linux-kernel - [tip:perf/urgent] perf: Fix interrupt handler timing harness

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Date:	Fri, 5 Jul 2013 02:54:29 -0700
From:	tip-bot for Stephane Eranian <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, eranian@...gle.com, hpa@...or.com,
	mingo@...nel.org, tglx@...utronix.de
Subject: [tip:perf/urgent] perf: Fix interrupt handler timing harness

Commit-ID:  e5302920da9ef23f9d19d4e9ac85704cc25bee7a
Gitweb:     http://git.kernel.org/tip/e5302920da9ef23f9d19d4e9ac85704cc25bee7a
Author:     Stephane Eranian <eranian@...gle.com>
AuthorDate: Fri, 5 Jul 2013 00:30:11 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 5 Jul 2013 08:54:43 +0200

perf: Fix interrupt handler timing harness

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@...gle.com>
Cc: peterz@...radead.org
Cc: dave.hansen@...ux.intel.com
Cc: ak@...ux.intel.com
Cc: jolsa@...hat.com
Link: http://lkml.kernel.org/r/20130704223010.GA30625@quad
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/events/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1db3af9..1833bc5 100644
--- 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);
 }
 
@@ -232,7 +232,7 @@ DEFINE_PER_CPU(u64, running_sample_length);
 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;
--
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