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Date: Sun, 31 Mar 2013 10:23:49 -0600
From: David Ahern <dsahern@gmail.com>
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To: Pawel Moll <pawel.moll@arm.com>, Stephane Eranian <eranian@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        John Stultz <john.stultz@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>
CC: LKML <linux-kernel@vger.kernel.org>, "mingo@elte.hu" <mingo@elte.hu>,
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        Will Deacon <Will.Deacon@arm.com>,
        "ak@linux.intel.com" <ak@linux.intel.com>,
        Pekka Enberg <penberg@gmail.com>, Steven Rostedt <rostedt@goodmis.org>,
        Robert Richter <robert.richter@amd.com>
Subject: Re: [RFC] perf: need to expose sched_clock to correlate user samples
 with kernel samples
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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