[PATCH] [46/50] ARM: 6989/1: perf: do not start the PMU when no events are

Andi Kleen
2011-07-28T23:46:57Z

From: Will Deacon <will.deacon@arm.com>

[ upstream commit f4f38430c94c38187db73a2cf3892cc8b12a2713 ]
present

armpmu_enable can be called in situations where no events are present
(for example, from the event rotation tick after a profiled task has
exited). In this case, we currently start the PMU anyway which may
leave it active inevitably without any events being monitored.

This patch adds a simple check to the enabling code so that we avoid
starting the PMU when no events are present.

Cc: <stable@kernel.org>
Reported-by: Ashwin Chaugle <ashwinc@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

Index: linux-2.6.35.y/arch/arm/kernel/perf_event.c
===================================================================
--- linux-2.6.35.y.orig/arch/arm/kernel/perf_event.c
+++ linux-2.6.35.y/arch/arm/kernel/perf_event.c
@@ -531,7 +531,7 @@ void
hw_perf_enable(void)
{
/* Enable all of the perf events on hardware. */
- int idx;
+ int idx, enabled = 0;
struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);

if (!armpmu)
@@ -544,9 +544,11 @@ hw_perf_enable(void)
continue;

armpmu->enable(&event->hw, idx);
+ enabled = 1;
}

- armpmu->start();
+ if (enabled)
+ armpmu->start();
}

void