Messages in this thread | | | Date | Fri, 27 Jan 2012 11:03:21 -0600 | From | Andrew Steets <> | Subject | perf: prctl(PR_TASK_PERF_EVENTS_DISABLE) has no effect |
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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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