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>
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 1ce887a..76c5c8b 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1107,6 +1107,8 @@
 				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);