From aeeacd9d844b2219d47e9010298b635c68a2a4c9 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 23 May 2019 10:43:58 -0700 Subject: [PATCH] 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: Paul E. McKenney --- kernel/rcu/tree_plugin.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index ae927710d670..7077ef7bea96 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -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);