rcu/nocb: Avoid synchronous wakeup in __call_rcu_nocb_wake() (273f0340) · Commits · 戴 / test

When callbacks are in full flow, the common case is waiting for a grace period, and this grace period will normally take a few jiffies to complete. It therefore isn't all that helpful for __call_rcu_nocb_wake() to do a synchronous wakeup in this case. This commit therefore turns this into a timer-based deferred wakeup of the no-CBs grace-period kthread. Signed-off-by:

Paul E. McKenney <paulmck@linux.ibm.com>

kernel/rcu/tree_plugin.h

+5 −14

Original line number	Diff line number	Diff line
		@@ -1900,22 +1900,13 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
		} else if (len > rdp->qlen_last_fqs_check + qhimark) {
		/* ... or if many callbacks queued. */
		rdp->qlen_last_fqs_check = len;
		if (!rdp->nocb_cb_sleep &&
		rcu_segcblist_ready_cbs(&rdp->cblist)) {
		// Already going full tilt, so don't try to rewake.
		rcu_nocb_unlock_irqrestore(rdp, flags);
		} else {
		if (rdp->nocb_cb_sleep \|\|
		!rcu_segcblist_ready_cbs(&rdp->cblist)) {
		rcu_advance_cbs_nowake(rdp->mynode, rdp);
		if (!irqs_disabled_flags(flags)) {
		wake_nocb_gp(rdp, false, flags);
		trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
		TPS("WakeOvf"));
		} else {
		wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE,
		TPS("WakeOvfIsDeferred"));
		rcu_nocb_unlock_irqrestore(rdp, flags);
		}
		}
		rcu_nocb_unlock_irqrestore(rdp, flags);
		} else {
		trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
		rcu_nocb_unlock_irqrestore(rdp, flags);

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