linux-kernel - [PATCH 3/8] refscale: Add local_bh

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Message-Id: <20251102224948.3906224-3-paulmck@kernel.org>
Date: Sun,  2 Nov 2025 14:49:43 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	kernel-team@...a.com,
	rostedt@...dmis.org,
	"Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH 3/8] refscale: Add local_bh_disable() readers

This commit adds refscale readers based on local_bh_disable() and
local_bh_enable() ("refscale.scale_type=bh").  On my x86 laptop, these
are about 4.9ns.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/refscale.c | 34 +++++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
index 266a3fa94b54..1faed90231ab 100644
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -636,6 +636,37 @@ static const struct ref_scale_ops jiffies_ops = {
 	.name		= "jiffies"
 };
 
+static void ref_bh_section(const int nloops)
+{
+	int i;
+
+	preempt_disable();
+	for (i = nloops; i >= 0; i--) {
+		local_bh_disable();
+		local_bh_enable();
+	}
+	preempt_enable();
+}
+
+static void ref_bh_delay_section(const int nloops, const int udl, const int ndl)
+{
+	int i;
+
+	preempt_disable();
+	for (i = nloops; i >= 0; i--) {
+		local_bh_disable();
+		un_delay(udl, ndl);
+		local_bh_enable();
+	}
+	preempt_enable();
+}
+
+static const struct ref_scale_ops bh_ops = {
+	.readsection	= ref_bh_section,
+	.delaysection	= ref_bh_delay_section,
+	.name		= "bh"
+};
+
 static void ref_irq_section(const int nloops)
 {
 	int i;
@@ -1236,7 +1267,8 @@ ref_scale_init(void)
 	static const struct ref_scale_ops *scale_ops[] = {
 		&rcu_ops, &srcu_ops, &srcu_fast_ops, RCU_TRACE_OPS RCU_TASKS_OPS
 		&refcnt_ops, &rwlock_ops, &rwsem_ops, &lock_ops, &lock_irq_ops,
-		&acqrel_ops, &sched_clock_ops, &clock_ops, &jiffies_ops, &irq_ops, &irqsave_ops,
+		&acqrel_ops, &sched_clock_ops, &clock_ops, &jiffies_ops,
+		&bh_ops, &irq_ops, &irqsave_ops,
 		&typesafe_ref_ops, &typesafe_lock_ops, &typesafe_seqlock_ops,
 	};
 
-- 
2.40.1