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SubjectRe: [PATCH 2/4] perf annotate: Avoid division by zero when calculating percent
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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@kernel.org>
>>> Cc: Jiri Olsa <jolsa@redhat.com>
>>> Signed-off-by: Taeung Song <treeze.taeung@gmail.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

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