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

From: David Ahern
Date: Wed Jan 01 2014 - 13:38:41 EST

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:

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


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,,
but I can go the module route if I have to:

I see, that's one of the very verbose threads I've seen lately ;)

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