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.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 36 insertions, 0 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index fa36a39e8bb7..f1cf0edeb39a 100644
--- a/kernel/events/core.c
+++ b/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 @@ err:
 }
 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)
 {