Re: [RFC] perf: need to expose sched_clock to correlate user sampleswith kernel samples

[David Ahern]

On 4/3/13 8:00 AM, Stephane Eranian wrote:
> > What's the advantage of changing apps -- like the JIT compiler -- to emit
> > perf based timestamps versus having perf emit existing timestamps? ie.,
> > monotonic and realtime clocks already have vdso mappings for userspace with
> > well known performance characteristics. Why not have perf convert its
> > perf_clock timestamps into monotonic or realtime when dumping events?
> Can monotonic timestamps be obtained from NMI context in the kernel?

I don't understand the context of the question.

I am not suggesting perf_clock be changed. I am working on correlating 
existing perf_clock timestamps to clocks typically used by apps 
(REALTIME and time-of-day but also applies to MONOTONIC).

You are wanting the reverse -- have apps emit perf_clock timestamps. I 
was just wondering what is the advantage of this approach?

David

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