Patch "perf stat: Fix interval output values" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

perf stat: Fix interval output values

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
perf-stat-fix-interval-output-values.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jiri Olsa <[email protected]>
Date: Wed, 3 Feb 2016 08:43:56 +0100
Subject: perf stat: Fix interval output values

From: Jiri Olsa <[email protected]>

commit 51fd2df1e882a3c2a3f4b6c9ff243a93c9046dba upstream.

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

---
 tools/perf/util/stat.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

@@ -311,6 +311,16 @@ int perf_stat_process_counter(struct per
 
 	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);
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/perf-stat-fix-interval-output-values.patch