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

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Date:	Thu, 04 Apr 2013 17:33:22 +0100
From:	Pawel Moll <pawel.moll@....com>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	John Stultz <john.stultz@...aro.org>,
	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 Thu, 2013-04-04 at 08:37 +0100, Richard Cochran 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.

Sure it can - I've tested it. It's just a bit cumbersome in my opinion
(there is nothing else perf-related in /dev). I can agree to disagree if
you think otherwise :-)

> > 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.

By all means - and even more generic way than it is now (why character
devices not any other file?). I'll give it a try.

Paweł



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