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

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Message-ID: <aOVs9yvrwkH0dCDJ@boxer>
Date: Tue, 7 Oct 2025 21:41:43 +0200
From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
CC: Eric Dumazet <edumazet@...gle.com>, "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 RFC net-next 1/5] net: add add indirect call wrapper in
 skb_release_head_state()

On Tue, Oct 07, 2025 at 05:26:46PM +0200, Alexander Lobakin wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> Date: Mon,  6 Oct 2025 19:30:59 +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 | 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);
> 
> Not sure, but maybe we could add generic XSk skb destructor here as
> well? Or it's not that important as generic XSk is not the best way to
> use XDP sockets?
> 
> Maciej, what do you think?

I would appreciate it as there has been various attempts to optmize xsk
generic xmit path.

> 
> >  	}
> >  #if IS_ENABLED(CONFIG_NF_CONNTRACK)
> >  	nf_conntrack_put(skb_nfct(skb));
> 
> Thanks,
> Olek