linux-kernel - [PATCH tip/core/rcu 02/11] rcu: Expedite during suspend and resume only on smallish systems

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Date:	Sat, 17 Aug 2013 18:37:47 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com,
	edumazet@...gle.com, darren@...art.com, fweisbec@...il.com,
	sbw@....edu, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 02/11] rcu: Expedite during suspend and resume only on smallish systems

From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>

Expedited grace periods are of dubious benefit on very large systems,
so this commit restricts their automated use during suspend and resume
to systems of 256 or fewer CPUs.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcutree.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 69e4792..6ec33dc 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -3038,7 +3038,8 @@ static int rcu_pm_notify(struct notifier_block *self,
 {
 	switch (action) {
 	case PM_HIBERNATION_PREPARE:
-		rcu_expedited = 1;
+		if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
+			rcu_expedited = 1;
 		break;
 	case PM_POST_RESTORE:
 		rcu_expedited = 0;
-- 
1.8.1.5

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