linux-kernel - [PATCH tip/core/rcu 01/18] rcu: Unconditionally expedite during suspend/hibernate

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Message-Id: <20190326231314.19518-1-paulmck@linux.ibm.com>
Date:   Tue, 26 Mar 2019 16:12:57 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>
Subject: [PATCH tip/core/rcu 01/18] rcu: Unconditionally expedite during suspend/hibernate

The rcu_pm_notify() function refuses to switch to/from expedited grace
periods on systems with more than 256 CPUs due to the serialized
initialization of expedited grace periods.  However, expedited grace
periods are now initialized in parallel, removing this concern.
This commit therefore removes the checks from rcu_pm_notify(), so that
expedited grace periods are used unconditionally during suspend/resume
and hibernate/wake operations.

As always, real-time workloads wishing to completely avoid expedited
grace periods can use the rcupdate.rcu_normal= kernel parameter.

Signed-off-by: Paul E. McKenney <paulmck@...ux.ibm.com>
---
 kernel/rcu/tree.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index acd6ccf56faf..95e3250b7b6e 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3559,13 +3559,11 @@ static int rcu_pm_notify(struct notifier_block *self,
 	switch (action) {
 	case PM_HIBERNATION_PREPARE:
 	case PM_SUSPEND_PREPARE:
-		if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
-			rcu_expedite_gp();
+		rcu_expedite_gp();
 		break;
 	case PM_POST_HIBERNATION:
 	case PM_POST_SUSPEND:
-		if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
-			rcu_unexpedite_gp();
+		rcu_unexpedite_gp();
 		break;
 	default:
 		break;
-- 
2.17.1