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

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Date:   Tue, 21 Mar 2017 07:11:13 +0900
From:   Taeung Song <treeze.taeung@...il.com>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
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>,
        Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH 2/4] perf annotate: Avoid division by zero when
 calculating percent

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@...et ~]# 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@...et ~]# perf annotate --stdio -l 2> /dev/null  | grep -i nan
> [root@...et ~]#
>
> 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@...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