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

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Date:	Wed, 18 Nov 2015 17:02:41 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Jiri Olsa <jolsa@...hat.com>
CC:	Jiri Olsa <jolsa@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	David Ahern <dsahern@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Milian Wolff <milian.wolff@...b.com>,
	<linux-kernel@...r.kernel.org>, pi3orama <pi3orama@....com>,
	lizefan 00213767 <lizefan@...wei.com>
Subject: Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling
 taken at 'callq' instruction



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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