linux-kernel - Re: [PATCH 13/16] perf callchain: Switch default to 'graph,0.5,caller'

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Message-ID: <20151021163506.GC19764@lerouge>
Date:	Wed, 21 Oct 2015 18:35:07 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
	Chandler Carruth <chandlerc@...il.com>,
	Brendan Gregg <brendan.d.gregg@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Borislav Petkov <bp@...e.de>, David Ahern <dsahern@...il.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Stephane Eranian <eranian@...gle.com>,
	Wang Nan <wangnan0@...wei.com>
Subject: Re: [PATCH 13/16] perf callchain: Switch default to
 'graph,0.5,caller'

On Wed, Oct 21, 2015 at 05:09:08PM +0900, Namhyung Kim wrote:
> On Tue, Oct 20, 2015 at 07:21:16PM +0200, Frederic Weisbecker wrote:
> > Well, I would prefer to hear from regular users than random twitter followers.
> > I could be wrong so lets ask some users first.
> 
> Just a question.  Do you often use --children and/or '--g caller' options?

I must confess I haven't used perf much for some time now. So I never
really used --children but I'm fairly convinced it's a very useful option.

> 
> I guess that for most kernel developers, --children is not that useful
> as you said.

Not sure about that. It provides a good overview.

> But I think it can be useful for many userspace
> developers and with '-g caller' it can be even more useful. :)
> 
> When '-g caller' is used, the callchains shown in a (self) entry are
> less important IMHO.  However callchains in entries generated by
> --children will show which functions are called by the entry (since
> it's reversed!) and will be more important.

Right and in fact the ever growing adoption of perf by userland developers
makes we start to understand why people are interested in caller based
callchains. Callee-based zoom into low level details that many people are not
interested in.

I think that if people could filter the callchain to only keep the part
concerning their binary, callee may suddenly become interesting for them.
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