Add the --repeat <n> feature to perf stat, which repeats a given
command up to a 100 times, collects the stats and calculates an
average and a stddev.
For example, the following oneliner 'perf stat' command runs hackbench
5 times and prints a tabulated result of all metrics, with averages
and noise levels (in percentage) printed:
aldebaran:~/linux/linux/tools/perf> ./perf stat --repeat 5 ~/hackbench 10
Time: 0.117
Time: 0.108
Time: 0.089
Time: 0.088
Time: 0.100
Performance counter stats for '/home/mingo/hackbench 10' (5 runs):
1243.989586 task-clock-msecs # 10.460 CPUs ( +- 4.720% )
47706 context-switches # 0.038 M/sec ( +- 19.706% )
387 CPU-migrations # 0.000 M/sec ( +- 3.608% )
17793 page-faults # 0.014 M/sec ( +- 0.354% )
3770941606 cycles # 3031.329 M/sec ( +- 4.621% )
1566372416 instructions # 0.415 IPC ( +- 2.703% )
16783421 cache-references # 13.492 M/sec ( +- 5.202% )
7128590 cache-misses # 5.730 M/sec ( +- 7.420% )
0.118924455 seconds time elapsed.
The goal of this feature is to allow the reliance on these accurate
statistics and to know how many times a command has to be repeated
for the noise to go down to an acceptable level.
(The -v option can be used to see a line printed out as each run progresses.)
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
42202dd56c