netdev - Re: [PATCH RFC net-next 1/5] net: add add indirect call wrapper in skb_release_head

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Message-ID: <CANn89i+J4aHWWsOVBhUVz6qqX8_O7zzjZOvDKCfD7NAiBrQpVg@mail.gmail.com>
Date: Mon, 6 Oct 2025 12:38:54 -0700
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>, Jamal Hadi Salim <jhs@...atatu.com>, 
	Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>, 
	Kuniyuki Iwashima <kuniyu@...gle.com>, Willem de Bruijn <willemb@...gle.com>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com
Subject: Re: [PATCH RFC net-next 1/5] net: add add indirect call wrapper in skb_release_head_state()

On Mon, Oct 6, 2025 at 12:31 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> While stress testing UDP senders on a host with expensive indirect
> calls, I found cpus processing TX completions where showing
> a very high cost (20%) in sock_wfree() due to
> CONFIG_MITIGATION_RETPOLINE=y.
>
> Take care of TCP and UDP TX destructors and use INDIRECT_CALL_3() macro.
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---
>  net/core/skbuff.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index bc12790017b0b5c0be99f8fb9d362b3730fa4eb0..c9c06f9a8d6085f8d0907b412e050a60c835a6e8 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -1136,7 +1136,9 @@ void skb_release_head_state(struct sk_buff *skb)
>         skb_dst_drop(skb);
>         if (skb->destructor) {
>                 DEBUG_NET_WARN_ON_ONCE(in_hardirq());
> -               skb->destructor(skb);
> +               INDIRECT_CALL_3(skb->destructor,
> +                               tcp_wfree, __sock_wfree, sock_wfree,
> +                               skb);

This will probably not compile well with  "# CONFIG_INET is not set".

I will fix this when submitting the non RFC verson.