[PATCH] a patch to fix the cpu-offline-online problem caused by pm_idle

[Luming Yu]

Hi there,

I've seen many problems caused by deep-c-state-capable pm_idle on a
NHM-EX system with this test script
# for i in `seq 1 1000`; do echo $i; echo 0 >
/sys/devices/system/cpu/cpu59/online ; sleep 1; echo 1 >
/sys/devices/system/cpu/cpu59/online; done

As the bug " CPU online/offline causes system slowdown"
https://bugzilla.redhat.com/show_bug.cgi?id=586551 described.

The simplest and easiest and cleanest way I can think of now is as the
patch attached.

Signed-off-by: Yu Luming <luming.yu@xxxxxxxxx>

diff --git a/kernel/cpu.c b/kernel/cpu.c
index c75fcdd..d419eb3 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -135,6 +135,7 @@ int __ref register_cpu_notifier(struct notifier_block *nb)

 #ifdef CONFIG_HOTPLUG_CPU

+static void (*pm_idle_saved) (void) __read_mostly;
 EXPORT_SYMBOL(register_cpu_notifier);

 void __ref unregister_cpu_notifier(struct notifier_block *nb)
@@ -145,6 +146,19 @@ void __ref unregister_cpu_notifier(struct
notifier_block *nb)
 }
 EXPORT_SYMBOL(unregister_cpu_notifier);

+static inline void save_pm_idle(void)
+{
+	pm_idle_saved = pm_idle;
+	pm_idle = default_idle;
+	cpu_idle_wait();
+}
+
+static inline void restore_pm_idle(void)
+{
+	pm_idle = pm_idle_saved;
+	cpu_idle_wait();
+}
+
 static inline void check_for_tasks(int cpu)
 {
 	struct task_struct *p;
@@ -278,7 +292,9 @@ int __ref cpu_down(unsigned int cpu)
 		goto out;
 	}

+	save_pm_idle();
 	err = _cpu_down(cpu, 0);
+	restore_pm_idle();

 out:
 	cpu_maps_update_done();
@@ -376,7 +392,9 @@ int __cpuinit cpu_up(unsigned int cpu)
 		goto out;
 	}

+	save_pm_idle();
 	err = _cpu_up(cpu, 0);
+	restore_pm_idle();

 out:
 	cpu_maps_update_done();

Attachment: bz586551-using-default-idle.patch
Description: Binary data