From: Ingo Molnar <mingo@elte.hu>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] tracing/function-graph-tracer: use the more lightweight local clock
Date: Thu, 5 Mar 2009 12:38:28 +0100 [thread overview]
Message-ID: <20090305113828.GA9548@elte.hu> (raw)
In-Reply-To: <20090305112322.GH5359@nowhere>
* Frederic Weisbecker <fweisbec@gmail.com> 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
next prev parent reply other threads:[~2009-03-05 11:38 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-03-05 0:49 [PATCH 2/2] tracing/function-graph-tracer: use the more lightweight local clock Frederic Weisbecker
2009-03-05 1:19 ` Frederic Weisbecker
2009-03-05 7:30 ` Peter Zijlstra
2009-03-05 8:46 ` Frederic Weisbecker
2009-03-05 10:56 ` Ingo Molnar
2009-03-05 11:16 ` Frederic Weisbecker
2009-03-05 11:56 ` Ingo Molnar
2009-03-05 14:01 ` Frederic Weisbecker
2009-03-05 14:22 ` Ingo Molnar
2009-03-05 11:03 ` [tip:tracing/function-graph-tracer] " Frederic Weisbecker
2009-03-05 11:04 ` [PATCH 2/2] " Ingo Molnar
2009-03-05 11:23 ` Frederic Weisbecker
2009-03-05 11:38 ` Ingo Molnar [this message]
2009-03-05 11:18 ` [tip:tracing/function-graph-tracer] " Frederic Weisbecker
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