linux-kernel - Re: [PATCH 05/33] perf record: Allow the user to disable time stamps

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Date:	Tue, 5 Aug 2014 08:08:56 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
	Andi Kleen <andi@...stfloor.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Stephane Eranian <eranian@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH 05/33] perf record: Allow the user to disable time stamps


* Arnaldo Carvalho de Melo <acme@...nel.org> wrote:

> From: Andi Kleen <ak@...ux.intel.com>
> 

This patch looks dangerous and misleading to me.

> Time stamps are always implicitely enabled for record currently.  The
> old --time/-T option is a nop.
> 
> Allow the user to disable timestamps by using --no-time
> 
> This can cause some minor misaccounting (by missing mmaps), but
> significantly lowers the size of perf.data

I'm not any big change in size:

 -rw------- 1 mingo mingo 384768 Aug  5 08:01 perf.data.timestamps
 -rw------- 1 mingo mingo 336952 Aug  5 08:00 perf.data.notimestamps

That's a ~14% reduction - it's certainly noticeable but not 
earth-shattering.

And what is called 'minor misaccounting' in the description is 
actually a potentially broken profile that people might rely on.

So the patch description misleads twice: by exaggerating the 
advantages and also by downplaying the disadvantages.

So either remove the --time option altogether, or fix its 
'misaccounting' so that the profile can be relied on.

Thanks,

	Ingo
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