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| author | Jim Cromie <jim.cromie@gmail.com> | 2011-09-07 17:14:01 -0600 |
|---|---|---|
| committer | Arnaldo Carvalho de Melo <acme@redhat.com> | 2011-09-29 17:03:46 -0300 |
| commit | 19f4740255668ca297dcf9f02d80eb9bc87a1d66 (patch) | |
| tree | be6310424c3f7b0abc2f0e353a9304f5e6453878 /tools | |
| parent | 56f3bae70638b33477a6015fd362ccfe354fd3ee (diff) | |
| download | linux-19f4740255668ca297dcf9f02d80eb9bc87a1d66.tar.bz2 | |
perf stat: Fix +- nan% in --no-aggr runs
Without this patch, running:
$ sudo ./perf stat -r20 --no-aggr -a perl -e '$i++ for 1..100000'
I get computations like this:
CPU0 12.488247 task-clock # 1.224 CPUs utilized ( +- -nan% )
CPU1 12.488909 task-clock # 1.225 CPUs utilized ( +- -nan% )
CPU2 12.500221 task-clock # 1.226 CPUs utilized ( +- -nan% )
CPU3 12.481713 task-clock # 1.224 CPUs utilized ( +- -nan% )
but with patch, I get:
CPU0 8.233682 task-clock # 0.754 CPUs utilized ( +- 0.00% )
CPU1 8.226318 task-clock # 0.754 CPUs utilized ( +- 0.00% )
CPU2 8.210737 task-clock # 0.752 CPUs utilized ( +- 0.00% )
CPU3 8.201691 task-clock # 0.751 CPUs utilized ( +- 0.00% )
Note that without --no-aggr, I get non-0 statistics both before and after patch:
231.986022 task-clock # 4.030 CPUs utilized ( +- 0.97% )
212 context-switches # 0.001 M/sec ( +- 12.07% )
9 CPU-migrations # 0.000 M/sec ( +- 25.80% )
466 page-faults # 0.002 M/sec ( +- 3.23% )
174,318,593 cycles # 0.751 GHz ( +- 1.06% )
I couldnt see anything wrong in the caller, so fixed it in
stddev_stats(). ISTM that 0.00 is better than nan, since perf stat was
passed -A (--no-aggr) so no standard deviation should be expected, and
nan is suggestive of a deeper error.
When running with --no-aggr, perhaps we should suppress the statistics
printing entirely, or do so when they are 0.00.
Link: http://lkml.kernel.org/r/1315437244-3788-3-git-send-email-jim.cromie@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Diffstat (limited to 'tools')
| -rw-r--r-- | tools/perf/builtin-stat.c | 9 |
1 files changed, 7 insertions, 2 deletions
diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c index a43c68051078..af0d65b41416 100644 --- a/tools/perf/builtin-stat.c +++ b/tools/perf/builtin-stat.c @@ -254,8 +254,13 @@ static double avg_stats(struct stats *stats) */ static double stddev_stats(struct stats *stats) { - double variance = stats->M2 / (stats->n - 1); - double variance_mean = variance / stats->n; + double variance, variance_mean; + + if (!stats->n) + return 0.0; + + variance = stats->M2 / (stats->n - 1); + variance_mean = variance / stats->n; return sqrt(variance_mean); } |