[PATCH tip/core/rcu 10/23] rcu: Allow RCU quiescent-state forcing to be preempted

From: Paul E. McKenney
Date: Thu Aug 30 2012 - 14:23:51 EST


From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>

RCU quiescent-state forcing is currently carried out without preemption
points, which can result in excessive latency spikes on large systems
(many hundreds or thousands of CPUs). This patch therefore inserts
a voluntary preemption point into force_qs_rnp(), which should greatly
reduce the magnitude of these spikes.

Reported-by: Mike Galbraith <mgalbraith@xxxxxxx>
Reported-by: Dimitri Sivanich <sivanich@xxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
kernel/rcutree.c | 1 +
1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 79c2c28..cce73ff 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1784,6 +1784,7 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
struct rcu_node *rnp;

rcu_for_each_leaf_node(rsp, rnp) {
+ cond_resched();
mask = 0;
raw_spin_lock_irqsave(&rnp->lock, flags);
if (!rcu_gp_in_progress(rsp)) {
--
1.7.8

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/