Commit f48fe4c5 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu/nocb: Don't wake no-CBs GP kthread if timer posted under overload 



When under overload conditions, __call_rcu_nocb_wake() will wake the
no-CBs GP kthread any time the no-CBs CB kthread is asleep or there
are no ready-to-invoke callbacks, but only after a timer delay.  If the
no-CBs GP kthread has a ->nocb_bypass_timer pending, the deferred wakeup
from __call_rcu_nocb_wake() is redundant.  This commit therefore makes
__call_rcu_nocb_wake() avoid posting the redundant deferred wakeup if
->nocb_bypass_timer is pending.  This requires adding a bit of ordering
of timer actions.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.ibm.com>
parent 296181d7

kernel/rcu/tree_plugin.h

+5 −2
Original line number Diff line number Diff line
@@ -1909,8 +1909,10 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone, 
			rcu_advance_cbs_nowake(rdp->mynode, rdp);

			rdp->nocb_gp_adv_time = j;

		}

		if (rdp->nocb_cb_sleep ||

		    !rcu_segcblist_ready_cbs(&rdp->cblist))

		smp_mb(); /* Enqueue before timer_pending(). */

		if ((rdp->nocb_cb_sleep ||

		     !rcu_segcblist_ready_cbs(&rdp->cblist)) &&

		    !timer_pending(&rdp->nocb_bypass_timer))

			wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE,

					   TPS("WakeOvfIsDeferred"));

		rcu_nocb_unlock_irqrestore(rdp, flags);
@@ -1929,6 +1931,7 @@ static void do_nocb_bypass_wakeup_timer(struct timer_list *t) 


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

	rcu_nocb_lock_irqsave(rdp, flags);

	smp_mb__after_spinlock(); /* Timer expire before wakeup. */

	__call_rcu_nocb_wake(rdp, true, flags);

}

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