Commit aeeacd9d authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu/nocb: Enable re-awakening under high callback load 



The __call_rcu_nocb_wake() function and its predecessors set
->qlen_last_fqs_check to zero for the first callback and to LONG_MAX / 2
for forced reawakenings.  The former can result in a too-quick reawakening
when there are many callbacks ready to invoke and the latter prevents a
second reawakening.  This commit therefore sets ->qlen_last_fqs_check
to the current number of callbacks in both cases.  While in the area,
this commit also moves both assignments under ->nocb_lock.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.ibm.com>
parent 0bd55c69

kernel/rcu/tree_plugin.h

+2 −2
Original line number Diff line number Diff line
@@ -1628,6 +1628,7 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone, 
	// Need to actually to a wakeup.

	len = rcu_segcblist_n_cbs(&rdp->cblist);

	if (was_alldone) {

		rdp->qlen_last_fqs_check = len;

		if (!irqs_disabled_flags(flags)) {

			/* ... if queue was empty ... */

			wake_nocb_gp(rdp, false, flags);
@@ -1638,9 +1639,9 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone, 
					   TPS("WakeEmptyIsDeferred"));

			rcu_nocb_unlock_irqrestore(rdp, flags);

		}

		rdp->qlen_last_fqs_check = 0;

	} else if (len > rdp->qlen_last_fqs_check + qhimark) {

		/* ... or if many callbacks queued. */

		rdp->qlen_last_fqs_check = len;

		if (!irqs_disabled_flags(flags)) {

			wake_nocb_gp(rdp, true, flags);

			trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
@@ -1650,7 +1651,6 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone, 
					   TPS("WakeOvfIsDeferred"));

			rcu_nocb_unlock_irqrestore(rdp, flags);

		}

		rdp->qlen_last_fqs_check = LONG_MAX / 2;

	} else {

		trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));

		rcu_nocb_unlock_irqrestore(rdp, flags);

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