Messages in this thread | | | Date | Wed, 01 Jan 2014 11:37:55 -0700 | From | David Ahern <> | Subject | Re: [PATCH] Perf: Correct Assumptions about Sample Timestamps in Passes |
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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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