[Intel-gfx] [PATCH 14/40] drm/i915: Load balancing across a virtual engine

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-05-08 11:29:34)
> 
> On 08/05/2019 09:06, Chris Wilson wrote:
> > +static int live_virtual_engine(void *arg)
> > +{
> > +     struct drm_i915_private *i915 = arg;
> > +     struct intel_engine_cs *siblings[MAX_ENGINE_INSTANCE + 1];
> > +     struct intel_engine_cs *engine;
> > +     enum intel_engine_id id;
> > +     unsigned int class, inst;
> > +     int err = -ENODEV;
> > +
> > +     if (USES_GUC_SUBMISSION(i915))
> > +             return 0;
> > +
> > +     mutex_lock(&i915->drm.struct_mutex);
> > +
> > +     for_each_engine(engine, i915, id) {
> > +             err = nop_virtual_engine(i915, &engine, 1, 1, 0);
> > +             if (err) {
> > +                     pr_err("Failed to wrap engine %s: err=%d\n",
> > +                            engine->name, err);
> > +                     goto out_unlock;
> > +             }
> > +     }
> > +
> > +     for (class = 0; class <= MAX_ENGINE_CLASS; class++) {
> > +             int nsibling, n;
> > +
> > +             nsibling = 0;
> > +             for (inst = 0; inst <= MAX_ENGINE_INSTANCE; inst++) {
> > +                     if (!i915->engine_class[class][inst])
> > +                             break;
> 
> I previous review I said I think this should be continue instead of 
> break so vcs0 + vcs2 skus can also be tested.

Completely missed that, sorry.

> > +
> > +                     siblings[nsibling++] = i915->engine_class[class][inst];
> > +             }
> > +             if (nsibling < 2)
> > +                     continue;
> 
> And also that single engine VE could be tested just as well, unless I am 
> missing something.

There's no such thing as single engine VE. The current design requires
that this type of struct virtual_engine encompasses more than one engine
(failing that we break the single request scheduling, although might be
able to lift that with timeslicing but the early results were not
favourable); the single engine being a regular intel_context instance.
-Chris