Re: [PATCH 2/4] perf annotate: Avoid division by zero when calculating percent
From: Taeung Song
Date: Mon Mar 20 2017 - 18:20:43 EST
And,
I tested by perf-stat on the same situation as below.
$ perf stat -e "{cycles,page-faults,branch-misses}" ./old <input.txt
6623856
Performance counter stats for './old':
472,007,763 cycles (99.85%)
71 page-faults (99.85%)
220,073 branch-misses (99.85%)
0.170768608 seconds time elapsed
Many times, the number of samples 'page-faults' was 68 ~ 71.
In spite of it, how did the below 'h->sum' is zero..
util/annotate.c:1660~1661
1660 h = annotation__histogram(notes, evidx + k);
1661 src_line->samples[k].percent = 100.0 * h->addr[i] / h->sum;
This patch just add if statement 'if (h->sum)' to handle the case
that h->sum is zero. But now I wonder how h->sum could be zero..
I'll dig the problem to find the root cause of it, too !
Thanks,
Taeung
On 03/21/2017 07:11 AM, Taeung Song wrote:
Hi Arnaldo :)
Here the perf.data is,
https://www.dropbox.com/s/nr4nnv8g3cipluf/perf.data?dl=1&pl=1
I tested as below.
$ perf record -e "{cycles,page-faults,branch-misses}" ./old <input.txt
$ perf annotate --stdio -l -f 2> /dev/null | grep -i nan | head -3
29.04 -nan 1.52 old_pack_knapsack.c:34
28.27 -nan 0.00 old_pack_knapsack.c:38
16.37 -nan 0.00 old_pack_knapsack.c:37
Thanks,
Taeung
On 03/21/2017 03:15 AM, Arnaldo Carvalho de Melo wrote:
Em Mon, Mar 20, 2017 at 11:56:55AM +0900, Taeung Song escreveu:
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.
Tried to reproduce it here, couldn't, syswide record:
[root@jouet ~]# perf evlist -v
cycles: size: 112, { sample_period, sample_freq }: 4000, sample_type:
IP|TID|TIME|CPU|PERIOD, disabled: 1, inherit: 1, mmap: 1, comm: 1,
freq: 1, task: 1, sample_id_all: 1, exclude_guest: 1, mmap2: 1,
comm_exec: 1
[root@jouet ~]# perf annotate --stdio -l 2> /dev/null | grep -i nan
[root@jouet ~]#
Can you please send me a perf.data file with this problem? I have to go
thru the code to see how this can take place...
- Arnaldo
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@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Signed-off-by: Taeung Song <treeze.taeung@xxxxxxxxx>
---
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