On 18/07/2017 16:19, Chris Wilson wrote:
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?
Hm it should be a plain spin_lock and a _bh variant on the external API.
But the purpose is to allow atomic sampling of accumulated busy time
plus the current engine status.
+ 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.
You mean both store in ktime_t and don't fetch the wall time but
monotonic? Do you say this because perf pmu perhaps needs monotonic or
for some other reason?
What is the cost of a ktime nowadays?
I don't see it in the profiles, so not much I think.
Regards,
Tvrtko
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