netdev - Re: [PATCH net-next 10/10] udp: use skb_attempt_defer

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Message-ID: <513d3647-55a8-45ed-8c61-b7bf61eec9f4@redhat.com>
Date: Wed, 17 Sep 2025 18:15:29 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Eric Dumazet <edumazet@...gle.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,
 "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH net-next 10/10] udp: use skb_attempt_defer_free()

On 9/16/25 6:09 PM, Eric Dumazet wrote:
> Move skb freeing from udp recvmsg() path to the cpu
> which allocated/received it, as TCP did in linux-5.17.
> 
> This increases max thoughput by 20% to 30%, depending
> on number of BH producers.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---
>  net/ipv4/udp.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index 7d1444821ee51a19cd5fd0dd5b8d096104c9283c..0c40426628eb2306b609881341a51307c4993871 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -1825,6 +1825,13 @@ void skb_consume_udp(struct sock *sk, struct sk_buff *skb, int len)
>  	if (unlikely(READ_ONCE(udp_sk(sk)->peeking_with_offset)))
>  		sk_peek_offset_bwd(sk, len);
>  
> +	if (!skb_shared(skb)) {
> +		if (unlikely(udp_skb_has_head_state(skb)))
> +			skb_release_head_state(skb);
> +		skb_attempt_defer_free(skb);
> +		return;
> +	}
> +
>  	if (!skb_unref(skb))
>  		return;

What about consolidating the release path with something alternative
like the following, does the skb_unref()/additional smp_rmb() affects
performances badly?

Thanks,

Paolo
---
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index cc3ce0f762ec..ed2e370ad4de 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1836,7 +1836,7 @@ void skb_consume_udp(struct sock *sk, struct
sk_buff *skb, int len)
 	 */
 	if (unlikely(udp_skb_has_head_state(skb)))
 		skb_release_head_state(skb);
-	__consume_stateless_skb(skb);
+	skb_attempt_defer_free(skb);
 }
 EXPORT_IPV6_MOD_GPL(skb_consume_udp);