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>

include/trace/events/sched.h

@@ -191,6 +191,31 @@ TRACE_EVENT(sched_migrate_task,
 		  __entry->orig_cpu, __entry->dest_cpu)
 );
 
+/*
+ * Tracepoint for a CPU going offline/online:
+ */
+TRACE_EVENT(sched_cpu_hotplug,
+
+	TP_PROTO(int affected_cpu, int error, int status),
+
+	TP_ARGS(affected_cpu, error, status),
+
+	TP_STRUCT__entry(
+		__field(	int,	affected_cpu		)
+		__field(	int,	error			)
+		__field(	int,	status			)
+	),
+
+	TP_fast_assign(
+		__entry->affected_cpu	= affected_cpu;
+		__entry->error		= error;
+		__entry->status		= status;
+	),
+
+	TP_printk("cpu %d %s error=%d", __entry->affected_cpu,
+		__entry->status ? "online" : "offline", __entry->error)
+);
+
 DECLARE_EVENT_CLASS(sched_process_template,
 
 	TP_PROTO(struct task_struct *p),

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 @@ static int _cpu_down(unsigned int cpu, int tasks_frozen)
 
 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 @@ out_notify:
 		__cpu_notify(CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
 out:
 	cpu_hotplug_done();
+	trace_sched_cpu_hotplug(cpu, ret, 1);
 
 	return ret;
 }