powerpc/perf/hv-gpci: Add cpu hotplug support

Patch here adds cpu hotplug functions to hv_gpci pmu.
A new cpuhp_state "CPUHP_AP_PERF_POWERPC_HV_GPCI_ONLINE" enum
is added.

The online callback function updates the cpumask only if its
empty. As the primary intention of adding hotplug support
is to designate a CPU to make HCALL to collect the
counter data.

The offline function test and clear corresponding cpu in a cpumask
and update cpumask to any other active cpu.

Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201003074943.338618-4-kjain@linux.ibm.com

diff --git a/arch/powerpc/perf/hv-gpci.c b/arch/powerpc/perf/hv-gpci.c
index 1667315..1bca0c1 100644 (file)
--- a/arch/powerpc/perf/hv-gpci.c
+++ b/arch/powerpc/perf/hv-gpci.c
@@ -48,6 +48,8 @@ EVENT_DEFINE_RANGE_FORMAT(length, config1, 24, 31);
 /* u32, byte offset */
 EVENT_DEFINE_RANGE_FORMAT(offset, config1, 32, 63);
 
+static cpumask_t hv_gpci_cpumask;
+
 static struct attribute *format_attrs[] = {
        &format_attr_request.attr,
        &format_attr_starting_index.attr,
@@ -266,6 +268,45 @@ static struct pmu h_gpci_pmu = {
        .capabilities = PERF_PMU_CAP_NO_EXCLUDE,
 };
 
+static int ppc_hv_gpci_cpu_online(unsigned int cpu)
+{
+       if (cpumask_empty(&hv_gpci_cpumask))
+               cpumask_set_cpu(cpu, &hv_gpci_cpumask);
+
+       return 0;
+}
+
+static int ppc_hv_gpci_cpu_offline(unsigned int cpu)
+{
+       int target;
+
+       /* Check if exiting cpu is used for collecting gpci events */
+       if (!cpumask_test_and_clear_cpu(cpu, &hv_gpci_cpumask))
+               return 0;
+
+       /* Find a new cpu to collect gpci events */
+       target = cpumask_last(cpu_active_mask);
+
+       if (target < 0 || target >= nr_cpu_ids) {
+               pr_err("hv_gpci: CPU hotplug init failed\n");
+               return -1;
+       }
+
+       /* Migrate gpci events to the new target */
+       cpumask_set_cpu(target, &hv_gpci_cpumask);
+       perf_pmu_migrate_context(&h_gpci_pmu, cpu, target);
+
+       return 0;
+}
+
+static int hv_gpci_cpu_hotplug_init(void)
+{
+       return cpuhp_setup_state(CPUHP_AP_PERF_POWERPC_HV_GPCI_ONLINE,
+                         "perf/powerpc/hv_gcpi:online",
+                         ppc_hv_gpci_cpu_online,
+                         ppc_hv_gpci_cpu_offline);
+}
+
 static int hv_gpci_init(void)
 {
        int r;
@@ -286,6 +327,11 @@ static int hv_gpci_init(void)
                return -ENODEV;
        }
 
+       /* init cpuhotplug */
+       r = hv_gpci_cpu_hotplug_init();
+       if (r)
+               return r;
+
        /* sampling not supported */
        h_gpci_pmu.capabilities |= PERF_PMU_CAP_NO_INTERRUPT;
 

diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 3215023..5d08ed9 100644 (file)
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -183,6 +183,7 @@ enum cpuhp_state {
        CPUHP_AP_PERF_POWERPC_THREAD_IMC_ONLINE,
        CPUHP_AP_PERF_POWERPC_TRACE_IMC_ONLINE,
        CPUHP_AP_PERF_POWERPC_HV_24x7_ONLINE,
+       CPUHP_AP_PERF_POWERPC_HV_GPCI_ONLINE,
        CPUHP_AP_WATCHDOG_ONLINE,
        CPUHP_AP_WORKQUEUE_ONLINE,
        CPUHP_AP_RCUTREE_ONLINE,