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Date: Mon, 18 Aug 2014 13:31:47 +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 Sat, Aug 16, 2014 at 11:26:31AM +0900, Namhyung Kim wrote:
SNIP
> >
> > hum, where is it callee/caller mixed? with following example:
> >
> > ---
> > void c(void)
> > {
> > }
> >
> > void b(void)
> > {
> > c();
> > }
> >
> > void a(void)
> > {
> > b();
> > }
> >
> > int main(void)
> > {
> > while(1) {
> > a();
> > b();
> > c();
> > }
> > }
> > ---
> >
> > for 'c' the current code will display:
> >
> > - 43.74% 43.74% t t [.] c ▒
> > - __libc_start_main ▒
> > - 86.33% main ▒
> > 67.08% c ▒
> > - 32.91% a ▒
> > 99.44% c ▒
> > - 0.56% b ▒
> > c ▒
> > 13.67% c ▒
> >
> > and with this patch:
> >
> > - 43.74% 43.74% t t [.] c ▒
> > c ▒
> >
> >
> > The 'c' callchain is still in caller order. IMO we should
> > keep whole callchain here.
>
> The problem is not in pure self entry (that has self overhead = children
> overhead) and pure cumulative entry (self overhead = 0). It's in mixed
> entries, please see last two examples in the description 0/3.
right, but it still affects pure entries as well
anyway, let's see the mixed entry
for 'a' the current code will display:
- 31.97% 17.16% t t [.] a ▒
- __libc_start_main ◆
81.08% a ▒
- 18.92% main ▒
a ▒
- a ▒
85.05% c ▒
- 14.91% b ▒
100.00% c ▒
and with this patch:
- 31.97% 17.16% t t [.] a ▒
- a ▒
85.05% c ▒
- 14.91% b ▒
100.00% c ▒
so we'll miss the 'self' callchain of 'a' symbol
if we want to avoid the confusion about 2 different callchains, how
about marking them with 'self' and 'children' tags, instead of removing
one of them, like:
for 'a' the current code will display:
- 31.97% 17.16% t t [.] a ▒
- [self]
__libc_start_main ◆
81.08% a ▒
- 18.92% main ▒
a ▒
- [children]
a ▒
85.05% c ▒
- 14.91% b ▒
100.00% c ▒
jirka
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