Re: [RFC] perf: need to expose sched_clock to correlate usersamples with kernel samples

[Pawel Moll]

On Thu, 2013-03-14 at 15:34 +0000, Stephane Eranian wrote:
> > Well, the timestamps themselves are already exposed to userspace
> > through the ftrace and perf data logs. All people want is to add
> > secondary data stream in the same time-line.
> >
> I agree with Peter on this. The timestamps are already visible.
> All we need is the ability to generate them for another user-level
> level data stream.

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().

How about a final decision?

Regards

Pawel

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