From: Andrew Steets <asteets@rgmadvisors.com>
To: linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
Paul Mackerras <paulus@samba.org>, Ingo Molnar <mingo@elte.hu>,
Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Subject: perf: prctl(PR_TASK_PERF_EVENTS_DISABLE) has no effect
Date: Fri, 27 Jan 2012 11:03:21 -0600 [thread overview]
Message-ID: <4F22D8D9.3010108@rgmadvisors.com> (raw)
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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next reply other threads:[~2012-01-27 17:03 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-27 17:03 Andrew Steets [this message]
2012-01-27 17:12 ` perf: prctl(PR_TASK_PERF_EVENTS_DISABLE) has no effect Peter Zijlstra
2012-01-27 20:06 ` Andrew Steets
2012-01-27 21:34 ` Peter Zijlstra
2012-01-28 12:01 ` Ingo Molnar
2012-01-28 23:48 ` Andrew Steets
2012-01-29 16:32 ` Ingo Molnar
2012-01-29 17:50 ` Gleb Natapov
2012-01-30 9:52 ` Peter Zijlstra
2012-01-30 10:11 ` Ingo Molnar
2012-01-30 11:01 ` Peter Zijlstra
2012-01-30 11:31 ` Ingo Molnar
2012-01-30 13:45 ` Peter Zijlstra
2012-01-30 13:58 ` Ingo Molnar
2012-01-30 15:30 ` Arnaldo Carvalho de Melo
2012-01-30 15:29 ` Arnaldo Carvalho de Melo
2012-02-01 19:03 ` Frederic Weisbecker
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