linux-kernel - [PATCH][perf/urgent] perf stat: Fix interval output values

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Date:	Wed,  3 Feb 2016 08:43:56 +0100
From:	Jiri Olsa <jolsa@...nel.org>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH][perf/urgent] perf stat: Fix interval output values

We broke interval data displays with commit:
  3f416f22d1e2 perf stat: Do not clean event's private stats

This commit removed stats cleaning, which is important
for '-r' option to carry counters data over the whole
run. But it's necessary to clean it for interval mode,
otherwise the displayed value is avg of all previous
values.

Before:
  $ perf stat -e cycles -a -I 1000 record
  #           time             counts unit events
       1.000240796         75,216,287      cycles
       2.000512791        107,823,524      cycles

  $ perf stat report
  #           time             counts unit events
       1.000240796         75,216,287      cycles
       2.000512791         91,519,906      cycles

Now:
  $ perf stat report
  #           time             counts unit events
       1.000240796         75,216,287      cycles
       2.000512791        107,823,524      cycles

Notice the second value being bigger (91,.. < 107,..).

This could be easily verified by using perf script which
displays raw stat data:

  $ perf script
  CPU   THREAD             VAL             ENA             RUN            TIME EVENT
    0       -1        23855779      1000209530      1000209530      1000240796 cycles
    1       -1        33340397      1000224964      1000224964      1000240796 cycles
    2       -1        15835415      1000226695      1000226695      1000240796 cycles
    3       -1         2184696      1000228245      1000228245      1000240796 cycles
    0       -1        97014312      2000514533      2000514533      2000512791 cycles
    1       -1        46121497      2000543795      2000543795      2000512791 cycles
    2       -1        32269530      2000543566      2000543566      2000512791 cycles
    3       -1         7634472      2000544108      2000544108      2000512791 cycles

The sum of the first 4 values is the first interval
aggregated value:
  23855779 + 33340397 + 15835415 + 2184696 = 75,216,287

The sum of the second 4 values minus first value is
the second interval aggregated value:
  97014312 + 46121497 + 32269530 + 7634472 - 75216287 = 107,823,524

Link: http://lkml.kernel.org/n/tip-4xawgmi82euqnq9t87l2l1in@git.kernel.org
Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
 tools/perf/util/stat.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tools/perf/util/stat.c b/tools/perf/util/stat.c
index beeed0bd3bee..4d9b481cf3b6 100644
--- a/tools/perf/util/stat.c
+++ b/tools/perf/util/stat.c
@@ -311,6 +311,16 @@ int perf_stat_process_counter(struct perf_stat_config *config,
 
 	aggr->val = aggr->ena = aggr->run = 0;
 
+	/*
+	 * We calculate counter's data every interval,
+	 * and the display code shows ps->res_stats
+	 * avg value. We need to zero the stats for
+	 * interval mode, otherwise overall avg running
+	 * averages will be shown for each interval.
+	 */
+	if (config->interval)
+		init_stats(ps->res_stats);
+
 	if (counter->per_pkg)
 		zero_per_pkg(counter);
 
-- 
2.4.3