Re: [PATCH 2/4] perf annotate: Avoid division by zero when calculating percent
From: Arnaldo Carvalho de Melo
Date: Tue Mar 21 2017 - 10:14:17 EST
Em Tue, Mar 21, 2017 at 07:20:20AM +0900, Taeung Song escreveu:
> And,
> I tested by perf-stat on the same situation as below.
>
> $ perf stat -e "{cycles,page-faults,branch-misses}" ./old <input.txt
> 6623856
Please always try to spell out all the steps needed to get to some
result, for instance, in this case the info above, that you are asking
for three counters to be recorded at once probably has the key to
reproduce this, as I think that you may run your workload and sometimes
not get one page fault, leading tho that division by zero, but I have to
try to reproduce it now that I have this clue.
Thanks,
- Arnaldo
> 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