Add cpu hotplug support for perf counters

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/ltt-context.c b/ltt-context.c
index 8f00bb1bd0067437170efa7aaecd23df8768212e..634694b968d4c06f6cf5066b684c80efc10d68d9 100644 (file)
--- a/ltt-context.c
+++ b/ltt-context.c
@@ -45,6 +45,17 @@ struct lttng_ctx_field *lttng_append_context(struct lttng_ctx **ctx_p)
 }
 EXPORT_SYMBOL_GPL(lttng_append_context);
 
+void lttng_remove_context_field(struct lttng_ctx **ctx_p,
+                               struct lttng_ctx_field *field)
+{
+       struct lttng_ctx *ctx;
+
+       ctx = *ctx_p;
+       ctx->nr_fields--;
+       memset(&ctx->fields[ctx->nr_fields], 0, sizeof(struct lttng_ctx_field));
+}
+EXPORT_SYMBOL_GPL(lttng_remove_context_field);
+
 void lttng_destroy_context(struct lttng_ctx *ctx)
 {
        int i;

diff --git a/ltt-events.h b/ltt-events.h
index 6244e8c5a49df5427226f8d9d8163a9a237d5337..ec70eceadc69986627e2b02031a3b41324185c86 100644 (file)
--- a/ltt-events.h
+++ b/ltt-events.h
@@ -128,7 +128,8 @@ struct lttng_ctx_field {
        union {
                struct {
                        struct perf_event **e;  /* per-cpu array */
-                       struct list_head head;
+                       struct notifier_block nb;
+                       int hp_enable;
                        struct perf_event_attr *attr;
                } perf_counter;
        } u;
@@ -273,6 +274,8 @@ void ltt_event_put(const struct lttng_event_desc *desc);
 int ltt_probes_init(void);
 void ltt_probes_exit(void);
 struct lttng_ctx_field *lttng_append_context(struct lttng_ctx **ctx);
+void lttng_remove_context_field(struct lttng_ctx **ctx,
+                               struct lttng_ctx_field *field);
 void lttng_destroy_context(struct lttng_ctx *ctx);
 int lttng_add_pid_to_ctx(struct lttng_ctx **ctx);
 int lttng_add_comm_to_ctx(struct lttng_ctx **ctx);

diff --git a/lttng-context-perf-counters.c b/lttng-context-perf-counters.c
index 20d49d580760b8c4ed8cd15ce239bb6c2d77b17b..2e194991daf79f24d4bb9f255e99f7f1919cf2d5 100644 (file)
--- a/lttng-context-perf-counters.c
+++ b/lttng-context-perf-counters.c
@@ -17,13 +17,6 @@
 #include "wrapper/vmalloc.h"
 #include "ltt-tracer.h"
 
-/*
- * TODO: Add CPU hotplug support.
- */
-
-static DEFINE_MUTEX(perf_counter_mutex);
-static LIST_HEAD(perf_counter_contexts);
-
 static
 size_t perf_counter_get_size(size_t offset)
 {
@@ -62,16 +55,66 @@ void lttng_destroy_perf_counter_field(struct lttng_ctx_field *field)
        struct perf_event **events = field->u.perf_counter.e;
        int cpu;
 
-       mutex_lock(&perf_counter_mutex);
-       list_del(&field->u.perf_counter.head);
+       get_online_cpus();
        for_each_online_cpu(cpu)
                perf_event_release_kernel(events[cpu]);
-       mutex_unlock(&perf_counter_mutex);
+       put_online_cpus();
+#ifdef CONFIG_HOTPLUG_CPU
+       unregister_cpu_notifier(&field->u.perf_counter.nb);
+#endif
        kfree(field->event_field.name);
        kfree(field->u.perf_counter.attr);
        kfree(events);
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+
+/**
+ *     lttng_perf_counter_hp_callback - CPU hotplug callback
+ *     @nb: notifier block
+ *     @action: hotplug action to take
+ *     @hcpu: CPU number
+ *
+ *     Returns the success/failure of the operation. (%NOTIFY_OK, %NOTIFY_BAD)
+ *
+ * We can setup perf counters when the cpu is online (up prepare seems to be too
+ * soon).
+ */
+static
+int __cpuinit lttng_perf_counter_cpu_hp_callback(struct notifier_block *nb,
+                                                unsigned long action,
+                                                void *hcpu)
+{
+       unsigned int cpu = (unsigned long) hcpu;
+       struct lttng_ctx_field *field =
+               container_of(nb, struct lttng_ctx_field, u.perf_counter.nb);
+       struct perf_event **events = field->u.perf_counter.e;
+       struct perf_event_attr *attr = field->u.perf_counter.attr;
+       
+
+       if (!field->u.perf_counter.hp_enable)
+               return NOTIFY_OK;
+
+       switch (action) {
+       case CPU_ONLINE:
+       case CPU_ONLINE_FROZEN:
+               events[cpu] = perf_event_create_kernel_counter(attr,
+                               cpu, NULL, overflow_callback);
+               if (!events[cpu])
+                       return NOTIFY_BAD;
+               break;
+       case CPU_UP_CANCELED:
+       case CPU_UP_CANCELED_FROZEN:
+       case CPU_DEAD:
+       case CPU_DEAD_FROZEN:
+               perf_event_release_kernel(events[cpu]);
+               break;
+       }
+       return NOTIFY_OK;
+}
+
+#endif
+
 int lttng_add_perf_counter_to_ctx(uint32_t type,
                                  uint64_t config,
                                  const char *name,
@@ -100,17 +143,6 @@ int lttng_add_perf_counter_to_ctx(uint32_t type,
        attr->pinned = 1;
        attr->disabled = 0;
 
-       mutex_lock(&perf_counter_mutex);
-
-       for_each_online_cpu(cpu) {
-               events[cpu] = perf_event_create_kernel_counter(attr,
-                                       cpu, NULL, overflow_callback);
-               if (!events[cpu]) {
-                       ret = -EINVAL;
-                       goto name_alloc_error;
-               }
-       }
-
        name_alloc = kstrdup(name, GFP_KERNEL);
        if (!name_alloc) {
                ret = -ENOMEM;
@@ -120,8 +152,27 @@ int lttng_add_perf_counter_to_ctx(uint32_t type,
        field = lttng_append_context(ctx);
        if (!field) {
                ret = -ENOMEM;
-               goto error;
+               goto append_context_error;
        }
+
+#ifdef CONFIG_HOTPLUG_CPU
+       field->u.perf_counter.nb.notifier_call =
+               lttng_perf_counter_cpu_hp_callback;
+       field->u.perf_counter.nb.priority = 0;
+       register_cpu_notifier(&field->u.perf_counter.nb);
+#endif
+
+       get_online_cpus();
+       for_each_online_cpu(cpu) {
+               events[cpu] = perf_event_create_kernel_counter(attr,
+                                       cpu, NULL, overflow_callback);
+               if (!events[cpu]) {
+                       ret = -EINVAL;
+                       goto counter_error;
+               }
+       }
+       put_online_cpus();
+
        field->destroy = lttng_destroy_perf_counter_field;
 
        field->event_field.name = name_alloc;
@@ -136,21 +187,24 @@ int lttng_add_perf_counter_to_ctx(uint32_t type,
        field->record = perf_counter_record;
        field->u.perf_counter.e = events;
        field->u.perf_counter.attr = attr;
-
-       list_add(&field->u.perf_counter.head, &perf_counter_contexts);
-       mutex_unlock(&perf_counter_mutex);
+       field->u.perf_counter.hp_enable = 1;
 
        wrapper_vmalloc_sync_all();
        return 0;
 
-error:
-       kfree(name_alloc);
-name_alloc_error:
+counter_error:
        for_each_online_cpu(cpu) {
                if (events[cpu])
                        perf_event_release_kernel(events[cpu]);
        }
-       mutex_unlock(&perf_counter_mutex);
+       put_online_cpus();
+#ifdef CONFIG_HOTPLUG_CPU
+       unregister_cpu_notifier(&field->u.perf_counter.nb);
+#endif
+       lttng_remove_context_field(ctx, field);
+append_context_error:
+       kfree(name_alloc);
+name_alloc_error:
        kfree(attr);
 error_attr:
        kfree(events);