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

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Message-ID: <20170320181559.GD27647@kernel.org>
Date:   Mon, 20 Mar 2017 15:15:59 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Taeung Song <treeze.taeung@...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

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