linux-kernel - Re: [PATCH] tools, perf: Allow the user to disable time stamps

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Date:	Tue, 25 Mar 2014 23:15:05 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Andi Kleen <ak@...ux.intel.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH] tools, perf: Allow the user to disable time stamps

On Tue, Mar 25, 2014 at 10:01 PM, Andi Kleen <ak@...ux.intel.com> wrote:
>>
>> Timestamp are useful to order samples during reporting.
>> How do you do with it if you monitor multi-threaded (multi-cpu)
>> workloads. This is only good for single thread or single CPU
>> measurements. Or am I missing something?
>
> For a perf report order doesn't matter (except against mmaps)
> The CPUs are still separated of course
>
But getting the mmaps at the right moment is crucial for some apps
especially if address space is recycled otherwise symbolization
may be incorrect.

> You're right for some special analysis it matters, that is why
> it is only an option.
>
> But for the standard "only care about perf report and
> don't care about about program startup" case it's a nice saving.
>
How do you know in advance you won't need mmap ordering?
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