netdev - RE: [PATCH net-next] udp: introduce and use indirect call wrapper for data ready()

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Date: Mon, 17 Jul 2023 09:44:33 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Paolo Abeni <pabeni@...hat.com>, 
 netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 David Ahern <dsahern@...nel.org>
Subject: RE: [PATCH net-next] udp: introduce and use indirect call wrapper for
 data ready()

Paolo Abeni wrote:
> In most cases UDP sockets use the default data ready callback.
> This patch Introduces and uses a specific indirect call wrapper for
> such callback to avoid an indirect call in fastpath.
> 
> The above gives small but measurable performance gain under UDP flood.

Interesting. I recently wrote a patch to add indirect call wrappers
around getfrag (ip_generic_getfrag), expecting that to improve  UDP
senders. Since it's an indirect call on each send call. Not sent,
because I did not see measurable gains, at least with a udp_rr bench.

> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> ---
> Note that this helper could be used for TCP, too. I did not send such
> patch right away because in my tests the perf delta there is below the
> noise level even in RR scenarios and the patch would be a little more
> invasive - there are more sk_data_ready() invocation places.
> ---
>  include/net/sock.h | 4 ++++
>  net/ipv4/udp.c     | 2 +-
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 2eb916d1ff64..1b26dbecdcca 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -2947,6 +2947,10 @@ static inline bool sk_dev_equal_l3scope(struct sock *sk, int dif)
>  }
>  
>  void sock_def_readable(struct sock *sk);
> +static inline void sk_data_ready(struct sock *sk)
> +{
> +	INDIRECT_CALL_1(sk->sk_data_ready, sock_def_readable, sk);
> +}
>

Why introduce a static inline in the header for this?

To reuse it in other protocols later?

>  int sock_bindtoindex(struct sock *sk, int ifindex, bool lock_sk);
>  void sock_set_timestamp(struct sock *sk, int optname, bool valbool);
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index 42a96b3547c9..5aec1854b711 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -1553,7 +1553,7 @@ int __udp_enqueue_schedule_skb(struct sock *sk, struct sk_buff *skb)
>  	spin_unlock(&list->lock);
>  
>  	if (!sock_flag(sk, SOCK_DEAD))
> -		sk->sk_data_ready(sk);
> +		sk_data_ready(sk);
>  
>  	busylock_release(busy);
>  	return 0;
> -- 
> 2.41.0
>