linux-kernel - Re: [PATCH 22/27] perf tools: Enable --children option by default

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Message-ID: <20140729114548.GA27368@alap3.anarazel.de>
Date:	Tue, 29 Jul 2014 13:45:48 +0200
From:	Andres Freund <andres@...razel.de>
To:	Namhyung Kim <namhyung@...il.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andi Kleen <andi@...stfloor.org>, Arun Sharma <asharma@...com>,
	Rodrigo Campos <rodrigo@...g.com.ar>,
	Don Zickus <dzickus@...hat.com>
Subject: Re: [PATCH 22/27] perf tools: Enable --children option by default

Hi,

On 2014-07-29 15:52:46 +0900, Namhyung Kim wrote:
> On Mon, 28 Jul 2014 21:23:26 +0200, Andres Freund wrote:
> > On 2014-05-29 12:58:25 +0900, Namhyung Kim wrote:
> >> Now perf top and perf report will show children column by default if
> >> it has callchain information.
> >> 
> >> Requested-by: Ingo Molnar <mingo@...nel.org>
> >> Tested-by: Rodrigo Campos <rodrigo@...g.com.ar>
> >> Tested-by: Arun Sharma <asharma@...com>
> >> Acked-by: Jiri Olsa <jolsa@...hat.com>
> >> Cc: Frederic Weisbecker <fweisbec@...il.com>
> >> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> >
> > Stupid question: Why? This breaks user's usage pattern in a rather
> > significant way because the new output is pretty much entirely useless
> > in many cases, especially for userland programs. I think the new option
> > is great, but why is it suddenly the default?
> 
> Yes, I knew it'd annoy some existing users like you :)  But I hoped it'd
> be useful for new and (at least, some of) old users to see children/
> cumulative overheads by default.  If it lies under an option, it
> wouldn't have a chance to be used by normal users who simply run perf
> record and report most of time.

By that argument every new feature would need to be enabled by
default. Which normally isn't what happens.

> If you think it's entirely useless for you cases, you can set it to off
> using ~/.perfconfig file:
> 
>   [report]
>   children = false

Already done that ;).

The problem is still that I can't use --no-children on older systems, so
I can't write benchmarking scripts anymore that don't take depend on the
perf version...

I guess it's too late to argue effectively though :)

Greetings,

Andres Freund
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