netdev - Re: [PATCH v2 net-next 2/6] net: add add indirect call wrapper in skb_release_head

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Message-ID: <CANn89iLH4VrGyorzPzQU66USsv1UP3XJWQ+MWMTzrceHfUNYVQ@mail.gmail.com>
Date: Wed, 15 Oct 2025 05:46:27 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, 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 v2 net-next 2/6] net: add add indirect call wrapper in skb_release_head_state()

On Wed, Oct 15, 2025 at 5:30 AM Alexander Lobakin
<aleksander.lobakin@...el.com> wrote:
>
> From: Eric Dumazet <edumazet@...gle.com>
> Date: Wed, 15 Oct 2025 05:16:05 -0700
>
> > On Wed, Oct 15, 2025 at 5:02 AM Alexander Lobakin
> > <aleksander.lobakin@...el.com> wrote:
> >>
> >> From: Eric Dumazet <edumazet@...gle.com>
> >> Date: Tue, 14 Oct 2025 17:19:03 +0000
> >>
> >>> 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 | 11 ++++++++++-
> >>>  1 file changed, 10 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> >>> index bc12790017b0..692e3a70e75e 100644
> >>> --- a/net/core/skbuff.c
> >>> +++ b/net/core/skbuff.c
> >>> @@ -1136,7 +1136,16 @@ 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);
> >>> +#ifdef CONFIG_INET
> >>> +             INDIRECT_CALL_3(skb->destructor,
> >>> +                             tcp_wfree, __sock_wfree, sock_wfree,
> >>> +                             skb);
> >>> +#else
> >>> +             INDIRECT_CALL_1(skb->destructor,
> >>> +                             sock_wfree,
> >>> +                             skb);
> >>> +
> >>> +#endif
> >>
> >> Is it just me or seems like you ignored the suggestion/discussion under
> >> v1 of this patch...
> >>
> >
> > I did not. Please send a patch when you can demonstrate the difference.
>
> You "did not", but you didn't reply there, only sent v2 w/o any mention.
>
> >
> > We are not going to add all the possible destructors unless there is evidence.
>
> There are numbers in the original discussion, you'd have noticed if you
> did read.
>
> We only ask to add one more destructor which will help certain
> perf-critical workloads. Add it to the end of the list, so that it won't
> hurt your optimization.
>
> "Send a patch" means you're now changing these lines now and then they
> would be changed once again, why...

I can not test what you propose.

I can drop this patch instead, and keep it in Google kernels, (we had
TCP support for years)

Or... you can send a patch on top of it later.