prctl(PR_TASK_PERF_EVENTS_DISABLE) doesn't appear to disable perf event
counters. Here is a demonstration program:
#include <linux/prctl.h>
void loop_events_disabled() {
volatile int x;
int i;
for (i = 0; i < 1000000000; i++)
x = i;
return;
}
void loop_events_enabled() {
volatile int x;
int i;
for (i = 0; i < 1000000000; i++)
x = i;
return;
}
int main(int argc, char **argv) {
prctl(PR_TASK_PERF_EVENTS_ENABLE);
loop_events_enabled();
prctl(PR_TASK_PERF_EVENTS_DISABLE);
loop_events_disabled();
}
I would not expect to see loop_events_disabled() show up in the profile
as reported by perf report, but it does.
$ perf record ./a.out
$ perf report -n --stdio
# Events: 3K cycles
#
# Overhead Samples Command Shared Object Symbol
# ........ .......... ....... ................. ....................
#
51.80% 1679 a.out a.out [.] loop_events_enabled
48.07% 1578 a.out a.out [.] loop_events_disabled
0.03% 5 a.out [kernel.kallsyms] [k] intel_pmu_enable_all
0.03% 1 a.out [kernel.kallsyms] [k] sched_clock
0.03% 1 a.out [kernel.kallsyms] [k] ktime_get
0.03% 1 a.out [kernel.kallsyms] [k] update_cpu_load
0.01% 1 a.out [sunrpc] [k] generic_match
I have tested this on several kernels including 3.3rc1. Can anyone tell
me if I'm using this wrong or if this is a bug?
-Andrew
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