On Tue, Jun 08, 2021 at 05:26:58PM +0530, Kajol Jain wrote:
> +static int nvdimm_pmu_cpu_offline(unsigned int cpu, struct hlist_node *node)
> +{
> + struct nvdimm_pmu *nd_pmu;
> + u32 target;
> + int nodeid;
> + const struct cpumask *cpumask;
> +
> + nd_pmu = hlist_entry_safe(node, struct nvdimm_pmu, node);
> +
> + /* Clear it, incase given cpu is set in nd_pmu->arch_cpumask */
> + cpumask_test_and_clear_cpu(cpu, &nd_pmu->arch_cpumask);
> +
> + /*
> + * If given cpu is not same as current designated cpu for
> + * counter access, just return.
> + */
> + if (cpu != nd_pmu->cpu)
> + return 0;
> +
> + /* Check for any active cpu in nd_pmu->arch_cpumask */
> + target = cpumask_any(&nd_pmu->arch_cpumask);
> + nd_pmu->cpu = target;
> +
> + /*
> + * Incase we don't have any active cpu in nd_pmu->arch_cpumask,
> + * check in given cpu's numa node list.
> + */
> + if (target >= nr_cpu_ids) {
> + nodeid = cpu_to_node(cpu);
> + cpumask = cpumask_of_node(nodeid);
> + target = cpumask_any_but(cpumask, cpu);
> + nd_pmu->cpu = target;
> +
> + if (target >= nr_cpu_ids)
> + return -1;
> + }
> +
> + return 0;
> +}
> +
> +static int nvdimm_pmu_cpu_online(unsigned int cpu, struct hlist_node *node)
> +{
> + struct nvdimm_pmu *nd_pmu;
> +
> + nd_pmu = hlist_entry_safe(node, struct nvdimm_pmu, node);
> +
> + if (nd_pmu->cpu >= nr_cpu_ids)
> + nd_pmu->cpu = cpu;
> +
> + return 0;
> +}
> +static int nvdimm_pmu_cpu_hotplug_init(struct nvdimm_pmu *nd_pmu)
> +{
> + int nodeid, rc;
> + const struct cpumask *cpumask;
> +
> + /*
> + * Incase cpu hotplug is not handled by arch specific code
> + * they can still provide required cpumask which can be used
> + * to get designatd cpu for counter access.
> + * Check for any active cpu in nd_pmu->arch_cpumask.
> + */
> + if (!cpumask_empty(&nd_pmu->arch_cpumask)) {
> + nd_pmu->cpu = cpumask_any(&nd_pmu->arch_cpumask);
> + } else {
> + /* pick active cpu from the cpumask of device numa node. */
> + nodeid = dev_to_node(nd_pmu->dev);
> + cpumask = cpumask_of_node(nodeid);
> + nd_pmu->cpu = cpumask_any(cpumask);
> + }
> +
> + rc = cpuhp_setup_state_multi(CPUHP_AP_ONLINE_DYN, "perf/nvdimm:online",
> + nvdimm_pmu_cpu_online,
> nvdimm_pmu_cpu_offline);
> +
Did you actually test this hotplug stuff?
That is, create a counter, unplug the CPU the counter was on, and
continue counting? "perf stat -I" is a good option for this, concurrent
with a hotplug.
Because I don't think it's actually correct. The thing is perf core is
strictly per-cpu, and it will place the event on a specific CPU context.
If you then unplug that CPU, nothing will touch the events on that CPU
anymore.
What drivers that span CPUs need to do is call
perf_pmu_migrate_context() whenever the CPU they were assigned to goes
away. Please have a look at arch/x86/events/rapl.c or
arch/x86/events/amd/power.c for relatively simple drivers that have this
property.
