Commit-ID: d25eb9442bb2c38c1e742f0fa764d7132d72593f
Gitweb: http://git.kernel.org/tip/d25eb9442bb2c38c1e742f0fa764d7132d72593f
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Thu, 18 Mar 2010 21:36:51 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Mon, 10 May 2010 11:08:31 -0700
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@xxxxxxxxxxxxxxxxxx>
---
kernel/rcutree.c | 10 ++++++++++
1 files changed, 10 insertions(+), 0 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 3ec8160..e54c123 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;
}
--
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