Re: [PATCH v5 3/4] perf,x86: add Intel RAPL PMU support

[Peter Zijlstra <peterz@infradead.org>]

On Tue, Nov 05, 2013 at 06:01:25PM +0100, Stephane Eranian wrote:
> +static DEFINE_SPINLOCK(rapl_hotplug_lock);

> +static void rapl_exit_cpu(int cpu)
> +{
> +	int i, phys_id = topology_physical_package_id(cpu);
> +
> +	spin_lock(&rapl_hotplug_lock);

> +	spin_unlock(&rapl_hotplug_lock);
> +}
> +
> +static void rapl_init_cpu(int cpu)
> +{
> +	int i, phys_id = topology_physical_package_id(cpu);
> +
> +	spin_lock(&rapl_hotplug_lock);

> +	spin_unlock(&rapl_hotplug_lock);
> +}

> +static int rapl_cpu_starting(int cpu)
> +{
> +	struct rapl_pmu *pmu2;
> +	struct rapl_pmu *pmu1 = per_cpu(rapl_pmu, cpu);
> +	int i, phys_id = topology_physical_package_id(cpu);
> +
> +	if (pmu1)
> +		return 0;
> +
> +	spin_lock(&rapl_hotplug_lock);

> +	spin_unlock(&rapl_hotplug_lock);
> +	return 0;
> +}
> +
> +static int rapl_cpu_dying(int cpu)
> +{
> +	struct rapl_pmu *pmu = per_cpu(rapl_pmu, cpu);
> +	struct perf_event *event, *tmp;
> +
> +	if (!pmu)
> +		return 0;
> +
> +	spin_lock(&rapl_hotplug_lock);

> +	spin_unlock(&rapl_hotplug_lock);
> +	return 0;
> +}
> +
> +static int rapl_cpu_notifier(struct notifier_block *self,
> +			     unsigned long action, void *hcpu)
> +{
> +	unsigned int cpu = (long)hcpu;
> +
> +	/* allocate/free data structure for uncore box */
> +	switch (action & ~CPU_TASKS_FROZEN) {
> +	case CPU_UP_PREPARE:
> +		rapl_cpu_prepare(cpu);
> +		break;
> +	case CPU_STARTING:
> +		rapl_cpu_starting(cpu);
> +		break;
> +	case CPU_UP_CANCELED:
> +	case CPU_DYING:
> +		rapl_cpu_dying(cpu);
> +		break;
> +	case CPU_ONLINE:
> +		kfree(per_cpu(rapl_pmu_kfree, cpu));
> +		per_cpu(rapl_pmu_kfree, cpu) = NULL;
> +		break;
> +	case CPU_DEAD:
> +		per_cpu(rapl_pmu, cpu) = NULL;
> +		break;
> +	default:
> +		break;
> +	}
> +
> +	/* select the cpu that collects uncore events */
> +	switch (action & ~CPU_TASKS_FROZEN) {
> +	case CPU_DOWN_FAILED:
> +	case CPU_STARTING:
> +		rapl_init_cpu(cpu);
> +		break;
> +	case CPU_DOWN_PREPARE:
> +		rapl_exit_cpu(cpu);
> +		break;
> +	default:
> +		break;
> +	}
> +
> +	return NOTIFY_OK;
> +}

What's the point of that rapl_hotplug_lock? It appears all methods its
used from are called from hotplug notifiers and those are fully
serialized by cpu_add_remove_lock.