lkml.org 
[lkml]   [2011]   [Sep]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 08/16] perf stat: Fix +- nan% in --no-aggr runs
Date
From: Jim Cromie <jim.cromie@gmail.com>

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>
---
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 a43c680..af0d65b 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);
}
--
1.6.2.5


\
 
 \ /
  Last update: 2011-09-30 00:53    [from the cache]
©2003-2011 Jasper Spaans