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Commit da4e4f18 authored by Lorenzo Pieralisi's avatar Lorenzo Pieralisi Committed by Will Deacon
Browse files

drivers/perf: arm_pmu: implement CPU_PM notifier 



When a CPU is suspended (either through suspend-to-RAM or CPUidle),
its PMU registers content can be lost, which means that counters
registers values that were initialized on power down entry have to be
reprogrammed on power-up to make sure the counters set-up is preserved
(ie on power-up registers take the reset values on Cold or Warm reset,
which can be architecturally UNKNOWN).

To guarantee seamless profiling conditions across a core power down
this patch adds a CPU PM notifier to ARM pmus, that upon CPU PM
entry/exit from low-power states saves/restores the pmu registers
set-up (by using the ARM perf API), so that the power-down/up cycle does
not affect the perf behaviour (apart from a black-out period between
power-up/down CPU PM notifications that is unavoidable).

Cc: Will Deacon <will.deacon@arm.com>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Acked-by: default avatarAshwin Chaugule <ashwin.chaugule@linaro.org>
Acked-by: default avatarKevin Hilman <khilman@baylibre.com>
Signed-off-by: default avatarLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 94085fe5

drivers/perf/arm_pmu.c

+95 −0
Original line number Diff line number Diff line
@@ -13,6 +13,7 @@ 


#include <linux/bitmap.h>

#include <linux/cpumask.h>

#include <linux/cpu_pm.h>

#include <linux/export.h>

#include <linux/kernel.h>

#include <linux/of_device.h>
@@ -710,6 +711,93 @@ static int cpu_pmu_notify(struct notifier_block *b, unsigned long action, 
	return NOTIFY_OK;

}



#ifdef CONFIG_CPU_PM

static void cpu_pm_pmu_setup(struct arm_pmu *armpmu, unsigned long cmd)

{

	struct pmu_hw_events *hw_events = this_cpu_ptr(armpmu->hw_events);

	struct perf_event *event;

	int idx;



	for (idx = 0; idx < armpmu->num_events; idx++) {

		/*

		 * If the counter is not used skip it, there is no

		 * need of stopping/restarting it.

		 */

		if (!test_bit(idx, hw_events->used_mask))

			continue;



		event = hw_events->events[idx];



		switch (cmd) {

		case CPU_PM_ENTER:

			/*

			 * Stop and update the counter

			 */

			armpmu_stop(event, PERF_EF_UPDATE);

			break;

		case CPU_PM_EXIT:

		case CPU_PM_ENTER_FAILED:

			 /* Restore and enable the counter */

			armpmu_start(event, PERF_EF_RELOAD);

			break;

		default:

			break;

		}

	}

}



static int cpu_pm_pmu_notify(struct notifier_block *b, unsigned long cmd,

			     void *v)

{

	struct arm_pmu *armpmu = container_of(b, struct arm_pmu, cpu_pm_nb);

	struct pmu_hw_events *hw_events = this_cpu_ptr(armpmu->hw_events);

	int enabled = bitmap_weight(hw_events->used_mask, armpmu->num_events);



	if (!cpumask_test_cpu(smp_processor_id(), &armpmu->supported_cpus))

		return NOTIFY_DONE;



	/*

	 * Always reset the PMU registers on power-up even if

	 * there are no events running.

	 */

	if (cmd == CPU_PM_EXIT && armpmu->reset)

		armpmu->reset(armpmu);



	if (!enabled)

		return NOTIFY_OK;



	switch (cmd) {

	case CPU_PM_ENTER:

		armpmu->stop(armpmu);

		cpu_pm_pmu_setup(armpmu, cmd);

		break;

	case CPU_PM_EXIT:

		cpu_pm_pmu_setup(armpmu, cmd);

	case CPU_PM_ENTER_FAILED:

		armpmu->start(armpmu);

		break;

	default:

		return NOTIFY_DONE;

	}



	return NOTIFY_OK;

}



static int cpu_pm_pmu_register(struct arm_pmu *cpu_pmu)

{

	cpu_pmu->cpu_pm_nb.notifier_call = cpu_pm_pmu_notify;

	return cpu_pm_register_notifier(&cpu_pmu->cpu_pm_nb);

}



static void cpu_pm_pmu_unregister(struct arm_pmu *cpu_pmu)

{

	cpu_pm_unregister_notifier(&cpu_pmu->cpu_pm_nb);

}

#else

static inline int cpu_pm_pmu_register(struct arm_pmu *cpu_pmu) { return 0; }

static inline void cpu_pm_pmu_unregister(struct arm_pmu *cpu_pmu) { }

#endif



static int cpu_pmu_init(struct arm_pmu *cpu_pmu)

{

	int err;
@@ -725,6 +813,10 @@ static int cpu_pmu_init(struct arm_pmu *cpu_pmu) 
	if (err)

		goto out_hw_events;



	err = cpu_pm_pmu_register(cpu_pmu);

	if (err)

		goto out_unregister;



	for_each_possible_cpu(cpu) {

		struct pmu_hw_events *events = per_cpu_ptr(cpu_hw_events, cpu);

		raw_spin_lock_init(&events->pmu_lock);
@@ -746,6 +838,8 @@ static int cpu_pmu_init(struct arm_pmu *cpu_pmu) 


	return 0;



out_unregister:

	unregister_cpu_notifier(&cpu_pmu->hotplug_nb);

out_hw_events:

	free_percpu(cpu_hw_events);

	return err;
@@ -753,6 +847,7 @@ static int cpu_pmu_init(struct arm_pmu *cpu_pmu) 


static void cpu_pmu_destroy(struct arm_pmu *cpu_pmu)

{

	cpu_pm_pmu_unregister(cpu_pmu);

	unregister_cpu_notifier(&cpu_pmu->hotplug_nb);

	free_percpu(cpu_pmu->hw_events);

}

include/linux/perf/arm_pmu.h

+1 −0
Original line number Diff line number Diff line
@@ -108,6 +108,7 @@ struct arm_pmu { 
	struct platform_device	*plat_device;

	struct pmu_hw_events	__percpu *hw_events;

	struct notifier_block	hotplug_nb;

	struct notifier_block	cpu_pm_nb;

};



#define to_arm_pmu(p) (container_of(p, struct arm_pmu, pmu))