linux-kernel - Re: perf report fractal output issue

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Date:	Tue, 20 Oct 2009 23:53:14 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Anton Blanchard <anton@...ba.org>
Cc:	mingo@...e.hu, paulus@...ba.org, a.p.zijlstra@...llo.nl,
	linux-kernel@...r.kernel.org
Subject: Re: perf report fractal output issue

On Fri, Oct 16, 2009 at 10:41:26AM +1100, Anton Blanchard wrote:
> 
> Hi,
> 
> > > It looks like callchain__fprintf_graph() only prints the callchain if we
> > > have at least one rb entry at the top. In my case all the associated
> > > backtraces are identical so I assume we dont have to do any splitting.
> >
> > Hmm, could you please send me a perf.data where you can see that?
> > Does that only happen on powerpc?
> 
> I can replicate this on x86 by taking a perf.data and truncating it
> after the first sample+backtrace:
> 
> 
> # wget http://samba.org/~anton/perf_truncated.test
> 
> 
> # perf report -i perf_truncated.test -g fractal
> ...
>    100.00%     perf  [kernel]       [k] native_write_msr_safe
> 
> 
> # perf report -i perf_truncated.test -g flat
> ...
>    100.00%     perf  [kernel]       [k] native_write_msr_safe
>            100.00%
>                 native_write_msr_safe
>                 intel_pmu_enable_all
>                 hw_perf_enable
>                 perf_enable
>                 __perf_counter_enable
>                 smp_call_function_single
>                 task_oncpu_function_call
>                 perf_counter_enable
>                 perf_counter_for_each_child
>                 perf_ioctl
>                 vfs_ioctl
>                 do_vfs_ioctl
>                 sys_ioctl
>                 system_call_fastpath
>                 0x7f00c1857537


Thanks, I can reproduce it with your file.
Actually it was there from the beginning but we have missed it:
the root of the callchain is never printed :-s

Say you have:

hist_entry
    |
    --------- f1
              f2
              |
              -------- f3
              |        f4
              |
              ---------f5
                       f6

Actually you never see that, instead you have:

hist_entry
    |
    --------- f3
    |         f4
    |
    --------- f5
              f6

Thanks a lot for this report!
I'm currently fixing it.

I just hope the fix won't be too big for .32 ....

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