linux-kernel - Re: [PATCH 3/3] perf callchain: Prune misleading callchains for self entries

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Message-ID: <20140814141056.GA7630@krava.brq.redhat.com>
Date:	Thu, 14 Aug 2014 16:10:57 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arun Sharma <asharma@...com>,
	Rodrigo Campos <rodrigo@...g.com.ar>
Subject: Re: [PATCH 3/3] perf callchain: Prune misleading callchains for self
 entries

On Thu, Aug 14, 2014 at 03:01:40PM +0900, Namhyung Kim wrote:

SNIP

> However, with --children feature added, it now can show all callees of
> the entry.  For example, "start_kernel" entry now can display it calls
> rest_init and in turn cpu_idle and then cpuidle_idle_call (95.72%).
> 
>      6.14%     0.00%  swapper          [kernel.kallsyms]   [k] start_kernel
>                    |
>                     --- start_kernel
>                         rest_init
>                         cpu_idle
>                        |
>                        |--97.52%-- cpuidle_idle_call
>                        |          cpuidle_enter_tk
>                        |          |
>                        |          |--99.91%-- cpuidle_wrap_enter
>                        |          |          cpuidle_enter
>                        |          |          intel_idle
>                        |           --0.09%-- [...]
>                         --2.48%-- [...]
> 
> Note that start_kernel has no self overhead - meaning that it never
> get sampled by itself but constructs such a nice callgraph.  But,
> sadly, if an entry has self overhead, callchain will get confused with
> generated callchain (like above) and self callchains (which reversed
> order) like the eariler example.
> 
> To be consistent with other entries, I'd like to make it just to show
> a single entry - itself - like below since it doesn't have callees
> (children) at all.  But still use the whole callchain to construct
> children entries (like the start_kernel) as usual.
> 
>     40.53%    40.53%  swapper          [kernel.kallsyms]   [k] intel_idle
>                     |
>                     --- intel_idle

I understand the consistency point, but I think we'd loose
usefull info by cutting this off

I guess I can run 'report -g callee' to find out who called intel_idle
instead.. but I would not need to if the callchain stays here

jirka
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