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Subject[tip:perf/core] perf annotate: Fix a bug of division by zero when calculating percent
Commit-ID:  2e933b1274dc89cd1629f6c7fd9bf952248d84c2
Gitweb: http://git.kernel.org/tip/2e933b1274dc89cd1629f6c7fd9bf952248d84c2
Author: Taeung Song <treeze.taeung@gmail.com>
AuthorDate: Mon, 27 Mar 2017 16:10:37 +0900
Committer: Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Mon, 27 Mar 2017 15:04:56 -0300

perf annotate: Fix a bug of division by zero when calculating percent

Currently perf-annotate with --print-line can print
-nan(0x8000000000000) because of division by zero when calculating
percent. The division by zero happens when a sum of samples is zero in
symbol__get_source_line(), so fix it.

For example:

After running 'perf record' like below,

$ perf record -e "{cycles,page-faults,branch-misses}" ./a.out

Before:

$ perf annotate --stdio -l

Sorted summary for file /home/taeung/workspace/a.out
----------------------------------------------

32.89 -nan 7.04 a.c:38
25.14 -nan 0.00 a.c:34
16.26 -nan 56.34 a.c:31
15.88 -nan 1.41 a.c:37
5.67 -nan 0.00 a.c:39
1.13 -nan 35.21 a.c:26
0.95 -nan 0.00 a.c:44
0.57 -nan 0.00 a.c:32
Percent | Source code & Disassembly of a.out for cycles (529 samples)
-----------------------------------------------------------------------------------------
:
...

a.c:26 0.57 -nan 4.23 : 40081a: mov %edi,-0x24(%rbp)
a.c:26 0.00 -nan 9.86 : 40081d: mov %rsi,-0x30(%rbp)

...

However, if a sum of samples is zero (e.g. 'page-faults'),
skip calculating percent.

After:

$ perf annotate --stdio -l

Sorted summary for file /home/taeung/workspace/a.out
----------------------------------------------

32.89 0.00 7.04 a.c:38
25.14 0.00 0.00 a.c:34
16.26 0.00 56.34 a.c:31
15.88 0.00 1.41 a.c:37
5.67 0.00 0.00 a.c:39
1.13 0.00 35.21 a.c:26
0.95 0.00 0.00 a.c:44
0.57 0.00 0.00 a.c:32
Percent | Source code & Disassembly of old for cycles (529 samples)
-----------------------------------------------------------------------------------------
:
...

a.c:26 0.57 0.00 4.23 : 40081a: mov %edi,-0x24(%rbp)
a.c:26 0.00 0.00 9.86 : 40081d: mov %rsi,-0x30(%rbp)

...

Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1490598638-13947-3-git-send-email-treeze.taeung@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/util/annotate.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/annotate.c b/tools/perf/util/annotate.c
index 6dc9148..11af5f0 100644
--- a/tools/perf/util/annotate.c
+++ b/tools/perf/util/annotate.c
@@ -1671,11 +1671,15 @@ static int symbol__get_source_line(struct symbol *sym, struct map *map,
src_line->nr_pcnt = nr_pcnt;

for (k = 0; k < nr_pcnt; k++) {
+ double percent = 0.0;
+
h = annotation__histogram(notes, evidx + k);
- src_line->samples[k].percent = 100.0 * h->addr[i] / h->sum;
+ if (h->sum)
+ percent = 100.0 * h->addr[i] / h->sum;

- if (src_line->samples[k].percent > percent_max)
- percent_max = src_line->samples[k].percent;
+ if (percent > percent_max)
+ percent_max = percent;
+ src_line->samples[k].percent = percent;
}

if (percent_max <= 0.5)
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