netdev - Re: [PATCH net-next] xsk: add indirect call for xsk_destruct

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Message-ID: <CAL+tcoCjGX8z_UMCy0xidz1kS1EYeH-Q8r_KAo+J0LexwrSnMg@mail.gmail.com>
Date: Thu, 23 Oct 2025 23:02:29 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, 
	pabeni@...hat.com, bjorn@...nel.org, magnus.karlsson@...el.com, 
	maciej.fijalkowski@...el.com, jonathan.lemon@...il.com, sdf@...ichev.me, 
	ast@...nel.org, daniel@...earbox.net, hawk@...nel.org, 
	john.fastabend@...il.com, joe@...a.to, willemdebruijn.kernel@...il.com, 
	bpf@...r.kernel.org, netdev@...r.kernel.org, 
	Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next] xsk: add indirect call for xsk_destruct_skb

On Thu, Oct 23, 2025 at 9:32 PM Alexander Lobakin
<aleksander.lobakin@...el.com> wrote:
>
> From: Jason Xing <kerneljasonxing@...il.com>
> Date: Thu, 23 Oct 2025 16:58:43 +0800
>
> > From: Jason Xing <kernelxing@...cent.com>
> >
> > Since Eric proposed an idea about adding indirect call for UDP and
> > managed to see a huge improvement[1], the same situation can also be
> > applied in xsk scenario.
> >
> > This patch adds an indirect call for xsk and helps current copy mode
> > improve the performance by around 1% stably which was observed with
> > IXGBE at 10Gb/sec loaded. If the throughput grows, the positive effect
> > will be magnified. I applied this patch on top of batch xmit series[2],
> > and was able to see <5% improvement.
>
> Up to 5% is really good.

Yep, but the perf number fluctuates a little bit from our internal
app, not like the first test showing a stable 1% number. so I used '<'
symbol. I think I will add more description around it in the next
respin.

>
> One nit below:
>
> >
> > [1]: https://lore.kernel.org/netdev/20251006193103.2684156-2-edumazet@google.com/
> > [2]: https://lore.kernel.org/all/20251021131209.41491-1-kerneljasonxing@gmail.com/
> >
> > Suggested-by: Alexander Lobakin <aleksander.lobakin@...el.com>
> > Signed-off-by: Jason Xing <kernelxing@...cent.com>
> > ---
> >  include/net/xdp_sock.h | 5 +++++
> >  net/core/skbuff.c      | 8 +++++---
> >  net/xdp/xsk.c          | 2 +-
> >  3 files changed, 11 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
> > index ce587a225661..431de372d0a0 100644
> > --- a/include/net/xdp_sock.h
> > +++ b/include/net/xdp_sock.h
> > @@ -125,6 +125,7 @@ struct xsk_tx_metadata_ops {
> >  int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp);
> >  int __xsk_map_redirect(struct xdp_sock *xs, struct xdp_buff *xdp);
> >  void __xsk_map_flush(struct list_head *flush_list);
> > +void xsk_destruct_skb(struct sk_buff *skb);
>
> I'd suggest wrapping this declaration into INDIRECT_CALLABLE_DELCARE()
> here...

I see. I will add it and verify it tomorrow morning!

>
> >
> >  /**
> >   *  xsk_tx_metadata_to_compl - Save enough relevant metadata information
> > @@ -218,6 +219,10 @@ static inline void __xsk_map_flush(struct list_head *flush_list)
> >  {
> >  }
> >
> > +static inline void xsk_destruct_skb(struct sk_buff *skb)
> > +{
> > +}
>
> ...and guard this stub with CONFIG_MITIGATION_RETPOLINE, then...

At first glance, I'm not sure if it works when CONFIG_INET is
disabled. I will test it and then get back to you here if anything
goes wrong.

>
> > +
> >  static inline void xsk_tx_metadata_to_compl(struct xsk_tx_metadata *meta,
> >                                           struct xsk_tx_metadata_compl *compl)
> >  {
> > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> > index 5b4bc8b1c7d5..00ea38248bd6 100644
> > --- a/net/core/skbuff.c
> > +++ b/net/core/skbuff.c
> > @@ -81,6 +81,7 @@
> >  #include <net/page_pool/helpers.h>
> >  #include <net/psp/types.h>
> >  #include <net/dropreason.h>
> > +#include <net/xdp_sock.h>
> >
> >  #include <linux/uaccess.h>
> >  #include <trace/events/skb.h>
> > @@ -1140,12 +1141,13 @@ void skb_release_head_state(struct sk_buff *skb)
> >       if (skb->destructor) {
> >               DEBUG_NET_WARN_ON_ONCE(in_hardirq());
> >  #ifdef CONFIG_INET
> > -             INDIRECT_CALL_3(skb->destructor,
> > +             INDIRECT_CALL_4(skb->destructor,
> >                               tcp_wfree, __sock_wfree, sock_wfree,
> > +                             xsk_destruct_skb,
> >                               skb);
> >  #else
> > -             INDIRECT_CALL_1(skb->destructor,
> > -                             sock_wfree,
> > +             INDIRECT_CALL_2(skb->destructor,
> > +                             sock_wfree, xsk_destruct_skb,
> >                               skb);
> >
> >  #endif
> > diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> > index 7b0c68a70888..8e6ccb2f79c0 100644
> > --- a/net/xdp/xsk.c
> > +++ b/net/xdp/xsk.c
> > @@ -605,7 +605,7 @@ static u32 xsk_get_num_desc(struct sk_buff *skb)
> >       return XSKCB(skb)->num_descs;
> >  }
> >
> > -static void xsk_destruct_skb(struct sk_buff *skb)
> > +void xsk_destruct_skb(struct sk_buff *skb)
>
> ...replace `static` with INDIRECT_CALLABLE_SCOPE here.
>
> >  {
> >       struct xsk_tx_metadata_compl *compl = &skb_shinfo(skb)->xsk_meta;
>
> The reason is that we want to keep this function static on systems where
> retpoline is not a thing. IOW the same that is done for IP, TCP/UDP, GRO
> etc etc.

I see, thanks for clarifying this.

Thanks,
Jason

>
> Thanks,
> Olek