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

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Date:	Tue, 25 Mar 2014 15:34:52 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	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

Stephane Eranian <eranian@...gle.com> writes:
>>
> But getting the mmaps at the right moment is crucial for some apps
> especially if address space is recycled otherwise symbolization
> may be incorrect.

Yes that is why it is only an option and not default.
You need to know what you're doing.

BTW I think the recycle case is not very likely on non JIT.

>> 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?

When I measure a long running process and I know it doesn't
fork/dlopen/jit. Using --initial-delay also helps to skip
the startup phase or attaching later.

I believe it's actually a good choice for most non
forky workloads. But yes it cannot be made default.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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