[PATCH V4 2/2] tracing, perf : add cpu hotplug trace events

[Vincent Guittot]

Please find below a new proposal for adding trace events for cpu hotplug.
The goal is to measure the latency of each part (kernel, architecture)
and also to trace the cpu hotplug activity with other power events. I
have tested these traces events on an arm platform.

Subject: [PATCH 2/2] add hotplug tracepoint

this patch adds new events for cpu hotplug tracing
 * plug/unplug sequence
 * core and architecture latency measurements

Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
---
 kernel/cpu.c |   18 ++++++++++++++++++
 1 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 156cc55..692e819 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -16,6 +16,9 @@
 #include <linux/mutex.h>
 #include <linux/gfp.h>

+#define CREATE_TRACE_POINTS
+#include <trace/events/cpu_hotplug.h>
+
 #ifdef CONFIG_SMP
 /* Serializes the updates to cpu_online_mask, cpu_present_mask */
 static DEFINE_MUTEX(cpu_add_remove_lock);
@@ -197,10 +200,13 @@ struct take_cpu_down_param {
 static int __ref take_cpu_down(void *_param)
 {
 	struct take_cpu_down_param *param = _param;
+	unsigned int cpu = (unsigned int)(param->hcpu);
 	int err;

 	/* Ensure this CPU doesn't handle any more interrupts. */
+	trace_cpu_hotplug_disable_start(cpu);
 	err = __cpu_disable();
+	trace_cpu_hotplug_disable_end(cpu);
 	if (err < 0)
 		return err;

@@ -256,7 +262,9 @@ static int __ref _cpu_down(unsigned int cpu, int
tasks_frozen)
 		cpu_relax();

 	/* This actually kills the CPU. */
+	trace_cpu_hotplug_die_start(cpu);
 	__cpu_die(cpu);
+	trace_cpu_hotplug_die_end(cpu);

 	/* CPU is completely dead: tell everyone.  Too late to complain. */
 	cpu_notify_nofail(CPU_DEAD | mod, hcpu);
@@ -274,6 +282,8 @@ int __ref cpu_down(unsigned int cpu)
 {
 	int err;

+	trace_cpu_hotplug_down_start(cpu);
+
 	cpu_maps_update_begin();

 	if (cpu_hotplug_disabled) {
@@ -285,6 +295,8 @@ int __ref cpu_down(unsigned int cpu)

 out:
 	cpu_maps_update_done();
+
+	trace_cpu_hotplug_down_end(cpu);
 	return err;
 }
 EXPORT_SYMBOL(cpu_down);
@@ -310,7 +322,9 @@ static int __cpuinit _cpu_up(unsigned int cpu, int
tasks_frozen)
 	}

 	/* Arch-specific enabling code. */
+	trace_cpu_hotplug_arch_up_start(cpu);
 	ret = __cpu_up(cpu);
+	trace_cpu_hotplug_arch_up_end(cpu);
 	if (ret != 0)
 		goto out_notify;
 	BUG_ON(!cpu_online(cpu));
@@ -335,6 +349,8 @@ int __cpuinit cpu_up(unsigned int cpu)
 	pg_data_t	*pgdat;
 #endif

+	trace_cpu_hotplug_up_start(cpu);
+
 	if (!cpu_possible(cpu)) {
 		printk(KERN_ERR "can't online cpu %d because it is not "
 			"configured as may-hotadd at boot time\n", cpu);
@@ -376,6 +392,8 @@ int __cpuinit cpu_up(unsigned int cpu)

 	err = _cpu_up(cpu, 0);

+	trace_cpu_hotplug_up_end(cpu);
+
 out:
 	cpu_maps_update_done();
 	return err;
-- 
1.7.1
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