Quoting Tvrtko Ursulin (2020-03-25 10:43:55) > > On 25/03/2020 10:13, Chris Wilson wrote: > > We set the priority hint on execlists to avoid executing the tasklet for > > when we know that there will be no change in execution order. However, > > as we set it from the virtual engine for all siblings, but only one > > physical engine may respond, we leave the hint set on the others > > stopping direct submission that could take place. > > > > If we do not set the hint, we may attempt direct submission even if we > > don't expect to submit. If we set the hint, we may not do any submission > > until the tasklet is run (and sometimes we may park the engine before > > that has had a chance). Ergo there's only a minor ill-effect on mixed > > virtual/physical engine workloads where we may try and fail to do direct > > submission more often than required. (Pure virtual / engine workloads > > will have redundant tasklet execution suppressed as normal.) > > > > Closes: https://gitlab.freedesktop.org/drm/intel/issues/1522 > > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx> > > --- > > drivers/gpu/drm/i915/gt/intel_lrc.c | 4 +--- > > 1 file changed, 1 insertion(+), 3 deletions(-) > > > > diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c > > index 210f60e14ef4..f88d3b95c4e1 100644 > > --- a/drivers/gpu/drm/i915/gt/intel_lrc.c > > +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c > > @@ -4985,10 +4985,8 @@ static void virtual_submission_tasklet(unsigned long data) > > submit_engine: > > GEM_BUG_ON(RB_EMPTY_NODE(&node->rb)); > > node->prio = prio; > > - if (first && prio > sibling->execlists.queue_priority_hint) { > > - sibling->execlists.queue_priority_hint = prio; > > + if (first && prio > sibling->execlists.queue_priority_hint) > > tasklet_hi_schedule(&sibling->execlists.tasklet); > > - } > > > > spin_unlock(&sibling->active.lock); > > } > > > > Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx> > > The queue_priority_hint scheme with virtual engine design is a bit > problematic, since we have no way to unwind. And it's spreading it's > tentacles all over the place. Oh well. Hear, hear. > Could we one day consider just peeking at the top of the tree(s) The problem is that we have a single attention bit (tasklet_schedule). So if we add a new virtual engine below the top of the tree, and we race with two engines pulling from the virtual trees, we need both engines to claim a virtual request or else we waste the tasklet and do not have a second wakeup queued. I don't think we can drop rechecking the virtual rbtree if we lose the race in the execlists tasklet. -Chris _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
