From: Milian Wolff <milian.wolff@kdab.com>
To: linux-perf-users@vger.kernel.org
Subject: Duplication of sched events
Date: Thu, 06 Oct 2016 18:14:16 +0200 [thread overview]
Message-ID: <2304161.71JrnPZhhs@milian-kdab2> (raw)
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Hey all,
I noticed the following strange behavior, which applies to most of the sched
trace events, most notably sched_wakeup and sched_stat_*:
~~~~~~~~
#include <unistd.h>
int main()
{
for (int i = 0; i < 100; ++i) {
usleep(10);
}
}
~~~~~~~~
~~~~~~~~
$ perf record -e sched:sched_wakeup --event=syscalls:sys_{enter,exit}
_nanosleep ./a.out
a.out 16841 [007] 24360.139137: syscalls:sys_enter_nanosleep: rqtp:
0x7ffda95e0c20, rmtp: 0x00000000
swapper 0 [007] 24360.139201: sched:sched_wakeup:
a.out:16841 [120] success=1 CPU:007
swapper 0 [007] 24360.139201: sched:sched_wakeup:
a.out:16841 [120] success=1 CPU:007
swapper 0 [007] 24360.139202: sched:sched_wakeup:
a.out:16841 [120] success=1 CPU:007
swapper 0 [007] 24360.139202: sched:sched_wakeup:
a.out:16841 [120] success=1 CPU:007
swapper 0 [007] 24360.139202: sched:sched_wakeup:
a.out:16841 [120] success=1 CPU:007
swapper 0 [007] 24360.139202: sched:sched_wakeup:
a.out:16841 [120] success=1 CPU:007
swapper 0 [007] 24360.139203: sched:sched_wakeup:
a.out:16841 [120] success=1 CPU:007
swapper 0 [007] 24360.139203: sched:sched_wakeup:
a.out:16841 [120] success=1 CPU:007
a.out 16841 [007] 24360.139206: syscalls:sys_exit_nanosleep: 0x0
a.out 16841 [007] 24360.139206: syscalls:sys_enter_nanosleep: rqtp:
0x7ffda95e0c20, rmtp: 0x00000000
swapper 0 [007] 24360.139267: sched:sched_wakeup:
a.out:16841 [120] success=1 CPU:007
swapper 0 [007] 24360.139268: sched:sched_wakeup:
a.out:16841 [120] success=1 CPU:007
swapper 0 [007] 24360.139268: sched:sched_wakeup:
a.out:16841 [120] success=1 CPU:007
swapper 0 [007] 24360.139268: sched:sched_wakeup:
a.out:16841 [120] success=1 CPU:007
swapper 0 [007] 24360.139268: sched:sched_wakeup:
a.out:16841 [120] success=1 CPU:007
swapper 0 [007] 24360.139269: sched:sched_wakeup:
a.out:16841 [120] success=1 CPU:007
swapper 0 [007] 24360.139269: sched:sched_wakeup:
a.out:16841 [120] success=1 CPU:007
swapper 0 [007] 24360.139269: sched:sched_wakeup:
a.out:16841 [120] success=1 CPU:007
a.out 16841 [007] 24360.139270: syscalls:sys_exit_nanosleep: 0x0
...
# repeated like this
~~~~~~
Note how I get eight sched_wakeup events, all for the same cpu. This seems to
be related to the number of cores on my system:
~~~~~
$ nproc
8
~~~~~
On a quad-core machine, I get them four times.
Interestingly, tracing system-wide "fixes" this behavior:
~~~~~
$ perf record -e sched:sched_wakeup --event=syscalls:sys_{enter,exit}
_nanosleep -a ./a.out
$ perf script |& grep a.out | head
a.out 16978 [006] 24514.874484: syscalls:sys_enter_nanosleep: rqtp:
0x7ffc44f450e0, rmtp: 0x00000000
swapper 0 [006] 24514.874547: sched:sched_wakeup:
a.out:16978 [120] success=1 CPU:006
a.out 16978 [006] 24514.874549: syscalls:sys_exit_nanosleep: 0x0
a.out 16978 [006] 24514.874549: syscalls:sys_enter_nanosleep: rqtp:
0x7ffc44f450e0, rmtp: 0x00000000
swapper 0 [006] 24514.874611: sched:sched_wakeup:
a.out:16978 [120] success=1 CPU:006
a.out 16978 [006] 24514.874612: syscalls:sys_exit_nanosleep: 0x0
~~~~~
I think this is a bug. Can someone clarify where it could come from, then I
could try to fix it.
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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