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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-03-18 21:36:51 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-05-10 11:08:31 -0700
commitd25eb9442bb2c38c1e742f0fa764d7132d72593f (patch)
tree0a2604a3b61ce7a0868c021ac945d9826e0d88f1
parent2b3fc35f6919344e3cf722dde8308f47235c0b70 (diff)
downloadlinux-2.6.34-ux500-d25eb9442bb2c38c1e742f0fa764d7132d72593f.tar.gz
rcu: substitute set_need_resched for sending resched IPIs
This patch adds a check to __rcu_pending() that does a local set_need_resched() if the current CPU is holding up the current grace period and if force_quiescent_state() will be called soon. The goal is to reduce the probability that force_quiescent_state() will need to do smp_send_reschedule(), which sends an IPI and is therefore more expensive on most architectures. Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
-rw-r--r--kernel/rcutree.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 3ec8160fc75..e54c1235122 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1499,6 +1499,16 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
/* Is the RCU core waiting for a quiescent state from this CPU? */
if (rdp->qs_pending) {
+
+ /*
+ * If force_quiescent_state() coming soon and this CPU
+ * needs a quiescent state, and this is either RCU-sched
+ * or RCU-bh, force a local reschedule.
+ */
+ if (!rdp->preemptable &&
+ ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs) - 1,
+ jiffies))
+ set_need_resched();
rdp->n_rp_qs_pending++;
return 1;
}