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

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Message-ID: <1364889256.16858.1.camel@laptop>
Date:	Tue, 02 Apr 2013 09:54:16 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	John Stultz <john.stultz@...aro.org>
Cc:	David Ahern <dsahern@...il.com>, Pawel Moll <pawel.moll@....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 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?

Since that stuff is already exposed to userspace, doesn't it make sense
to have a user accessible time source that generates the same time-line
so that people can create logs that can be properly interleaved?

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