Quoting Tvrtko Ursulin (2019-11-27 14:22:37) > > On 27/11/2019 14:04, Chris Wilson wrote: > > Quoting Tvrtko Ursulin (2019-11-27 13:46:14) > >> On 27/11/2019 11:17, Chris Wilson wrote: > >>> We want the bonded request to have the same scheduler properties as its > >>> master so that it is placed at the same depth in the queue. For example, > >>> consider we have requests A, B and B', where B & B' are a bonded pair to > >>> run in parallel on two engines. > >>> > >>> A -> B > >>> \- B' > >>> > >>> B will run after A and so may be scheduled on an idle engine and wait on > >>> A using a semaphore. B' sees B being executed and so enters the queue on > >>> the same engine as A. As B' did not inherit the semaphore-chain from B, > >>> it may have higher precedence than A and so preempts execution. However, > >>> B' then sits on a semaphore waiting for B, who is waiting for A, who is > >>> blocked by B. > >>> > >>> Ergo B' needs to inherit the scheduler properties from B (i.e. the > >>> semaphore chain) so that it is scheduled with the same priority as B and > >>> will not be executed ahead of Bs dependencies. > >>> > >>> Furthermore, to prevent the priorities changing via the expose fence on > >>> B', we need to couple in the dependencies for PI. This requires us to > >>> relax our sanity-checks that dependencies are strictly in order. > >> > >> Good catch, this needed some deep thinking! And it looks okay, even > >> though ideally we would be able to fix it not to signal the submit fence > >> until semaphore was completed. But for that I think we would need to > >> emit a request while emitting a request, so that the semaphore wait > >> would be in its own. > > > > At a push we could add an MI_USER_INTERRUPT after the initial breadcrumb > > and couple the submit fence into that. That would be virtually > > equivalent to emitting a separate request for semaphores. Something to > > ponder over. > > Hm, if not too difficult it would definitely be much preferable since > relying on controlling preemption decisions feels a bit fragile/hackish. > > Simply moving __notify_execute_cb from __i915_request_submit to > intel_engine_breadcrumbs_irq, under a __i915_request_has_started check, > could do it? 95% of the way, yes. -Chris _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
