tracing/sched: Add trace events to track cpu hotplug.

Add ftrace event trace_sched_cpu_hotplug to track cpu
hot-add and hot-remove events.

This is useful in a variety of power, performance and
debug analysis scenarios.

Change-Id: I5d202c7a229ffacc3aafb7cf9afee0b0ee7b0931
Signed-off-by: Arun Bharadwaj <abharadw@codeaurora.org>
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 74e411a..3773129 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -24,6 +24,8 @@
 #include <linux/irq.h>
 #include <trace/events/power.h>
 
+#include <trace/events/sched.h>
+
 #include "smpboot.h"
 
 #ifdef CONFIG_SMP
@@ -425,6 +427,7 @@
 
 out_release:
 	cpu_hotplug_done();
+	trace_sched_cpu_hotplug(cpu, err, 0);
 	if (!err)
 		cpu_notify_nofail(CPU_POST_DEAD | mod, hcpu);
 	return err;
@@ -530,6 +533,7 @@
 		__cpu_notify(CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
 out:
 	cpu_hotplug_done();
+	trace_sched_cpu_hotplug(cpu, ret, 1);
 
 	return ret;
 }