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

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Message-ID: <52B84C49.70001@gmail.com>
Date:	Mon, 23 Dec 2013 09:44:25 -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 12/23/13, 8:10 AM, Frederic Weisbecker wrote:
> On Fri, Dec 20, 2013 at 10:09:53AM -0700, David Ahern wrote:
>> On 12/20/13, 5:27 AM, Joseph Schuchart wrote:
>>> I know this comes late, but: As far as I can see, your change does not
>>> preserve the logic of the code I suggested. The idea was to first gather
>>> all the maximum timestamps of all cpus (that is, the last timestamp seen
>>> on each cpu) and then determine the minimum of these maxima. These are
>>> two distinct steps that I think cannot be combined in one update. Your
>>
>>   A number of people have reported similar problems -- timestamps
>> below last flush time. This approach would solve that problem for
>> data processed from files, so it would be a good improvement.
>
> Could it be near what you're looking for?
>
> https://lkml.org/lkml/2012/2/18/53
>

Forgot about that patch. It is similar to what Joseph wants for 
analyzing a file.

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.

David
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