perf: arm_pmu: Kill last use of per-CPU cpu_armpmu pointer

Having removed the use of the cpu_armpmu per-CPU variable from the
interrupt handling, the only user left is the BRBE scheduler hook.

It is easy to drop the use of this variable by following the pointer to the
generic PMU structure, and get the arm_pmu structure from there.

Perform the conversion and kill cpu_armpmu altogether.

Suggested-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Will Deacon <will@kernel.org>
Link: https://patch.msgid.link/20251020122944.3074811-27-maz@kernel.org

Author: Marc Zyngier

drivers/perf/arm_pmu.c

@@ -104,7 +104,6 @@ static const struct pmu_irq_ops percpu_pmunmi_ops = {
 	.free_pmuirq = armpmu_free_percpu_pmunmi
 };
 
-DEFINE_PER_CPU(struct arm_pmu *, cpu_armpmu);
 static DEFINE_PER_CPU(int, cpu_irq);
 static DEFINE_PER_CPU(const struct pmu_irq_ops *, cpu_irq_ops);
 
@@ -725,8 +724,6 @@ static int arm_perf_starting_cpu(unsigned int cpu, struct hlist_node *node)
 	if (pmu->reset)
 		pmu->reset(pmu);
 
-	per_cpu(cpu_armpmu, cpu) = pmu;
-
 	irq = armpmu_get_cpu_irq(pmu, cpu);
 	if (irq)
 		per_cpu(cpu_irq_ops, cpu)->enable_pmuirq(irq);
@@ -746,8 +743,6 @@ static int arm_perf_teardown_cpu(unsigned int cpu, struct hlist_node *node)
 	if (irq)
 		per_cpu(cpu_irq_ops, cpu)->disable_pmuirq(irq);
 
-	per_cpu(cpu_armpmu, cpu) = NULL;
-
 	return 0;
 }
 

drivers/perf/arm_pmuv3.c

@@ -1064,7 +1064,7 @@ static int armv8pmu_user_event_idx(struct perf_event *event)
 static void armv8pmu_sched_task(struct perf_event_pmu_context *pmu_ctx,
 				struct task_struct *task, bool sched_in)
 {
-	struct arm_pmu *armpmu = *this_cpu_ptr(&cpu_armpmu);
+	struct arm_pmu *armpmu = to_arm_pmu(pmu_ctx->pmu);
 	struct pmu_hw_events *hw_events = this_cpu_ptr(armpmu->hw_events);
 
 	if (!hw_events->branch_users)

include/linux/perf/arm_pmu.h

@@ -132,8 +132,6 @@ struct arm_pmu {
 
 #define to_arm_pmu(p) (container_of(p, struct arm_pmu, pmu))
 
-DECLARE_PER_CPU(struct arm_pmu *, cpu_armpmu);
-
 u64 armpmu_event_update(struct perf_event *event);
 
 int armpmu_event_set_period(struct perf_event *event);