[Intel-gfx] [RFC 05/12] drm/i915: Track runtime spent in unreachable intel_contexts

[Chris Wilson]

Quoting Tvrtko Ursulin (2020-03-09 18:31:22)
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> As contexts are abandoned we want to remember how much GPU time they used
> (per class) so later we can used it for smarter purposes.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_context.c       | 13 ++++++++++++-
>  drivers/gpu/drm/i915/gem/i915_gem_context_types.h |  5 +++++
>  2 files changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> index abc3a3e2fcf1..5f6861a36655 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> @@ -257,7 +257,19 @@ static void free_engines_rcu(struct rcu_head *rcu)
>  {
>         struct i915_gem_engines *engines =
>                 container_of(rcu, struct i915_gem_engines, rcu);
> +       struct i915_gem_context *ctx = engines->ctx;
> +       struct i915_gem_engines_iter it;
> +       struct intel_context *ce;
> +
> +       /* Transfer accumulated runtime to the parent GEM context. */
> +       for_each_gem_engine(ce, engines, it) {
> +               unsigned int class = ce->engine->uabi_class;
>  
> +               GEM_BUG_ON(class >= ARRAY_SIZE(ctx->past_runtime));
> +               atomic64_add(ce->runtime.total, &ctx->past_runtime[class]);
> +       }

-> give this its own routine.

> +
> +       i915_gem_context_put(ctx);
>         i915_sw_fence_fini(&engines->fence);
>         free_engines(engines);
>  }
> @@ -540,7 +552,6 @@ static int engines_notify(struct i915_sw_fence *fence,
>                         list_del(&engines->link);
>                         spin_unlock_irqrestore(&ctx->stale.lock, flags);
>                 }
> -               i915_gem_context_put(engines->ctx);

Or accumulate here? Here we know the engines are idle and released,
albeit there is the delay in accumulating after the swap. I'm not going
to worry about that, live replacement of engines I don't expect anyone
to notice the busy stats being off for a bit. Worst case is that they
see a sudden jump; but typical practice will be to setup engines up
before they being activity. We only have to worry about is if the
transient misleading stats can be exploited.
-Chris