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

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Date:	Wed, 14 Nov 2012 18:30:16 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	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 Wed, 2012-11-14 at 14:26 -0800, John Stultz wrote:

> > There's also trace_clock_counter() which isn't even a clock :-)  It's
> > just a incremental atomic counter that goes up every time it's called.
> > This is the most synced clock, but is absolutely meaningless for
> > timestamps. It's just a way to show ordered events.
> 
> Oof. This is getting uglier. I'd really prefer not to expose all these 
> different internal clocks out userland. Especially via clock_gettime().

Actually, I would be happy to just expose them to modules. As things
like hwlat_detect could use them.

-- Steve


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