Re: [PATCH 2/2] tracing/function-graph-tracer: use the morelightweight local clock

[Ingo Molnar]

* Frederic Weisbecker <fweisbec@xxxxxxxxx> wrote:

> > There will be one problem though: function trace elapsed 
> > time measurements across idle. Those are not correctly 
> > measured by the local clock.
> 
> Oh, why? If I'm not wrong it uses sched_clock() which uses tsc 
> on x86. And this register always goes forward at the same 
> rate. Unless some Cpu decrease their frequency while beeing 
> idle for some time and then become unreliable?

TSC stops in idle on many CPUs.

	Ingo
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