linux-kernel - [PATCH rcu 15/20] refscale: Add srcu_read_lock

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Message-Id: <20250224022214.12037-16-boqun.feng@gmail.com>
Date: Sun, 23 Feb 2025 18:22:09 -0800
From: Boqun Feng <boqun.feng@...il.com>
To: rcu@...r.kernel.org
Cc: Lai Jiangshan <jiangshanlai@...il.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Josh Triplett <josh@...htriplett.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Frederic Weisbecker <frederic@...nel.org>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	Joel Fernandes <joel@...lfernandes.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Uladzislau Rezki <urezki@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Shuah Khan <shuah@...nel.org>,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	bpf@...r.kernel.org,
	Alexei Starovoitov <ast@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Kent Overstreet <kent.overstreet@...ux.dev>
Subject: [PATCH rcu 15/20] refscale: Add srcu_read_lock_fast() support using "srcu-fast"

From: "Paul E. McKenney" <paulmck@...nel.org>

This commit creates a new srcu-fast option for the refscale.scale_type
module parameter that selects srcu_read_lock_fast() and
srcu_read_unlock_fast().

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Andrii Nakryiko <andrii@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: <bpf@...r.kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
---
 kernel/rcu/refscale.c | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
index 1b47376acdc4..f11a7c2af778 100644
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -216,6 +216,36 @@ static const struct ref_scale_ops srcu_ops = {
 	.name		= "srcu"
 };
 
+static void srcu_fast_ref_scale_read_section(const int nloops)
+{
+	int i;
+	struct srcu_ctr __percpu *scp;
+
+	for (i = nloops; i >= 0; i--) {
+		scp = srcu_read_lock_fast(srcu_ctlp);
+		srcu_read_unlock_fast(srcu_ctlp, scp);
+	}
+}
+
+static void srcu_fast_ref_scale_delay_section(const int nloops, const int udl, const int ndl)
+{
+	int i;
+	struct srcu_ctr __percpu *scp;
+
+	for (i = nloops; i >= 0; i--) {
+		scp = srcu_read_lock_fast(srcu_ctlp);
+		un_delay(udl, ndl);
+		srcu_read_unlock_fast(srcu_ctlp, scp);
+	}
+}
+
+static const struct ref_scale_ops srcu_fast_ops = {
+	.init		= rcu_sync_scale_init,
+	.readsection	= srcu_fast_ref_scale_read_section,
+	.delaysection	= srcu_fast_ref_scale_delay_section,
+	.name		= "srcu-fast"
+};
+
 static void srcu_lite_ref_scale_read_section(const int nloops)
 {
 	int i;
@@ -1163,7 +1193,7 @@ ref_scale_init(void)
 	long i;
 	int firsterr = 0;
 	static const struct ref_scale_ops *scale_ops[] = {
-		&rcu_ops, &srcu_ops, &srcu_lite_ops, RCU_TRACE_OPS RCU_TASKS_OPS
+		&rcu_ops, &srcu_ops, &srcu_fast_ops, &srcu_lite_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,
 		&typesafe_ref_ops, &typesafe_lock_ops, &typesafe_seqlock_ops,
-- 
2.39.5 (Apple Git-154)