On Tue, Oct 08, 2019 at 07:21:43PM +0200, gregkh@linuxfoundation.org wrote:
The patch below does not apply to the 5.3-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From b63fd11cced17fcb8e133def29001b0f6aaa5e06 Mon Sep 17 00:00:00 2001 From: Srikar Dronamraju srikar@linux.vnet.ibm.com Date: Wed, 4 Sep 2019 15:17:37 +0530 Subject: [PATCH] perf stat: Reset previous counts on repeat with interval
When using 'perf stat' with repeat and interval option, it shows wrong values for events.
The wrong values will be shown for the first interval on the second and subsequent repetitions.
Without the fix:
# perf stat -r 3 -I 2000 -e faults -e sched:sched_switch -a sleep 5
2.000282489 53 faults 2.000282489 513 sched:sched_switch 4.005478208 3,721 faults 4.005478208 2,666 sched:sched_switch 5.025470933 395 faults 5.025470933 1,307 sched:sched_switch 2.009602825 1,84,46,74,40,73,70,95,47,520 faults <------ 2.009602825 1,84,46,74,40,73,70,95,49,568 sched:sched_switch <------ 4.019612206 4,730 faults 4.019612206 2,746 sched:sched_switch 5.039615484 3,953 faults 5.039615484 1,496 sched:sched_switch 2.000274620 1,84,46,74,40,73,70,95,47,520 faults <------ 2.000274620 1,84,46,74,40,73,70,95,47,520 sched:sched_switch <------ 4.000480342 4,282 faults 4.000480342 2,303 sched:sched_switch 5.000916811 1,322 faults 5.000916811 1,064 sched:sched_switch#
prev_raw_counts is allocated when using intervals. This is used when calculating the difference in the counts of events when using interval.
The current counts are stored in prev_raw_counts to calculate the differences in the next iteration.
On the first interval of the second and subsequent repetitions, prev_raw_counts would be the values stored in the last interval of the previous repetitions, while the current counts will only be for the first interval of the current repetition.
Hence there is a possibility of events showing up as big number.
Fix this by resetting prev_raw_counts whenever perf stat repeats the command.
With the fix:
# perf stat -r 3 -I 2000 -e faults -e sched:sched_switch -a sleep 5
2.019349347 2,597 faults 2.019349347 2,753 sched:sched_switch 4.019577372 3,098 faults 4.019577372 2,532 sched:sched_switch 5.019415481 1,879 faults 5.019415481 1,356 sched:sched_switch 2.000178813 8,468 faults 2.000178813 2,254 sched:sched_switch 4.000404621 7,440 faults 4.000404621 1,266 sched:sched_switch 5.040196079 2,458 faults 5.040196079 556 sched:sched_switch 2.000191939 6,870 faults 2.000191939 1,170 sched:sched_switch 4.000414103 541 faults 4.000414103 902 sched:sched_switch 5.000809863 450 faults 5.000809863 364 sched:sched_switch#
Committer notes:
This was broken since the cset introducing the --interval feature, i.e. --repeat + --interval wasn't tested at that point, add the Fixes tag so that automatic scripts can pick this up.
Fixes: 13370a9b5bb8 ("perf stat: Add interval printing") Signed-off-by: Srikar Dronamraju srikar@linux.vnet.ibm.com Acked-by: Jiri Olsa jolsa@kernel.org Tested-by: Arnaldo Carvalho de Melo acme@redhat.com Tested-by: Ravi Bangoria ravi.bangoria@linux.ibm.com Cc: Namhyung Kim namhyung@kernel.org Cc: Naveen N. Rao naveen.n.rao@linux.vnet.ibm.com Cc: Stephane Eranian eranian@google.com Cc: stable@vger.kernel.org # v3.9+ Link: http://lore.kernel.org/lkml/20190904094738.9558-2-srikar@linux.vnet.ibm.com [ Fixed up conflicts with libperf, i.e. some perf_{evsel,evlist} lost the 'perf' prefix ] Signed-off-by: Arnaldo Carvalho de Melo acme@redhat.com
Conflicts due to the perf_evsel -> evsel rename. Fixed up and queued for all kernels.