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ARM: 6989/1: perf: do not start the PMU when no events are 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>
This commit is contained in:
Will Deacon 2011-07-01 14:38:12 +01:00 committed by Russell King
parent 178783622c
commit f4f38430c9
1 changed files with 4 additions and 2 deletions
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6
arch/arm/kernel/perf_event.c
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@ -583,7 +583,7 @@ static int armpmu_event_init(struct perf_event *event)
static void armpmu_enable(struct pmu *pmu) static void armpmu_enable(struct pmu *pmu)
{ {
/* Enable all of the perf events on hardware. */ /* 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); struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
if (!armpmu) if (!armpmu)
@ -596,9 +596,11 @@ static void armpmu_enable(struct pmu *pmu)
continue; continue;
armpmu->enable(&event->hw, idx); armpmu->enable(&event->hw, idx);
enabled = 1;
} }
armpmu->start(); if (enabled)
armpmu->start();
} }
static void armpmu_disable(struct pmu *pmu) static void armpmu_disable(struct pmu *pmu)