Re: [PATCH] Perf: Correct Assumptions about Sample Timestamps inPasses

[David Ahern]

On 12/26/13, 8:30 AM, Frederic Weisbecker wrote:
> On Thu, Dec 26, 2013 at 10:24:03AM -0500, David Ahern wrote:
> > On 12/26/13, 10:14 AM, Frederic Weisbecker wrote:
> > > > I was carrying that patch while working on perf-kvm-stat-live last
> > > > Fall. It does not solve the problem for live commands, so ended up
> > > > dropping it and going with local (to the command) hacks. I still
> > > > think for live commands getting a perf_clock timestamp at the start
> > > > of a round and using that as the flush time will work best.

For perf-kvm-stat-live using perf_clock value at the start of the round 
as the flush time works beautifully:

https://github.com/dsahern/linux/commit/ba8b7b63d5dbdc95aedbbafa670c2232e0cc07a2

Never once failed with "Warning: Timestamp below last timeslice flush" 
error.

David

> > > Ok, but how would you fetch this perf clock timestamp, with an explicit read?
> >
> > One option is exporting perf_clock to userspace.
> >
> > Preferably a built-in option, https://lkml.org/lkml/2013/12/10/781,
> > but I can go the module route if I have to:
> > https://github.com/dsahern/linux/blob/perf-full-monty/README.ahern
>
> I see, that's one of the very verbose threads I've seen lately ;)


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