Quoting Tvrtko Ursulin (2018-01-22 11:45:04)
>
> On 22/01/2018 10:00, Chris Wilson wrote:
> > 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.
>
> It would have the advantage that multiple engines could be queried
> (more) atomically. How about then:
>
> I915_CONTEXT_ENABLE_ENGINE_STATS:
> value = &{
> __u32 num_engines;
> __u32 pad;
>
> struct {
> __u8 class;
> __u8 instance;
> __u8 pad[6];
> } [num_engines];
> };
>
> I915_CONTEXT_GET_ENGINE_STATS:
> value = &{
> __u32 num_engines;
> __u32 pad;
>
> struct {
> __u8 class;
> __u8 instance;
> __u8 pad[6];
>
> __u64 busy;
> } [num_engines];
> };
Yes, that's what I had in mind. How does that work in practice? Does it
make userspace too clumsy?
-Chris
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