[Intel-gfx] [PATCH 2/6] drm/i915: Allow clients to query own per-engine busyness

[Chris Wilson]

Quoting Tvrtko Ursulin (2018-01-22 09:53:27)
> 
> On 19/01/2018 21:08, Chris Wilson wrote:
> > Quoting Tvrtko Ursulin (2018-01-19 13:45:24)
> >> +       case I915_CONTEXT_GET_ENGINE_BUSY:
> >> +               engine = intel_engine_lookup_user(i915, args->class,
> >> +                                                 args->instance);
> >> +               if (!engine) {
> >> +                       ret = -EINVAL;
> >> +                       break;
> >> +               }
> >> +
> >> +               ce = &ctx->engine[engine->id];
> >> +               if (!READ_ONCE(ce->stats.enabled)) {
> >> +                       ret = i915_mutex_lock_interruptible(dev);
> >> +                       if (!ret)
> >> +                               break;
> >> +
> >> +                       if (!ce->stats.enabled) {
> >> +                               ret = intel_enable_engine_stats(engine);
> > 
> > * Blink.
> > 
> > This caught me by surprise. (Other than struct_mutex) Not too offensive,
> > but surprising. At the very least call out to a function to handle the
> > request. Where did args->class, args->instance come from? You surely
> > didn't extend the ioctl struct just for that?
> 
> Haven't extended it no, just did this:
> 
> --- a/include/uapi/drm/i915_drm.h
> +++ b/include/uapi/drm/i915_drm.h
> @@ -1468,7 +1468,16 @@ struct drm_i915_gem_context_param {
>   #define   I915_CONTEXT_MAX_USER_PRIORITY      1023 /* inclusive */
>   #define   I915_CONTEXT_DEFAULT_PRIORITY               0
>   #define   I915_CONTEXT_MIN_USER_PRIORITY      -1023 /* inclusive */
> -       __u64 value;
> +#define I915_CONTEXT_GET_ENGINE_BUSY   0x7
> +       union {
> +               __u64 value;
> +               struct {
> +                       __u8 pad[6]; /* unused */
> +
> +                       __u8 class;
> +                       __u8 instance;
> +               };
> +       };
>   };

Not entirely happy about mixing in/out parameters. It's already
complicated by being either an out value or an out pointer.

Closer to the original idea for context_getparam would be to return the
array of engine values.
-Chris