[PATCH v2 4/9] arm: perf: Remove Remove PMU locking

Julien Thierry julien.thierry at arm.com
Fri Mar 22 09:23:59 PDT 2019


Since the PMU interrupt saves and restores the value of the selector
register, there is no need to serialize register accesses against the
interrupt contexts.

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: Russell King <linux at armlinux.org.uk>
---
 arch/arm/kernel/perf_event_v7.c | 56 +++--------------------------------------
 1 file changed, 4 insertions(+), 52 deletions(-)

diff --git a/arch/arm/kernel/perf_event_v7.c b/arch/arm/kernel/perf_event_v7.c
index c3da7a5..cb3b7a4 100644
--- a/arch/arm/kernel/perf_event_v7.c
+++ b/arch/arm/kernel/perf_event_v7.c
@@ -882,10 +882,8 @@ static void armv7_pmnc_dump_regs(struct arm_pmu *cpu_pmu)

 static void armv7pmu_enable_event(struct perf_event *event)
 {
-	unsigned long flags;
 	struct hw_perf_event *hwc = &event->hw;
 	struct arm_pmu *cpu_pmu = to_arm_pmu(event->pmu);
-	struct pmu_hw_events *events = this_cpu_ptr(cpu_pmu->hw_events);
 	int idx = hwc->idx;

 	if (!armv7_pmnc_counter_valid(cpu_pmu, idx)) {
@@ -898,7 +896,6 @@ static void armv7pmu_enable_event(struct perf_event *event)
 	 * 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
@@ -922,16 +919,12 @@ static void armv7pmu_enable_event(struct perf_event *event)
 	 * Enable counter
 	 */
 	armv7_pmnc_enable_counter(idx);
-
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
 }

 static void armv7pmu_disable_event(struct perf_event *event)
 {
-	unsigned long flags;
 	struct hw_perf_event *hwc = &event->hw;
 	struct arm_pmu *cpu_pmu = to_arm_pmu(event->pmu);
-	struct pmu_hw_events *events = this_cpu_ptr(cpu_pmu->hw_events);
 	int idx = hwc->idx;

 	if (!armv7_pmnc_counter_valid(cpu_pmu, idx)) {
@@ -941,11 +934,6 @@ static void armv7pmu_disable_event(struct perf_event *event)
 	}

 	/*
-	 * Disable counter and interrupt
-	 */
-	raw_spin_lock_irqsave(&events->pmu_lock, flags);
-
-	/*
 	 * Disable counter
 	 */
 	armv7_pmnc_disable_counter(idx);
@@ -954,8 +942,6 @@ static void armv7pmu_disable_event(struct perf_event *event)
 	 * Disable interrupt for this counter
 	 */
 	armv7_pmnc_disable_intens(idx);
-
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
 }

 static irqreturn_t armv7pmu_handle_irq(struct arm_pmu *cpu_pmu)
@@ -1026,24 +1012,18 @@ static irqreturn_t armv7pmu_handle_irq(struct arm_pmu *cpu_pmu)

 static void armv7pmu_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 */
 	armv7_pmnc_write(armv7_pmnc_read() | ARMV7_PMNC_E);
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
+	preempt_enable();
 }

 static void armv7pmu_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 */
 	armv7_pmnc_write(armv7_pmnc_read() & ~ARMV7_PMNC_E);
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
+	preempt_enable();
 }

 static int armv7pmu_get_event_idx(struct pmu_hw_events *cpuc,
@@ -1509,14 +1489,8 @@ static void krait_clearpmu(u32 config_base)

 static void krait_pmu_disable_event(struct perf_event *event)
 {
-	unsigned long flags;
 	struct hw_perf_event *hwc = &event->hw;
 	int idx = hwc->idx;
-	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 */
 	armv7_pmnc_disable_counter(idx);
@@ -1529,23 +1503,17 @@ static void krait_pmu_disable_event(struct perf_event *event)

 	/* Disable interrupt for this counter */
 	armv7_pmnc_disable_intens(idx);
-
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
 }

 static void krait_pmu_enable_event(struct perf_event *event)
 {
-	unsigned long flags;
 	struct hw_perf_event *hwc = &event->hw;
 	int idx = hwc->idx;
-	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 */
 	armv7_pmnc_disable_counter(idx);
@@ -1565,8 +1533,6 @@ static void krait_pmu_enable_event(struct perf_event *event)

 	/* Enable counter */
 	armv7_pmnc_enable_counter(idx);
-
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
 }

 static void krait_pmu_reset(void *info)
@@ -1842,14 +1808,8 @@ static void scorpion_clearpmu(u32 config_base)

 static void scorpion_pmu_disable_event(struct perf_event *event)
 {
-	unsigned long flags;
 	struct hw_perf_event *hwc = &event->hw;
 	int idx = hwc->idx;
-	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 */
 	armv7_pmnc_disable_counter(idx);
@@ -1862,23 +1822,17 @@ static void scorpion_pmu_disable_event(struct perf_event *event)

 	/* Disable interrupt for this counter */
 	armv7_pmnc_disable_intens(idx);
-
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
 }

 static void scorpion_pmu_enable_event(struct perf_event *event)
 {
-	unsigned long flags;
 	struct hw_perf_event *hwc = &event->hw;
 	int idx = hwc->idx;
-	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 */
 	armv7_pmnc_disable_counter(idx);
@@ -1898,8 +1852,6 @@ static void scorpion_pmu_enable_event(struct perf_event *event)

 	/* Enable counter */
 	armv7_pmnc_enable_counter(idx);
-
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
 }

 static void scorpion_pmu_reset(void *info)
--
1.9.1



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