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Date:   Wed, 10 May 2017 14:53:52 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Milian Wolff <milian.wolff@...b.com>
Cc:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        David Ahern <dsahern@...il.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Yao Jin <yao.jin@...ux.intel.com>, kernel-team@....com
Subject: Re: [PATCH v2] perf report: distinguish between inliners in the same
 function

Hi,

On Wed, May 03, 2017 at 11:35:36PM +0200, Milian Wolff wrote:
> When different functions get inlined into the same function, we
> want to show them individually in the reports. But when we group by
> function, we would aggregate all IPs and would only keep the first
> one in that function. E.g. for C++ code like the following:
> 
> ~~~~~
> #include <cmath>
> #include <random>
> #include <iostream>
> 
> using namespace std;
> 
> int main()
> {
>     uniform_real_distribution<double> uniform(-1E5, 1E5);
>     default_random_engine engine;
>     double s = 0;
>     for (int i = 0; i < 10000000; ++i) {
>         s += uniform(engine);
>     }
>     cout << "random sum: " << s << '\n';
>     return 0;
> }
> ~~~~~
> 
> Building it with `g++ -O2 -g` and recording some samples with
> `perf record --call-graph dwarf` yields for me:
> 
> ~~~~~
> $ perf report --stdio --inline
> # Overhead  Command    Shared Object      Symbol
> # ........  .........  .................  ................................
> #
>     99.40%    99.11%  a.out    a.out                [.] main
>             |
>              --99.11%--_start
>                        __libc_start_main
>                        main
> ...
> ~~~~~
> 
> Note how no inlined frames are actually shown, because the first
> sample in main points to an IP that does not correspond to any
> inlined frames.
> 
> With this patch applied, we instead get the following, much more
> meaningful, reports.
> 
> ~~~~~
> $ perf report --stdio --inline --no-children
> # Overhead  Command    Shared Object      Symbol
> # ........  .........  .................  ................................
> #
>     99.11%  a.out    a.out             [.] main
>             |
>             |--48.15%--main
>             |          std::__detail::_Adaptor<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul>, double>::operator() (inline)
>             |          std::uniform_real_distribution<double>::operator()<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul> > (inline)
>             |          std::uniform_real_distribution<double>::operator()<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul> > (inline)
>             |          main (inline)
>             |          __libc_start_main
>             |          _start
>             |
>             |--47.61%--main
>             |          std::__detail::__mod<unsigned long, 2147483647ul, 16807ul, 0ul> (inline)
>             |          std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul>::operator() (inline)
>             |          std::generate_canonical<double, 53ul, std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul> > (inline)
>             |          std::__detail::_Adaptor<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul>, double>::operator() (inline)
>             |          std::uniform_real_distribution<double>::operator()<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul> > (inline)
>             |          std::uniform_real_distribution<double>::operator()<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul> > (inline)
>             |          main (inline)
>             |          __libc_start_main
>             |          _start
>             |
>              --3.35%--main
>                        std::uniform_real_distribution<double>::operator()<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul> > (inline)
>                        main (inline)
>                        __libc_start_main
>                        _start
> ...
> 
> $ perf report --stdio --inline
> # Children      Self  Command  Shared Object        Symbol
> # ........  ........  .......  ...................  ........................................................
> #
>     99.40%    99.11%  a.out    a.out                [.] main
>             |
>              --99.11%--_start
>                        __libc_start_main
>                        |
>                        |--70.51%--main
>                        |          main (inline)
>                        |          std::uniform_real_distribution<double>::operator()<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul> > (inline)
>                        |          std::uniform_real_distribution<double>::operator()<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul> > (inline)
>                        |          std::__detail::_Adaptor<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul>, double>::operator() (inline)
>                        |
>                        |--25.25%--main
>                        |          main (inline)
>                        |          std::uniform_real_distribution<double>::operator()<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul> > (inline)
>                        |          std::uniform_real_distribution<double>::operator()<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul> > (inline)
>                        |          std::__detail::_Adaptor<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul>, double>::operator() (inline)
>                        |          std::generate_canonical<double, 53ul, std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul> > (inline)
>                        |          std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul>::operator() (inline)
>                        |          std::__detail::__mod<unsigned long, 2147483647ul, 16807ul, 0ul> (inline)
>                        |
>                         --3.35%--main
>                                   main (inline)
>                                   std::uniform_real_distribution<double>::operator()<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul> > (inline)
> ~~~~~
> 
> Note that the latter top-down call graphs require us to traverse the
> full inliner call chain when comparing for equality. Without it,
> we would potentially combine the three distinct branches again, since
> they share an equal first inline frame "main (inline)".
> 
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: David Ahern <dsahern@...il.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Yao Jin <yao.jin@...ux.intel.com>
> Signed-off-by: Milian Wolff <milian.wolff@...b.com>
> ---
> v2:
> - compare the full stack of inlined frames to distinguish different branches
>   in top-down call-stack views which start with the same inlined frame(s)
> 
>  tools/perf/util/callchain.c | 87 ++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 75 insertions(+), 12 deletions(-)
> 
> diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
> index 81fc29ac798f..9ab68682c6d0 100644
> --- a/tools/perf/util/callchain.c
> +++ b/tools/perf/util/callchain.c
> @@ -618,15 +618,9 @@ enum match_result {
>  	MATCH_GT,
>  };
>  
> -static enum match_result match_chain_srcline(struct callchain_cursor_node *node,
> -					     struct callchain_list *cnode)
> +static enum match_result match_chain_strings(const char *left,
> +					     const char *right)
>  {
> -	char *left = get_srcline(cnode->ms.map->dso,
> -				 map__rip_2objdump(cnode->ms.map, cnode->ip),
> -				 cnode->ms.sym, true, false);
> -	char *right = get_srcline(node->map->dso,
> -				  map__rip_2objdump(node->map, node->ip),
> -				  node->sym, true, false);
>  	enum match_result ret = MATCH_EQ;
>  	int cmp;
>  
> @@ -636,19 +630,82 @@ static enum match_result match_chain_srcline(struct callchain_cursor_node *node,
>  		cmp = 1;
>  	else if (left && !right)
>  		cmp = -1;
> -	else if (cnode->ip == node->ip)
> -		cmp = 0;
>  	else
> -		cmp = (cnode->ip < node->ip) ? -1 : 1;
> +		return MATCH_ERROR;
>  
>  	if (cmp != 0)
>  		ret = cmp < 0 ? MATCH_LT : MATCH_GT;
>  
> +	return ret;
> +}
> +
> +static enum match_result match_chain_srcline(struct callchain_cursor_node *node,
> +					     struct callchain_list *cnode)
> +{
> +	char *left = get_srcline(cnode->ms.map->dso,
> +				 map__rip_2objdump(cnode->ms.map, cnode->ip),
> +				 cnode->ms.sym, true, false);
> +	char *right = get_srcline(node->map->dso,
> +				  map__rip_2objdump(node->map, node->ip),
> +				  node->sym, true, false);
> +	enum match_result ret = match_chain_strings(left, right);

I think we need to check inlined srcline as well.  There might be a
case that two samples have different addresses (and from different
callchains) but happens to be mapped to a same srcline IMHO.


> +
>  	free_srcline(left);
>  	free_srcline(right);
>  	return ret;
>  }
>  
> +static enum match_result match_chain_inliner(struct callchain_cursor_node *node,
> +					     struct callchain_list *cnode)
> +{
> +	u64 left_ip = map__rip_2objdump(cnode->ms.map, cnode->ip);
> +	u64 right_ip = map__rip_2objdump(node->map, node->ip);
> +	struct inline_node *left_node = NULL;
> +	struct inline_node *right_node = NULL;
> +	struct inline_list *left_entry = NULL;
> +	struct inline_list *right_entry = NULL;
> +	struct inline_list *left_last_entry = NULL;
> +	struct inline_list *right_last_entry = NULL;
> +	enum match_result ret = MATCH_EQ;
> +
> +	left_node = dso__parse_addr_inlines(cnode->ms.map->dso, left_ip);
> +	if (!left_node)
> +		return MATCH_ERROR;
> +
> +	right_node = dso__parse_addr_inlines(node->map->dso, right_ip);
> +	if (!right_node) {
> +		inline_node__delete(left_node);
> +		return MATCH_ERROR;
> +	}
> +
> +	left_entry = list_first_entry(&left_node->val,
> +				      struct inline_list, list);
> +	left_last_entry = list_last_entry(&left_node->val,
> +					  struct inline_list, list);
> +	right_entry = list_first_entry(&right_node->val,
> +				       struct inline_list, list);
> +	right_last_entry = list_last_entry(&right_node->val,
> +					  struct inline_list, list);

What about keeping number of entries in a inline_node so that we can
check the numbers for faster comparison?


> +	while (ret == MATCH_EQ && (left_entry || right_entry)) {
> +		ret = match_chain_strings(left_entry ? left_entry->funcname : NULL,
> +					  right_entry ? right_entry->funcname : NULL);
> +
> +		if (left_entry && left_entry != left_last_entry)
> +			left_entry = list_next_entry(left_entry, list);
> +		else
> +			left_entry = NULL;
> +
> +		if (right_entry && right_entry != right_last_entry)
> +			right_entry = list_next_entry(right_entry, list);
> +		else
> +			right_entry = NULL;
> +	}
> +
> +	inline_node__delete(left_node);
> +	inline_node__delete(right_node);
> +	return ret;
> +}
> +
>  static enum match_result match_chain(struct callchain_cursor_node *node,
>  				     struct callchain_list *cnode)
>  {
> @@ -671,7 +728,13 @@ static enum match_result match_chain(struct callchain_cursor_node *node,
>  	}
>  
>  	if (left == right) {
> -		if (node->branch) {
> +		if (symbol_conf.inline_name && cnode->ip != node->ip) {
> +			enum match_result match = match_chain_inliner(node,
> +								      cnode);
> +
> +			if (match != MATCH_ERROR)
> +				return match;

I guess it'd be better just returning the match result.  Otherwise
MATCH_ERROR will be converted to MATCH_EQ..

Thanks,
Namhyung


> +		} else if (node->branch) {
>  			cnode->branch_count++;
>  
>  			if (node->branch_flags.predicted)
> -- 
> 2.12.2
> 

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