Quoting Tvrtko Ursulin (2017-07-18 15:36:15)
> From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
>
> Track total time requests have been executing on the hardware.
>
> To make this cheap it is hidden behind a static branch with the
> intention that it is only enabled when there is a consumer
> listening. This means that in the default off case the total
> cost of the tracking is just a few no-op instructions on the
> fast paths.
> +static inline void intel_engine_context_in(struct intel_engine_cs *engine)
> +{
> + if (static_branch_unlikely(&i915_engine_stats_key)) {
> + unsigned long flags;
> +
> + spin_lock_irqsave(&engine->stats.lock, flags);
What's the purpose of this lock? RMW is ordered by virtue of the tasklet
(only one cpu can be doing the rmw at any time). Did I miss another
user?
> + if (engine->stats.ref++ == 0)
> + engine->stats.start = ktime_get_real_ns();
Use ktime_get_raw() and leave the conversion to ns to the caller.
What is the cost of a ktime nowadays?
How do you handle the currently active case when reporting? Imagine a
continuous stream of requests, hoping between contexts without a
break.
-Chris
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