[PATCH tip/core/rcu 01/11] rcu: Expedite grace periods during suspend/resume

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

From: Borislav Petkov <bp@alien8.de>

CONFIG_RCU_FAST_NO_HZ can increase grace-period durations by up to
a factor of four, which can result in long suspend and resume times.
Thus, this commit temporarily switches to expedited grace periods when
suspending the box and return to normal settings when resuming.

[ paulmck: This also papers over an audio/irq bug, but hopefully that will
  be fixed soon. ]

Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcutree.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 338f1d1..69e4792 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -54,6 +54,7 @@
 #include <linux/stop_machine.h>
 #include <linux/random.h>
 #include <linux/ftrace_event.h>
+#include <linux/suspend.h>
 
 #include "rcutree.h"
 #include <trace/events/rcu.h>
@@ -3032,6 +3033,22 @@ static int rcu_cpu_notify(struct notifier_block *self,
 	return NOTIFY_OK;
 }
 
+static int rcu_pm_notify(struct notifier_block *self,
+			 unsigned long action, void *hcpu)
+{
+	switch (action) {
+	case PM_HIBERNATION_PREPARE:
+		rcu_expedited = 1;
+		break;
+	case PM_POST_RESTORE:
+		rcu_expedited = 0;
+		break;
+	default:
+		break;
+	}
+	return NOTIFY_OK;
+}
+
 /*
  * Spawn the kthread that handles this RCU flavor's grace periods.
  */
@@ -3273,6 +3290,7 @@ void __init rcu_init(void)
 	 * or the scheduler are operational.
 	 */
 	cpu_notifier(rcu_cpu_notify, 0);
+	pm_notifier(rcu_pm_notify, 0);
 	for_each_online_cpu(cpu)
 		rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
 }
-- 
1.8.1.5