linux-kernel - [PATCH 2/4] perf annotate: Avoid division by zero when calculating percent

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Date:   Mon, 20 Mar 2017 11:56:55 +0900
From:   Taeung Song <treeze.taeung@...il.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Wang Nan <wangnan0@...wei.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Taeung Song <treeze.taeung@...il.com>,
        Jiri Olsa <jolsa@...hat.com>
Subject: [PATCH 2/4] perf annotate: Avoid division by zero when calculating percent

Currently perf-annotate with --print-line can print
-nan(0x8000000000000) because of division by zero
when calculating percent.

So if a sum of samples is zero, skip calculating percent.

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)

...

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)

...

Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Jiri Olsa <jolsa@...hat.com>
Signed-off-by: Taeung Song <treeze.taeung@...il.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 fc91c6b..9bb43cd 100644
--- a/tools/perf/util/annotate.c
+++ b/tools/perf/util/annotate.c
@@ -1665,11 +1665,15 @@ 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)
-- 
2.7.4