linux-kernel - [PATCH tip/core/rcu 12/18] rcu: Default jiffies_to_sched_qs to jiffies_till_sched

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Date:   Tue, 26 Mar 2019 16:13:08 -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,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        "Paul E . McKenney" <paulmck@...ux.ibm.com>
Subject: [PATCH tip/core/rcu 12/18] rcu: Default jiffies_to_sched_qs to jiffies_till_sched_qs

From: Neeraj Upadhyay <neeraju@...eaurora.org>

The current code only calls adjust_jiffies_till_sched_qs() if
jiffies_till_sched_qs is left at its default value, so when the
jiffies_till_sched_qs kernel-boot parameter actually is specified,
jiffies_to_sched_qs will be left with the value zero, which
will result in useless slowdowns of cond_resched().  This commit
therefore changes rcu_init_geometry() to unconditionally invoke
adjust_jiffies_till_sched_qs(), which ensures that jiffies_to_sched_qs
will be initialized in all cases, thus maintaining good cond_resched()
performance.

Signed-off-by: Neeraj Upadhyay <neeraju@...eaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.ibm.com>
---
 kernel/rcu/tree.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 139fa1f5c537..466299c3d2da 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3739,8 +3739,7 @@ static void __init rcu_init_geometry(void)
 		jiffies_till_first_fqs = d;
 	if (jiffies_till_next_fqs == ULONG_MAX)
 		jiffies_till_next_fqs = d;
-	if (jiffies_till_sched_qs == ULONG_MAX)
-		adjust_jiffies_till_sched_qs();
+	adjust_jiffies_till_sched_qs();
 
 	/* If the compile-time values are accurate, just leave. */
 	if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
-- 
2.17.1