Messages in this thread | | | Date | Thu, 15 Dec 2022 09:43:55 +0800 | From | Leo Yan <> | Subject | Re: [PATCH] perf stat: Do not delay the workload with --delay |
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On Mon, Dec 12, 2022 at 03:08:20PM -0800, Namhyung Kim wrote: > The -D/--delay option is to delay the measure after the program starts. > But the current code goes to sleep before starting the program so the > program is delayed too. This is not the intention, let's fix it. > > Before: > > $ time sudo ./perf stat -a -e cycles -D 3000 sleep 4 > Events disabled > Events enabled > > Performance counter stats for 'system wide': > > 4,326,949,337 cycles > > 4.007494118 seconds time elapsed > > real 0m7.474s > user 0m0.356s > sys 0m0.120s > > It ran the workload for 4 seconds and gave the 3 second delay. So it > should skip the first 3 second and measure the last 1 second only. But > as you can see, it delays 3 seconds and ran the workload after that for > 4 seconds. So the total time (real) was 7 seconds. > > After: > > $ time sudo ./perf stat -a -e cycles -D 3000 sleep 4 > Events disabled > Events enabled > > Performance counter stats for 'system wide': > > 1,063,551,013 cycles > > 1.002769510 seconds time elapsed > > real 0m4.484s > user 0m0.385s > sys 0m0.086s > > The bug was introduced when it changed enablement of system-wide events > with a command line workload. But it should've considered the initial > delay case. The code was reworked since then (in bb8bc52e7578) so I'm > afraid it won't be applied cleanly. > > Fixes: d0a0a511493d ("perf stat: Fix forked applications enablement of counters") > Cc: Sumanth Korikkar <sumanthk@linux.ibm.com> > Cc: Thomas Richter <tmricht@linux.ibm.com> > Reported-by: Kevin Nomura <nomurak@google.com> > Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Reviewed-by: Leo Yan <leo.yan@linaro.org>
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