perf sleep time profiling: no sched_stat_sleep events?

perf sleep time profiling: no sched_stat_sleep events?

[Milian Wolff]

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Hey all,

sending this here in the hope that it may guide people in avoiding this issue 
in the future:

I have encountered an issue with a recent Arch Linux Kernel (4.7), where the 
the perf script to profile sleep times did not produce any output.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~
perf top -e "sched:sched_stat_*"
# wait for some time
0 sched:sched_stat_wait
0 sched:sched_stat_sleep
0 sched:sched_stat_iowait
0 sched:sched_stat_blocked
4K sched:sched_stat_runtime  

~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The culprit is 


~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cat /proc/sys/kernel/sched_schedstats
0
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Setting that to 1 enables the sched_stat trace points and makes the script 
work again as needed.

I wonder: Could perf print a warning when the user tries to trace these events 
but they are not enabled?

Thanks

-- 
Milian Wolff | milian.wolff@kdab.com | Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt Experts

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