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

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Date:	Tue, 05 Feb 2013 20:19:55 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Stephane Eranian <eranian@...gle.com>,
	Pawel Moll <pawel.moll@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	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>,
	Robert Richter <robert.richter@....com>,
	tglx <tglx@...utronix.de>
Subject: Re: [RFC] perf: need to expose sched_clock to correlate user
 samples with kernel samples

On Tue, 2013-02-05 at 14:28 -0800, John Stultz wrote:
> I prefer the ioctl method, since its less likely to be re-purposed/misused.
> 
> Though I'd be most comfortable with finding some way for perf-timestamps 
> to be CLOCK_MONOTONIC based (or maybe CLOCK_MONOTONIC_RAW if it would be 
> easier), and just avoid all together adding another time domain that 
> doesn't really have clear definition (other then "what perf uses").

Perhaps add a new perf system call? Does everything need to go through
the one great mighty perf_ioctl aka sys_perf_event_open()? I mean, if
there's something that can be agnostic to an event, but still very much
related to perf, perhaps another perf syscall should be created.

If people are worried about adding a bunch of new perf syscalls, maybe
add a sys_perf_control() system call that works like an ioctl but
without a file descriptor. Something for things that don't require an
event attached to it, like to retrieve a time stamp counter that perf
uses, but done in a way that it could be used for other things perf
related that does not require an event.

-- Steve

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