linux-kernel - Re: [RFC] perf: need to expose sched_clock to correlate user samples with kernel samples

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Date:	Tue, 02 Apr 2013 17:05:52 +0100
From:	Pawel Moll <pawel.moll@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	John Stultz <john.stultz@...aro.org>,
	David Ahern <dsahern@...il.com>,
	Stephane Eranian <eranian@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Anton Blanchard <anton@...ba.org>,
	Will Deacon <Will.Deacon@....com>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Pekka Enberg <penberg@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Robert Richter <robert.richter@....com>
Subject: Re: [RFC] perf: need to expose sched_clock to correlate user
 samples with kernel samples

On Tue, 2013-04-02 at 08:54 +0100, Peter Zijlstra wrote:
> On Mon, 2013-04-01 at 11:29 -0700, John Stultz wrote:
> > I'm still not sold on the CLOCK_PERF posix clock. The semantics are 
> > still too hand-wavy and implementation specific.
> 
> How about we define the semantics as: match whatever comes out of perf
> (and preferably ftrace by default) stuff?

My thought exactly. Maybe if we defined it as "CLOCK_TRACE" and had
equivalent "trace_clock()" function used by both perf (instead of
perf_clock()) and ftrace the semantics would became clearer? This clock
could be then described as "source of timestamps used by Linux trace
infrastructure, in particular by ftrace and perf".

Paweł


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