linux-kernel - Re: perf stat stddev reporting broken since "perf stat: Introduce read

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Date:	Tue, 19 Jan 2016 09:16:23 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Mel Gorman <mgorman@...hsingularity.net>
Cc:	Jiri Olsa <jolsa@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: perf stat stddev reporting broken since "perf stat: Introduce
 read_counters function"

On Tue, Jan 19, 2016 at 08:42:28AM +0100, Jiri Olsa wrote:

SNIP

> > 
> >  Performance counter stats for 'sleep 1' (5 runs):
> > 
> >           0.583178      task-clock (msec)         #    0.001 CPUs utilized
> >                  1      context-switches          #    0.002 M/sec
> >                  0      cpu-migrations            #    0.000 K/sec
> >                 67      page-faults               #    0.141 M/sec
> >          1,224,416      cycles                    #    2.585 GHz
> >    <not supported>      stalled-cycles-frontend
> >    <not supported>      stalled-cycles-backend
> >            892,568      instructions              #    0.68  insns per cycle
> >            184,975      branches                  #  390.554 M/sec
> >              8,512      branch-misses             #    4.57% of all branches
> > 
> >        1.000889249 seconds time elapsed                                          ( +-  0.01% )
> > 
> > I checked and current master in Linus' tree is also broken. Is this
> > change in documented perf stat behaviour intentional?
> 
> nope, not intentional.. I'll check on that, thanks for reporting

for some reason we initialized the stat every iteration,
(the call is also wrong because it's called only over the
first res_stats[0])

attached patch works for me, could you please test?
I'll run more tests and put it in my queue

thanks,
jirka


---
diff --git a/tools/perf/util/stat.c b/tools/perf/util/stat.c
index 2f901d15e063..2b58edccd56f 100644
--- a/tools/perf/util/stat.c
+++ b/tools/perf/util/stat.c
@@ -310,7 +310,6 @@ int perf_stat_process_counter(struct perf_stat_config *config,
 	int i, ret;
 
 	aggr->val = aggr->ena = aggr->run = 0;
-	init_stats(ps->res_stats);
 
 	if (counter->per_pkg)
 		zero_per_pkg(counter);