netdev - [PATCH net-next 2/4] udp: relax atomic operation on sk->sk_rmem

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Date: Thu, 28 Mar 2024 14:40:30 +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: Willem de Bruijn <willemb@...gle.com>, netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 2/4] udp: relax atomic operation on sk->sk_rmem_alloc

atomic_add_return() is more expensive than atomic_add()
and seems overkill in UDP rx fast path.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/ipv4/udp.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index f2736e8958187e132ef45d8e25ab2b4ea7bcbc3d..d2fa9755727ce034c2b4bca82bd9e72130d588e6 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1516,12 +1516,7 @@ int __udp_enqueue_schedule_skb(struct sock *sk, struct sk_buff *skb)
 	size = skb->truesize;
 	udp_set_dev_scratch(skb);
 
-	/* we drop only if the receive buf is full and the receive
-	 * queue contains some other skb
-	 */
-	rmem = atomic_add_return(size, &sk->sk_rmem_alloc);
-	if (rmem > (size + (unsigned int)sk->sk_rcvbuf))
-		goto uncharge_drop;
+	atomic_add(size, &sk->sk_rmem_alloc);
 
 	spin_lock(&list->lock);
 	err = udp_rmem_schedule(sk, size);
-- 
2.44.0.396.g6e790dbe36-goog