[Intel-gfx] [RFC 3/8] drm/i915: Track per-context engine busyness

[Chris Wilson]

Quoting Tvrtko Ursulin (2020-01-10 13:30:44)
>  #endif /* __INTEL_CONTEXT_TYPES__ */
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> index 825c94e7ca0b..9a346c060469 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> @@ -1543,8 +1543,20 @@ int intel_enable_engine_stats(struct intel_engine_cs *engine)
>  
>                 engine->stats.enabled_at = ktime_get();
>  
> -               /* XXX submission method oblivious? */
> -               for (port = execlists->active; (rq = *port); port++)
> +               /*
> +                * Mark currently running context as active.
> +                * XXX submission method oblivious?
> +                */
> +
> +               rq = NULL;
> +               port = execlists->active;

execlists->active is never NULL (it always points at one of the arrays).
*execlists->active may be NULL.

> +               if (port)
> +                       rq = *port;
> +               if (rq)
> +                       __intel_context_stats_start(&rq->context->stats,
> +                                                   engine->stats.enabled_at);
> +
> +               for (; (rq = *port); port++)
>                         engine->stats.active++;
>  
> @@ -2250,6 +2277,7 @@ static void process_csb(struct intel_engine_cs *engine)
>         rmb();
>  
>         do {
> +               struct i915_request *rq;
>                 bool promote;
>  
>                 if (++head == num_entries)
> @@ -2305,7 +2333,11 @@ static void process_csb(struct intel_engine_cs *engine)
>  
>                         WRITE_ONCE(execlists->pending[0], NULL);
>                 } else {
> -                       GEM_BUG_ON(!*execlists->active);
> +                       rq = *execlists->active++;
> +                       GEM_BUG_ON(!rq);
> +
> +                       GEM_BUG_ON(execlists->active - execlists->inflight >
> +                                  execlists_num_ports(execlists));
>  
>                         /* port0 completed, advanced to port1 */
>                         trace_ports(execlists, "completed", execlists->active);
> @@ -2316,13 +2348,15 @@ static void process_csb(struct intel_engine_cs *engine)
>                          * coherent (visible from the CPU) before the
>                          * user interrupt and CSB is processed.
>                          */
> -                       GEM_BUG_ON(!i915_request_completed(*execlists->active) &&
> +                       GEM_BUG_ON(!i915_request_completed(rq) &&
>                                    !reset_in_progress(execlists));
> -                       execlists_schedule_out(*execlists->active++);
>  
> -                       GEM_BUG_ON(execlists->active - execlists->inflight >
> -                                  execlists_num_ports(execlists));
> +                       execlists_schedule_out(rq);
>                 }
> +
> +               rq = *execlists->active;
> +               if (rq)
> +                       intel_context_stats_start(&rq->context->stats);
>         } while (head != tail);

Actually, we can do this after processing the entire event buf.

if (execlists_active(execlists))
	intel_context_stats_start((*execlists->active)->context->stats);

Once we apply the fix in
https://patchwork.freedesktop.org/patch/347934/?series=71809&rev=1

We can in fact do this as a part of set_timeslice() which means we have
all the time-related updates in the same spot.
-Chris