Commit d25eb944 authored Mar 18, 2010 by Paul E. McKenney

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>

parent 2b3fc35f

kernel/rcutree.c

+10 −0

Original line number	Diff line number	Diff line
		@@ -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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