linux-kernel - [tip:core/rcu] rcu: Fix holdoff for accelerated GPs for last non-dynticked CPU

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Date:	Sun, 28 Feb 2010 08:59:01 GMT
From:	"tip-bot for Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	hpa@...or.com, mingo@...hat.com, tglx@...utronix.de, mingo@...e.hu
Subject: [tip:core/rcu] rcu: Fix holdoff for accelerated GPs for last non-dynticked CPU

Commit-ID:  622ea685f1fafdf84d612440535c84341f0860b8
Gitweb:     http://git.kernel.org/tip/622ea685f1fafdf84d612440535c84341f0860b8
Author:     Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
AuthorDate: Sat, 27 Feb 2010 14:53:07 -0800
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Sun, 28 Feb 2010 09:17:42 +0100

rcu: Fix holdoff for accelerated GPs for last non-dynticked CPU

Make the holdoff only happen when the full number of attempts
have been made.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: laijs@...fujitsu.com
Cc: dipankar@...ibm.com
Cc: mathieu.desnoyers@...ymtl.ca
Cc: josh@...htriplett.org
Cc: dvhltc@...ibm.com
Cc: niv@...ibm.com
Cc: peterz@...radead.org
Cc: rostedt@...dmis.org
Cc: Valdis.Kletnieks@...edu
Cc: dhowells@...hat.com
LKML-Reference: <1267311188-16603-1-git-send-email-paulmck@...ux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/rcutree_plugin.h |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 464ad2c..79b53bd 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1010,6 +1010,10 @@ int rcu_needs_cpu(int cpu)
 	int c = 0;
 	int thatcpu;
 
+	/* Check for being in the holdoff period. */
+	if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies)
+		return rcu_needs_cpu_quick_check(cpu);
+
 	/* Don't bother unless we are the last non-dyntick-idle CPU. */
 	for_each_cpu_not(thatcpu, nohz_cpu_mask)
 		if (thatcpu != cpu) {
@@ -1041,10 +1045,8 @@ int rcu_needs_cpu(int cpu)
 	}
 
 	/* If RCU callbacks are still pending, RCU still needs this CPU. */
-	if (c) {
+	if (c)
 		raise_softirq(RCU_SOFTIRQ);
-		per_cpu(rcu_dyntick_holdoff, cpu) = jiffies;
-	}
 	return c;
 }
 
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