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

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Date:	Thu, 4 Apr 2013 09:37:00 +0200
From:	Richard Cochran <richardcochran@...il.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Pawel Moll <pawel.moll@....com>,
	Peter Zijlstra <peterz@...radead.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 Wed, Apr 03, 2013 at 10:50:57AM -0700, John Stultz wrote:
> 
> I get the reasoning around reusing the fd we already have, but is
> the possibility of a dynamic chardev pathname really a big concern?

I have been following this thread, and, not knowing very much about
perf, I would think that the userland can easily open a second file
(the dynamic posix clock chardev) in order to get these time stamps.

> Maybe can we extend the dynamic posix clock code to work on more
> then just the chardev? Although I worry about multiplexing too much
> functionality on the file.

I don't yet see a need for that, but if we do, then it should work in
a generic way, and not as a list of special cases, like we saw in the
patch.

Thanks,
Richard
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