netdev - [PATCH net-next 09/10] udp: make busylock per socket

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Message-ID: <20250916160951.541279-10-edumazet@google.com>
Date: Tue, 16 Sep 2025 16:09:50 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, Willem de Bruijn <willemb@...gle.com>, 
	Kuniyuki Iwashima <kuniyu@...gle.com>, David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 09/10] udp: make busylock per socket

While having all spinlocks packed into an array was a space saver,
this also caused NUMA imbalance and hash collisions.

UDPv6 socket size becomes 1600 after this patch.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/linux/udp.h |  1 +
 include/net/udp.h   |  1 +
 net/ipv4/udp.c      | 20 ++------------------
 3 files changed, 4 insertions(+), 18 deletions(-)

diff --git a/include/linux/udp.h b/include/linux/udp.h
index 6ed008ab166557e868c1918daaaa5d551b7989a7..e554890c4415b411f35007d3ece9e6042db7a544 100644
--- a/include/linux/udp.h
+++ b/include/linux/udp.h
@@ -109,6 +109,7 @@ struct udp_sock {
 	 */
 	struct hlist_node	tunnel_list;
 	struct numa_drop_counters drop_counters;
+	spinlock_t		busylock ____cacheline_aligned_in_smp;
 };
 
 #define udp_test_bit(nr, sk)			\
diff --git a/include/net/udp.h b/include/net/udp.h
index a08822e294b038c0d00d4a5f5cac62286a207926..eecd64097f91196897f45530540b9c9b68c5ba4e 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -289,6 +289,7 @@ static inline void udp_lib_init_sock(struct sock *sk)
 	struct udp_sock *up = udp_sk(sk);
 
 	sk->sk_drop_counters = &up->drop_counters;
+	spin_lock_init(&up->busylock);
 	skb_queue_head_init(&up->reader_queue);
 	INIT_HLIST_NODE(&up->tunnel_list);
 	up->forward_threshold = sk->sk_rcvbuf >> 2;
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 25143f932447df2a84dd113ca33e1ccf15b3503c..7d1444821ee51a19cd5fd0dd5b8d096104c9283c 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1689,17 +1689,11 @@ static void udp_skb_dtor_locked(struct sock *sk, struct sk_buff *skb)
  * to relieve pressure on the receive_queue spinlock shared by consumer.
  * Under flood, this means that only one producer can be in line
  * trying to acquire the receive_queue spinlock.
- * These busylock can be allocated on a per cpu manner, instead of a
- * per socket one (that would consume a cache line per socket)
  */
-static int udp_busylocks_log __read_mostly;
-static spinlock_t *udp_busylocks __read_mostly;
-
-static spinlock_t *busylock_acquire(void *ptr)
+static spinlock_t *busylock_acquire(struct sock *sk)
 {
-	spinlock_t *busy;
+	spinlock_t *busy = &udp_sk(sk)->busylock;
 
-	busy = udp_busylocks + hash_ptr(ptr, udp_busylocks_log);
 	spin_lock(busy);
 	return busy;
 }
@@ -3997,7 +3991,6 @@ static void __init bpf_iter_register(void)
 void __init udp_init(void)
 {
 	unsigned long limit;
-	unsigned int i;
 
 	udp_table_init(&udp_table, "UDP");
 	limit = nr_free_buffer_pages() / 8;
@@ -4006,15 +3999,6 @@ void __init udp_init(void)
 	sysctl_udp_mem[1] = limit;
 	sysctl_udp_mem[2] = sysctl_udp_mem[0] * 2;
 
-	/* 16 spinlocks per cpu */
-	udp_busylocks_log = ilog2(nr_cpu_ids) + 4;
-	udp_busylocks = kmalloc(sizeof(spinlock_t) << udp_busylocks_log,
-				GFP_KERNEL);
-	if (!udp_busylocks)
-		panic("UDP: failed to alloc udp_busylocks\n");
-	for (i = 0; i < (1U << udp_busylocks_log); i++)
-		spin_lock_init(udp_busylocks + i);
-
 	if (register_pernet_subsys(&udp_sysctl_ops))
 		panic("UDP: failed to init sysctl parameters.\n");
 
-- 
2.51.0.384.g4c02a37b29-goog