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SubjectRe: [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@redhat.com>
> Cc: David Ahern <dsahern@gmail.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Yao Jin <yao.jin@linux.intel.com>
> Signed-off-by: Milian Wolff <milian.wolff@kdab.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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