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arm64: perf: Remove PMU locking

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The PMU is disabled and enabled, and the counters are programmed from
contexts where interrupts or preemption is disabled.

The functions to toggle the PMU and to program the PMU counters access the
registers directly and don't access data modified by the interrupt handler.
That, and the fact that they're always called from non-preemptible
contexts, means that we don't need to disable interrupts or use a spinlock.

[Alexandru E.: Explained why locking is not needed, removed WARN_ONs]

Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
Tested-by: Sumit Garg <sumit.garg@linaro.org> (Developerbox)
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20200924110706.254996-4-alexandru.elisei@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Julien Thierry 2020-09-24 12:07:02 +01:00 committed by Will Deacon
parent 0fdf1bb759
commit 2a0e2a02e4
1 changed files with 0 additions and 28 deletions
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28
arch/arm64/kernel/perf_event.c
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@ -691,15 +691,10 @@ 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
@ -720,21 +715,10 @@ 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
*/
@ -744,30 +728,18 @@ 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);
/* Enable all counters */
armv8pmu_pmcr_write(armv8pmu_pmcr_read() | ARMV8_PMU_PMCR_E);
raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
}
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);
/* Disable all counters */
armv8pmu_pmcr_write(armv8pmu_pmcr_read() & ~ARMV8_PMU_PMCR_E);
raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
}
static irqreturn_t armv8pmu_handle_irq(struct arm_pmu *cpu_pmu)