this have any functional effect? I hope not, but anyway:

Bah, I have a new test case where this WAIT bumping is still upsetting us.

I don't think I have any choice but to rip it out if we have timeslicing
enabled.

Would you prefer a complete remission of I915_PRIORITY_WAIT or keep it
under if (!intel_engine_has_timeslicing(rq->engine)) ?
-Chris