Re: [PATCH 11/15] drm/i915/execlists: Cancel banned contexts on schedule-out

[Chris Wilson <chris@chris-wilson.co.uk>]

Quoting Chris Wilson (2019-10-14 13:34:35)
> Quoting Tvrtko Ursulin (2019-10-14 13:25:58)
> > 
> > On 14/10/2019 13:06, Chris Wilson wrote:
> > > Quoting Tvrtko Ursulin (2019-10-14 13:00:01)
> > >>
> > >> On 14/10/2019 10:07, Chris Wilson wrote:
> > >>> +static void cancel_active(struct i915_request *rq,
> > >>> +                       struct intel_engine_cs *engine)
> > >>> +{
> > >>> +     struct intel_context * const ce = rq->hw_context;
> > >>> +
> > >>> +     /*
> > >>> +      * The executing context has been cancelled. Fixup the context so that
> > >>> +      * it will be marked as incomplete [-EIO] upon resubmission and not
> > 
> > (read below first)
> > 
> > ... and not misleadingly say "Fixup the context so that it will be 
> > marked as incomplete" because there is nothing in this function which 
> > does that. It mostly happens by the virtual of context already being 
> > marked as banned somewhere else. This comment should just explain the 
> > decision to rewind the ring->head for more determinism. It can still 
> > mention canceling of user payload and -EIO. Just needs to be clear of 
> > the single extra thing achieved here by the head rewind and context edit.
> 
> I thought I was clear: "upon resubmission". So use a more active voice to
> reduce ambiguity, gotcha.

        /*
         * The executing context has been cancelled. We want to prevent
         * further execution along this context and propagate the error on
         * to anything depending on its results.
         *
         * In __i915_request_submit(), we apply the -EIO and remove the
         * requests payload for any banned requests. But first, we must
         * rewind the context back to the start of the incomplete request so
         * that we don't jump back into the middle of the batch.
         *
         * We preserve the breadcrumbs and semaphores of the incomplete
         * requests so that inter-timeline dependencies (i.e other timelines)
         * remain correctly ordered.
         */

-Chris
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