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

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Message-ID: <51586315.7080006@gmail.com>
Date:	Sun, 31 Mar 2013 10:23:49 -0600
From:	David Ahern <dsahern@...il.com>
To:	Pawel Moll <pawel.moll@....com>,
	Stephane Eranian <eranian@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	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 3/14/13 1:57 PM, Pawel Moll wrote:
> Ok, how about the code below? I must say I have some doubts about the
> resolution, as there seem to be no generic way of figuring it out for
> the sched_clock (the arch/arm/kernel/sched_clock.c is actually
> calculating it, but than just prints it out and nothing more).
>
> And, to summarize, we went through 3 ideas:
>
> 1. ioctl() - http://article.gmane.org/gmane.linux.kernel/1433933
> 2. syscall - http://article.gmane.org/gmane.linux.kernel/1437057
> 3. POSIX clock - below
>
> John also suggested that maybe the perf could use CLOCK_MONOTONIC_RAW
> instead of local/sched_clock().

Any chance a decision can be reached in time for 3.10? Seems like the 
simplest option is the perf event based ioctl.

Converting/correlating perf_clock timestamps to time-of-day is a feature 
I have been trying to get into perf for over 2 years. This is a big 
piece needed for that goal -- along with the xtime tracepoints:
   https://lkml.org/lkml/2013/3/19/433

David

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