Quoting Tvrtko Ursulin (2019-04-09 16:38:37) > > On 09/04/2019 16:29, Chris Wilson wrote: > > Consider two tasks that are running in parallel on a pair of engines > > (vcs0, vcs1), but then must complete on a shared engine (rcs0). To > > maximise throughput, we want to run the first ready task on rcs0 (i.e. > > the first task that completes on either of vcs0 or vcs1). When using > > semaphores, however, we will instead queue onto rcs in submission order. > > > > To resolve this incorrect ordering, we want to re-evaluate the priority > > queue when each of the request is ready. Normally this happens because > > we only insert into the priority queue requests that are ready, but with > > semaphores we are inserting ahead of their readiness and to compensate > > we penalize those tasks with reduced priority (so that tasks that do not > > need to busywait should naturally be run first). However, given a series > > of tasks that each use semaphores, the queue degrades into submission > > fifo rather than readiness fifo, and so to counter this we give a small > > boost to semaphore users as their dependent tasks are completed (and so > > we no longer require any busywait prior to running the user task as they > > are then ready themselves). > > > > v2: Fixup irqsave for schedule_lock (Tvrtko) > > > > Testcase: igt/gem_exec_schedule/semaphore-codependency > > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx> > > Cc: Dmitry Rogozhkin <dmitry.v.rogozhkin@xxxxxxxxx> > > Cc: Dmitry Ermilov <dmitry.ermilov@xxxxxxxxx> > > --- [snip] > Looks fine to me. Provisional r-b: > > Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx> > > But let's wait for a media benchmarking run to see if you have nailed > the regression. Aye, but we need something like this regardless as introducing a trivial dos is not good behaviour either. Hopefully, this will evolve into something a lot more elegant. For now, it is just another lesson learnt. -Chris _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
