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Subject[PATCH tip/core/rcu 10/23] rcu: Allow RCU quiescent-state forcing to be preempted
Date
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

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@suse.de>
Reported-by: Dimitri Sivanich <sivanich@sgi.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
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


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