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Commit 06ae115a authored by Paul E. McKenney's avatar Paul E. McKenney
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rcu: Avoid having just-onlined CPU resched itself when RCU is idle 



CPUs set rdp->qs_pending when coming online to resolve races with
grace-period start.  However, this means that if RCU is idle, the
just-onlined CPU might needlessly send itself resched IPIs.  Adjust
the online-CPU initialization to avoid this, and also to correctly
cause the CPU to respond to the current grace period if needed.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: default avatarJosh Boyer <jwboyer@redhat.com>
Tested-by: default avatarChristian Hoffmann <email@christianhoffmann.info>
parent 9bc8b558

kernel/rcutree.c

+8 −3
Original line number Diff line number Diff line
@@ -1911,8 +1911,6 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible) 


	/* Set up local state, ensuring consistent view of global state. */

	raw_spin_lock_irqsave(&rnp->lock, flags);

	rdp->passed_quiesce = 0;  /* We could be racing with new GP, */

	rdp->qs_pending = 1;	 /*  so set up to respond to current GP. */

	rdp->beenonline = 1;	 /* We have now been online. */

	rdp->preemptible = preemptible;

	rdp->qlen_last_fqs_check = 0;
@@ -1937,8 +1935,15 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible) 
		rnp->qsmaskinit |= mask;

		mask = rnp->grpmask;

		if (rnp == rdp->mynode) {

			rdp->gpnum = rnp->completed; /* if GP in progress... */

			/*

			 * If there is a grace period in progress, we will

			 * set up to wait for it next time we run the

			 * RCU core code.

			 */

			rdp->gpnum = rnp->completed;

			rdp->completed = rnp->completed;

			rdp->passed_quiesce = 0;

			rdp->qs_pending = 0;

			rdp->passed_quiesce_gpnum = rnp->gpnum - 1;

			trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpuonl");

		}