linux-kernel - Re: [PATCH] Perf: Correct Assumptions about Sample Timestamps in Passes

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Message-ID: <52BC4A13.1090508@gmail.com>
Date:	Thu, 26 Dec 2013 10:24:03 -0500
From:	David Ahern <dsahern@...il.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Joseph Schuchart <joseph.schuchart@...dresden.de>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	thomas.ilsche@...dresden.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Perf: Correct Assumptions about Sample Timestamps in
 Passes

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.
>
> 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

David
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