[PATCH 3.10 37/40] perf: Fix interrupt handler timing harness

Greg Kroah-Hartman
2014-06-09T22:50:00Z

From: Stephane Eranian <eranian@google.com>

commit e5302920da9ef23f9d19d4e9ac85704cc25bee7a upstream.

This patch fixes a serious bug in:

14c63f17b1fd perf: Drop sample rate when sampling is too slow

There was an misunderstanding on the API of the do_div()
macro. It returns the remainder of the division and this
was not what the function expected leading to disabling the
interrupt latency watchdog.

This patch also remove a duplicate assignment in
perf_sample_event_took().

Signed-off-by: Stephane Eranian <eranian@google.com>
Cc: peterz@infradead.org
Cc: dave.hansen@linux.intel.com
Cc: ak@linux.intel.com
Cc: jolsa@redhat.com
Link: http://lkml.kernel.org/r/20130704223010.GA30625@quad
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Weng Meiling <wengmeiling.weng@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
kernel/events/core.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -182,7 +182,7 @@ void update_perf_cpu_limits(void)
u64 tmp = perf_sample_period_ns;

tmp *= sysctl_perf_cpu_time_max_percent;
- tmp = do_div(tmp, 100);
+ do_div(tmp, 100);
atomic_set(&perf_sample_allowed_ns, tmp);
}

@@ -230,7 +230,7 @@ DEFINE_PER_CPU(u64, running_sample_lengt
void perf_sample_event_took(u64 sample_len_ns)
{
u64 avg_local_sample_len;
- u64 local_samples_len = __get_cpu_var(running_sample_length);
+ u64 local_samples_len;

if (atomic_read(&perf_sample_allowed_ns) == 0)
return;