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

From: Namhyung Kim <namhyung@kernel.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
	Chandler Carruth <chandlerc@gmail.com>,
	Brendan Gregg <brendan.d.gregg@gmail.com>,
	Ingo Molnar <mingo@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Borislav Petkov <bp@suse.de>, David Ahern <dsahern@gmail.com>,
	Jiri Olsa <jolsa@redhat.com>,
	Stephane Eranian <eranian@google.com>,
	Wang Nan <wangnan0@huawei.com>
Subject: Re: [PATCH 13/16] perf callchain: Switch default to 'graph,0.5,caller'
Date: Wed, 21 Oct 2015 17:09:08 +0900	[thread overview]
Message-ID: <20151021080908.GI628@sejong> (raw)
In-Reply-To: <20151020172114.GB29289@lerouge>

Hi Frederic,

On Tue, Oct 20, 2015 at 07:21:16PM +0200, Frederic Weisbecker wrote:
> On Tue, Oct 20, 2015 at 10:06:51AM -0300, Arnaldo Carvalho de Melo wrote:
> > Em Tue, Oct 20, 2015 at 02:19:50PM +0200, Frederic Weisbecker escreveu:
> > > On Tue, Oct 20, 2015 at 09:00:34AM -0300, Arnaldo Carvalho de Melo wrote:
> > > > Em Mon, Oct 19, 2015 at 05:16:53PM -0700, Brendan Gregg escreveu:
> > > > So are you advocating different defaults, one for --stdio (callee),
> > > > another for --tui, --gtk (caller)?
> > 
> > > > This is all configurable via ~/.perfconfig :-\
> > 
> > > > Indeed, finding a default that is deemed adequate for most people is,
> > > > ho-hum, difficult 8-)
> >  
> > > Most uses I've seen on LKML by the past involved callee because people
> > > mostly look at the precise point where a performance issue is.
> > 
> > A good chunk of that was because that was the default?
> 
> I doubt it. When you need to find the culprit of a syscall of IRQ performance issue,
> you don't care much to see __libc_start_main() / main() on the top of your callchain.
> 
> >  
> > > IMHO changing that order is not a good idea. Unless many users complained
> > > about it.
> > 
> > Perhaps there are not that many users of callchains because the default
> > is not what they're used to see?
> > 
> > Motivation for the change came from a video from Chandler, that
> > resurfaced the callchain default issue, Chandler?
> > 
> > Anedoctally, he tweeted about it and people seemed to like it.
> 
> 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 guess that for most kernel developers, --children is not that useful
as you said.  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.

Thanks,
Namhyung