perf: Introduce perf_pmu_migrate_context()

Originally from Peter Zijlstra. The helper migrates perf events
from one cpu to another cpu.
Signed-off-by: Zheng Yan <zheng.z.yan@intel.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1339741902-8449-5-git-send-email-zheng.z.yan@intel.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/perf_event.h

@@ -1107,6 +1107,8 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr,
 				struct task_struct *task,
 				perf_overflow_handler_t callback,
 				void *context);
+extern void perf_pmu_migrate_context(struct pmu *pmu,
+				int src_cpu, int dst_cpu);
 extern u64 perf_event_read_value(struct perf_event *event,
 				 u64 *enabled, u64 *running);
 

kernel/events/core.c

@@ -1645,6 +1645,8 @@ perf_install_in_context(struct perf_event_context *ctx,
 	lockdep_assert_held(&ctx->mutex);
 
 	event->ctx = ctx;
+	if (event->cpu != -1)
+		event->cpu = cpu;
 
 	if (!task) {
 		/*
@@ -6379,6 +6381,7 @@ SYSCALL_DEFINE5(perf_event_open,
 	mutex_lock(&ctx->mutex);
 
 	if (move_group) {
+		synchronize_rcu();
 		perf_install_in_context(ctx, group_leader, event->cpu);
 		get_ctx(ctx);
 		list_for_each_entry(sibling, &group_leader->sibling_list,
@@ -6484,6 +6487,39 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,
 }
 EXPORT_SYMBOL_GPL(perf_event_create_kernel_counter);
 
+void perf_pmu_migrate_context(struct pmu *pmu, int src_cpu, int dst_cpu)
+{
+	struct perf_event_context *src_ctx;
+	struct perf_event_context *dst_ctx;
+	struct perf_event *event, *tmp;
+	LIST_HEAD(events);
+
+	src_ctx = &per_cpu_ptr(pmu->pmu_cpu_context, src_cpu)->ctx;
+	dst_ctx = &per_cpu_ptr(pmu->pmu_cpu_context, dst_cpu)->ctx;
+
+	mutex_lock(&src_ctx->mutex);
+	list_for_each_entry_safe(event, tmp, &src_ctx->event_list,
+				 event_entry) {
+		perf_remove_from_context(event);
+		put_ctx(src_ctx);
+		list_add(&event->event_entry, &events);
+	}
+	mutex_unlock(&src_ctx->mutex);
+
+	synchronize_rcu();
+
+	mutex_lock(&dst_ctx->mutex);
+	list_for_each_entry_safe(event, tmp, &events, event_entry) {
+		list_del(&event->event_entry);
+		if (event->state >= PERF_EVENT_STATE_OFF)
+			event->state = PERF_EVENT_STATE_INACTIVE;
+		perf_install_in_context(dst_ctx, event, dst_cpu);
+		get_ctx(dst_ctx);
+	}
+	mutex_unlock(&dst_ctx->mutex);
+}
+EXPORT_SYMBOL_GPL(perf_pmu_migrate_context);
+
 static void sync_child_event(struct perf_event *child_event,
 			       struct task_struct *child)
 {