Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling taken at 'callq' instruction

[Wangnan (F)]

On 2015/11/18 16:48, Jiri Olsa wrote:
> On Wed, Nov 18, 2015 at 03:20:36PM +0800, Wangnan (F) wrote:
>
> SNIP
>
> > Then use perf to trace it:
> >
> > # ./pref record  -g -F 9 --call-graph dwarf ./test_dwarf_unwind
> > # ./perf report  --no-children --stdio
> >       ...
> >       1.23%  test_dwarf_unwi  test_dwarf_unwind  [.] funcc
> >              |
> >              ---funcc
> >                 |
> >                 |--0.62%-- funcb
> >                 |          funca
> >                 |          main
> >                 |          __libc_start_main
> >                 |          _start
> >                 |
> >                  --0.62%-- 0   <-- I applied Jiri's patch in [1] so see this
> > 0,
> >                                    which indicates a broken call chain.
> can't see this case after multiple running your test,
> just the 'end-of-the-callchain' zeros
>
>      49.14%  test_dwarf_unwi  [vdso]             [.] __vdso_gettimeofday
>              |
>              ---__vdso_gettimeofday
>                 funcc
>                 funcb
>                 funca
>                 main
>                 __libc_start_main
>                 _start
>                 0
>
>      40.78%  test_dwarf_unwi  [vdso]             [.] 0x0000000000000987
>              |
>              ---0x7ffe28ab7987
>                 __vdso_gettimeofday
>                 funcc
>                 funcb
>                 funca
>                 main
>                 __libc_start_main
>                 _start
>                 0
>
>
> what kernel do you have?

My kernel is 4.3-rc4.

Please see my reply to Ingo. It is possible a problem related
to hardware and PEBS? Maybe on your system perf never capture
samples on 'callq'? I tested 'cycle' and 'cycle:p', can't get
such samples. Only 'cycles:pp' (the default event) have this
problem.

Thank you.

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