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

[Wangnan (F)]

On 2015/10/21 16:09, Namhyung Kim wrote:
> 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?

For me, I always use --no-children. However, I think it is because
I have used to --no-children and no one teach me how to utilize the
additional information --children provided. In case when result
of --no-children hard to explain I use Brendan's flame graph tool.

Thank you.

> 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


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