[PATCH v2 2/9] arm64: perf: Remove PMU locking

Julien Thierry julien.thierry at arm.com
Fri Mar 22 09:23:57 PDT 2019


Since the PMU driver uses direct registers for counter
setup/manipulation, locking around these operations is no longer needed.

For operations that can be called with interrupts enabled, preemption
still needs to be disabled to ensure the programming of the PMU is
done on the expected CPU and not migrated mid-programming.

Signed-off-by: Julien Thierry <julien.thierry at arm.com>
Cc: Will Deacon <will.deacon at arm.com>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Ingo Molnar <mingo at redhat.com>
Cc: Arnaldo Carvalho de Melo <acme at kernel.org>
Cc: Alexander Shishkin <alexander.shishkin at linux.intel.com>
Cc: Jiri Olsa <jolsa at redhat.com>
Cc: Namhyung Kim <namhyung at kernel.org>
Cc: Catalin Marinas <catalin.marinas at arm.com>
---
 arch/arm64/kernel/perf_event.c | 32 ++++----------------------------
 1 file changed, 4 insertions(+), 28 deletions(-)

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 63d45e2..bae4242 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -659,15 +659,10 @@ static inline u32 armv8pmu_getreset_flags(void)

 static void armv8pmu_enable_event(struct perf_event *event)
 {
-	unsigned long flags;
-	struct arm_pmu *cpu_pmu = to_arm_pmu(event->pmu);
-	struct pmu_hw_events *events = this_cpu_ptr(cpu_pmu->hw_events);
-
 	/*
 	 * Enable counter and interrupt, and set the counter to count
 	 * the event that we're interested in.
 	 */
-	raw_spin_lock_irqsave(&events->pmu_lock, flags);

 	/*
 	 * Disable counter
@@ -688,21 +683,10 @@ static void armv8pmu_enable_event(struct perf_event *event)
 	 * Enable counter
 	 */
 	armv8pmu_enable_event_counter(event);
-
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
 }

 static void armv8pmu_disable_event(struct perf_event *event)
 {
-	unsigned long flags;
-	struct arm_pmu *cpu_pmu = to_arm_pmu(event->pmu);
-	struct pmu_hw_events *events = this_cpu_ptr(cpu_pmu->hw_events);
-
-	/*
-	 * Disable counter and interrupt
-	 */
-	raw_spin_lock_irqsave(&events->pmu_lock, flags);
-
 	/*
 	 * Disable counter
 	 */
@@ -712,30 +696,22 @@ static void armv8pmu_disable_event(struct perf_event *event)
 	 * Disable interrupt for this counter
 	 */
 	armv8pmu_disable_event_irq(event);
-
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
 }

 static void armv8pmu_start(struct arm_pmu *cpu_pmu)
 {
-	unsigned long flags;
-	struct pmu_hw_events *events = this_cpu_ptr(cpu_pmu->hw_events);
-
-	raw_spin_lock_irqsave(&events->pmu_lock, flags);
+	preempt_disable();
 	/* Enable all counters */
 	armv8pmu_pmcr_write(armv8pmu_pmcr_read() | ARMV8_PMU_PMCR_E);
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
+	preempt_enable();
 }

 static void armv8pmu_stop(struct arm_pmu *cpu_pmu)
 {
-	unsigned long flags;
-	struct pmu_hw_events *events = this_cpu_ptr(cpu_pmu->hw_events);
-
-	raw_spin_lock_irqsave(&events->pmu_lock, flags);
+	preempt_disable();
 	/* Disable all counters */
 	armv8pmu_pmcr_write(armv8pmu_pmcr_read() & ~ARMV8_PMU_PMCR_E);
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
+	preempt_enable();
 }

 static irqreturn_t armv8pmu_handle_irq(struct arm_pmu *cpu_pmu)
--
1.9.1



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