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

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Message-ID: <20151020172114.GB29289@lerouge>
Date:	Tue, 20 Oct 2015 19:21:16 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:	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>,
	Namhyung Kim <namhyung@...nel.org>,
	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 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.


> > > Ingo, what do you think?
> 
> What about providing a hotkey, in the tui, to toggle caller/callee
> views, and another hotkey to save that in ~/.perfconfig so that becomes
> the new default?

That means rebuilding the whole tree, it might be costly and events need to
be processed again.

> 
> In the --stdio mode we need to add a warning in the first lines,
> something like:
> 
> # This is caller (or callee) based, please use --callchain ... to change it
> 
> One way or the other people will disagree, so making it easy to switch
> to the preferred way would be nice to have?

Agreed.

Thanks!
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