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Date:   Thu, 23 Nov 2017 09:55:37 +0100
From:   Milian Wolff <milian.wolff@...b.com>
To:     alexander.levin@...izon.com
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        David Ahern <dsahern@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>,
        Yao Jin <yao.jin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH AUTOSEL for 4.14 18/51] perf callchain: Compare symbol name for inlined frames when matching

On Wednesday, November 22, 2017 11:25:40 PM CET alexander.levin@...izon.com 
wrote:
> From: Milian Wolff <milian.wolff@...b.com>
> 
> [ Upstream commit 9856240ad3269f2fdab0b2fa4400ef8aab792061 ]

Hello Alexander,

this is the first time I encounter AUTOSEL. I just want to check: The patch 
below depends on others in a whole series that reworks the handling of inline 
frames. Why is only this one getting selected? I don't even think it can work 
stand-alone?

Thanks

> The fake symbols we create for inlined frames will represent different
> functions but can use the symbol start address. This leads to issues
> when different inline branches all lead to the same function.
> 
> Before:
> ~~~~~
> $ perf report -s sym -i perf.inlining.data --inline --stdio -g function
> ...
>              --38.86%--_start
>                        __libc_start_main
>                        main
> 
>                         --37.57%--std::norm<double> (inlined)
>                                   std::_Norm_helper<true>::_S_do_it<double>
> (inlined)
> 
>                                    --36.36%--std::abs<double> (inlined)
>                                              std::__complex_abs (inlined)
> 
>                                              
> --12.24%--std::linear_congruential_engine<unsigned long, 16807ul, 0ul,
> 2147483647ul>::operator() (inlined) std::__detail::__mod<unsigned long,
> 2147483647ul, 16807ul, 0ul> (inlined) std::__detail::_Mod<unsigned long,
> 2147483647ul, 16807ul, 0ul, true, true>::__calc (inlined) ~~~~~
> 
> Note that this backtrace representation is completely bogus.
> Complex abs does not call the linear congruential engine! It
> is just a side-effect of a longer inlined stack being appended
> to a shorter, different inlined stack, both of which originate
> in the same function (main).
> 
> This patch fixes the issue:
> 
> ~~~~~
> $ perf report -s sym -i perf.inlining.data --inline --stdio -g function
> ...
>              --38.86%--_start
>                        __libc_start_main
>                        main
> 
>                        |--35.59%--std::uniform_real_distribution<double>::op
>                        |erator()<std::linear_congruential_engine<unsigned
>                        |long, 16807ul, 0ul, 2147483647ul> > (inlined)                       
|
>                        |          std::uniform_real_distribution<double>::op
>                        |          erator()<std::linear_congruential_engine<u
>                        |          nsigned long, 16807ul, 0ul, 2147483647ul>
>                        |          > (inlined)                       |          
>                        |           --34.37%--std::__detail::_Adaptor<std::li
>                        |           near_congruential_engine<unsigned long,
>                        |           16807ul, 0ul, 2147483647ul>,
>                        |           double>::operator() (inlined)                       
|           
>                        |                     std::generate_canonical<double,
>                        |                     53ul,
>                        |                     std::linear_congruential_engin
>                        |                     e<unsigned long, 16807ul, 0ul,
>                        |                     2147483647ul> > (inlined)                       
|                     
>                        |                      --12.24%--std::linear_congruen
>                        |                      tial_engine<unsigned long,
>                        |                      16807ul, 0ul,
>                        |                      2147483647ul>::operator()
>                        |                      (inlined)                       
|                      
>                        |                                std::__detail::__mod
>                        |                                <unsigned long,
>                        |                                2147483647ul,
>                        |                                16807ul, 0ul>
>                        |                                (inlined)
>                        |                                std::__detail::_Mod<
>                        |                                unsigned long,
>                        |                                2147483647ul,
>                        |                                16807ul, 0ul, true,
>                        |                                true>::__calc
>                        |                                (inlined)
>                         --1.99%--std::norm<double> (inlined)
>                                   std::_Norm_helper<true>::_S_do_it<double>
> (inlined) std::abs<double> (inlined)
>                                   std::__complex_abs (inlined)
> ~~~~~
> 
> Signed-off-by: Milian Wolff <milian.wolff@...b.com>
> Reviewed-by: Jiri Olsa <jolsa@...hat.com>
> Reviewed-by: Namhyung Kim <namhyung@...nel.org>
> Cc: David Ahern <dsahern@...il.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
> Cc: Yao Jin <yao.jin@...ux.intel.com>
> Link: http://lkml.kernel.org/r/20171009203310.17362-10-milian.wolff@kdab.com
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> [ Fix up conflict with c1fbc0cf81f1 ("perf callchain: Compare dsos (as well)
> for CCKEY_FUNCTION"), remove unneeded hunk ] Signed-off-by: Arnaldo
> Carvalho de Melo <acme@...hat.com>
> 
> Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
> ---
>  tools/perf/util/callchain.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
> index 6031933d811c..3cc51e852cf0 100644
> --- a/tools/perf/util/callchain.c
> +++ b/tools/perf/util/callchain.c
> @@ -697,6 +697,14 @@ static enum match_result match_chain(struct
> callchain_cursor_node *node, }
> 
>  	if (cnode->ms.sym && sym && callchain_param.key == CCKEY_FUNCTION) {
> +		/*
> +		 * Compare inlined frames based on their symbol name because
> +		 * different inlined frames will have the same symbol start
> +		 */
> +		if (cnode->ms.sym->inlined || node->sym->inlined)
> +			return match_chain_strings(cnode->ms.sym->name,
> +						   node->sym->name);
> +
>  		left = cnode->ms.sym->start;
>  		right = sym->start;
>  		left_dso = cnode->ms.map->dso;


-- 
Milian Wolff | milian.wolff@...b.com | Senior Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt Experts
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