From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Date: Tue, 29 Sep 2015 15:15:52 +0000 (-0700)
Subject: rcu: Short-circuit synchronize_sched_expedited() if only one CPU
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=06f60de19d3141f07d954c9275fe7ccca8e96b42;p=linux-beck.git

rcu: Short-circuit synchronize_sched_expedited() if only one CPU

If there is only one CPU, then invoking synchronize_sched_expedited()
is by definition a grace period.  This commit checks for this condition
and does a short-circuit return in that case.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 81aa1cdc6bc9..bd2605c144cc 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3822,6 +3822,10 @@ void synchronize_sched_expedited(void)
 	struct rcu_node *rnp;
 	struct rcu_state *rsp = &rcu_sched_state;
 
+	/* If only one CPU, this is automatically a grace period. */
+	if (rcu_blocking_is_gp())
+		return;
+
 	/* Take a snapshot of the sequence number.  */
 	s = rcu_exp_gp_seq_snap(rsp);