arm: perf: Remove PMU locking

Currently the 32-bit arm PMU drivers use the pmu_hw_events::lock spinlock in
their arm_pmu::{start,stop,enable,disable}() callbacks to protect hardware
state and event data.

This locking is not necessary as the perf core code already provides mutual
exclusion, disabling interrupts to serialize against the IRQ handler, and
using perf_event_context::lock to protect against concurrent modifications of
events cross-cpu.

The locking was removed from the arm64 (now PMUv3) PMU driver in commit:

2a0e2a02e4b7 ("arm64: perf: Remove PMU locking")

... and the same reasoning applies to all the 32-bit PMU drivers.

Remove the locking from the 32-bit PMU drivers.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: linux-perf-users@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20231115092805.737822-2-anshuman.khandual@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

1 files changed, 8 insertions, 36 deletions

diff --git a/arch/arm/kernel/perf_event_xscale.c b/arch/arm/kernel/perf_event_xscale.c
index f6cdcacfb96d..7a2ba1c689a7 100644
--- a/arch/arm/kernel/perf_event_xscale.c
+++ b/arch/arm/kernel/perf_event_xscale.c
@@ -203,10 +203,8 @@ xscale1pmu_handle_irq(struct arm_pmu *cpu_pmu)
 
 static void xscale1pmu_enable_event(struct perf_event *event)
 {
-	unsigned long val, mask, evt, flags;
-	struct arm_pmu *cpu_pmu = to_arm_pmu(event->pmu);
+	unsigned long val, mask, evt;
 	struct hw_perf_event *hwc = &event->hw;
-	struct pmu_hw_events *events = this_cpu_ptr(cpu_pmu->hw_events);
 	int idx = hwc->idx;
 
 	switch (idx) {
@@ -229,20 +227,16 @@ static void xscale1pmu_enable_event(struct perf_event *event)
 		return;
 	}
 
-	raw_spin_lock_irqsave(&events->pmu_lock, flags);
 	val = xscale1pmu_read_pmnc();
 	val &= ~mask;
 	val |= evt;
 	xscale1pmu_write_pmnc(val);
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
 }
 
 static void xscale1pmu_disable_event(struct perf_event *event)
 {
-	unsigned long val, mask, evt, flags;
-	struct arm_pmu *cpu_pmu = to_arm_pmu(event->pmu);
+	unsigned long val, mask, evt;
 	struct hw_perf_event *hwc = &event->hw;
-	struct pmu_hw_events *events = this_cpu_ptr(cpu_pmu->hw_events);
 	int idx = hwc->idx;
 
 	switch (idx) {
@@ -263,12 +257,10 @@ static void xscale1pmu_disable_event(struct perf_event *event)
 		return;
 	}
 
-	raw_spin_lock_irqsave(&events->pmu_lock, flags);
 	val = xscale1pmu_read_pmnc();
 	val &= ~mask;
 	val |= evt;
 	xscale1pmu_write_pmnc(val);
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
 }
 
 static int
@@ -300,26 +292,20 @@ static void xscalepmu_clear_event_idx(struct pmu_hw_events *cpuc,
 
 static void xscale1pmu_start(struct arm_pmu *cpu_pmu)
 {
-	unsigned long flags, val;
-	struct pmu_hw_events *events = this_cpu_ptr(cpu_pmu->hw_events);
+	unsigned long val;
 
-	raw_spin_lock_irqsave(&events->pmu_lock, flags);
 	val = xscale1pmu_read_pmnc();
 	val |= XSCALE_PMU_ENABLE;
 	xscale1pmu_write_pmnc(val);
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
 }
 
 static void xscale1pmu_stop(struct arm_pmu *cpu_pmu)
 {
-	unsigned long flags, val;
-	struct pmu_hw_events *events = this_cpu_ptr(cpu_pmu->hw_events);
+	unsigned long val;
 
-	raw_spin_lock_irqsave(&events->pmu_lock, flags);
 	val = xscale1pmu_read_pmnc();
 	val &= ~XSCALE_PMU_ENABLE;
 	xscale1pmu_write_pmnc(val);
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
 }
 
 static inline u64 xscale1pmu_read_counter(struct perf_event *event)
@@ -549,10 +535,8 @@ xscale2pmu_handle_irq(struct arm_pmu *cpu_pmu)
 
 static void xscale2pmu_enable_event(struct perf_event *event)
 {
-	unsigned long flags, ien, evtsel;
-	struct arm_pmu *cpu_pmu = to_arm_pmu(event->pmu);
+	unsigned long ien, evtsel;
 	struct hw_perf_event *hwc = &event->hw;
-	struct pmu_hw_events *events = this_cpu_ptr(cpu_pmu->hw_events);
 	int idx = hwc->idx;
 
 	ien = xscale2pmu_read_int_enable();
@@ -587,18 +571,14 @@ static void xscale2pmu_enable_event(struct perf_event *event)
 		return;
 	}
 
-	raw_spin_lock_irqsave(&events->pmu_lock, flags);
 	xscale2pmu_write_event_select(evtsel);
 	xscale2pmu_write_int_enable(ien);
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
 }
 
 static void xscale2pmu_disable_event(struct perf_event *event)
 {
-	unsigned long flags, ien, evtsel, of_flags;
-	struct arm_pmu *cpu_pmu = to_arm_pmu(event->pmu);
+	unsigned long ien, evtsel, of_flags;
 	struct hw_perf_event *hwc = &event->hw;
-	struct pmu_hw_events *events = this_cpu_ptr(cpu_pmu->hw_events);
 	int idx = hwc->idx;
 
 	ien = xscale2pmu_read_int_enable();
@@ -638,11 +618,9 @@ static void xscale2pmu_disable_event(struct perf_event *event)
 		return;
 	}
 
-	raw_spin_lock_irqsave(&events->pmu_lock, flags);
 	xscale2pmu_write_event_select(evtsel);
 	xscale2pmu_write_int_enable(ien);
 	xscale2pmu_write_overflow_flags(of_flags);
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
 }
 
 static int
@@ -663,26 +641,20 @@ out:
 
 static void xscale2pmu_start(struct arm_pmu *cpu_pmu)
 {
-	unsigned long flags, val;
-	struct pmu_hw_events *events = this_cpu_ptr(cpu_pmu->hw_events);
+	unsigned long val;
 
-	raw_spin_lock_irqsave(&events->pmu_lock, flags);
 	val = xscale2pmu_read_pmnc() & ~XSCALE_PMU_CNT64;
 	val |= XSCALE_PMU_ENABLE;
 	xscale2pmu_write_pmnc(val);
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
 }
 
 static void xscale2pmu_stop(struct arm_pmu *cpu_pmu)
 {
-	unsigned long flags, val;
-	struct pmu_hw_events *events = this_cpu_ptr(cpu_pmu->hw_events);
+	unsigned long val;
 
-	raw_spin_lock_irqsave(&events->pmu_lock, flags);
 	val = xscale2pmu_read_pmnc();
 	val &= ~XSCALE_PMU_ENABLE;
 	xscale2pmu_write_pmnc(val);
-	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
 }
 
 static inline u64 xscale2pmu_read_counter(struct perf_event *event)