linux-kernel - Re: [PATCH 2/2] perf: Add a new sort order: SORT

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Message-ID: <20120308153933.GD7976@somewhere.redhat.com>
Date:	Thu, 8 Mar 2012 16:39:36 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Arun Sharma <asharma@...com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	Namhyung Kim <namhyung.kim@....com>,
	Tom Zanussi <tzanussi@...il.com>,
	linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 2/2] perf: Add a new sort order: SORT_INCLUSIVE

On Wed, Mar 07, 2012 at 02:41:19PM -0800, Arun Sharma wrote:
> Each entry that used to get added once to the histogram, now is added
> chain->nr times, each time with one less entry in the
> callchain.
> 
> This will result in a non-leaf function that appears in a lot of
> samples to get a histogram entry with lots of hits.
> 
> The user can then drill down into the callchains of functions that
> have high inclusive times.

I don't yet understand the point of this.

Imagine those three hists:

a -> b -> c
a -> b -> d
a-> e -> f

The fractal inverted mode (-G) will report this:

a--
  |
  ----- b
  |     |
  |     -----c
  |     |
  |     -----d
  |
  ----- e
        |
        -----f

The branch sorting is recursive so outstanding callers appear
in the first branches already.

So if your goal is to find important callers, I don't see why
the existing functionalities aren't enough.
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