[Intel-gfx] [RFC 08/12] drm/i915: Expose per-engine client busyness

[Chris Wilson]

Quoting Tvrtko Ursulin (2020-03-10 20:04:23)
> 
> On 10/03/2020 18:32, Chris Wilson wrote:
> > Quoting Tvrtko Ursulin (2020-03-09 18:31:25)
> >> +static ssize_t
> >> +show_client_busy(struct device *kdev, struct device_attribute *attr, char *buf)
> >> +{
> >> +       struct i915_engine_busy_attribute *i915_attr =
> >> +               container_of(attr, typeof(*i915_attr), attr);
> >> +       unsigned int class = i915_attr->engine_class;
> >> +       struct i915_drm_client *client = i915_attr->client;
> >> +       u64 total = atomic64_read(&client->past_runtime[class]);
> >> +       struct list_head *list = &client->ctx_list;
> >> +       struct i915_gem_context *ctx;
> >> +
> >> +       rcu_read_lock();
> >> +       list_for_each_entry_rcu(ctx, list, client_link) {
> >> +               total += atomic64_read(&ctx->past_runtime[class]);
> >> +               total += pphwsp_busy_add(ctx, class);
> >> +       }
> >> +       rcu_read_unlock();
> >> +
> >> +       total *= RUNTIME_INFO(i915_attr->i915)->cs_timestamp_period_ns;
> > 
> > Planning early retirement? In 600 years, they'll have forgotten how to
> > email ;)
> 
> Shruggety shrug. :) I am guessing you would prefer both internal 
> representations (sw and pphwsp runtimes) to be consistently in 
> nanoseconds? I thought why multiply at various places when once at the 
> readout time is enough.

It's fine. I was just double checking overflow, and then remembered the
end result is 64b nanoseconds.

Keep the internal representation convenient for accumulation, and the
conversion at the boundary.
 
> And I should mention again how I am not sure at the moment how to meld 
> the two stats into one more "perfect" output.

One of the things that crossed my mind was wondering if it was possible
to throw in a pulse before reading the stats (if active etc). Usual
dilemma with non-preemptible contexts, so probably not worth it as those
hogs will remain hogs.

And I worry about the disparity between sw busy and hw runtime.
-Chris