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

[Alexander Lobakin <aleksander.lobakin@intel.com>]

From: Jason Xing <kerneljasonxing@gmail.com>
Date: Thu, 23 Oct 2025 16:58:43 +0800

> From: Jason Xing <kernelxing@tencent.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.

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@intel.com>
> Signed-off-by: Jason Xing <kernelxing@tencent.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...

>  
>  /**
>   *  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...

> +
>  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.

Thanks,
Olek