On Thu, Apr 12, 2012 at 11:05:28AM +0200, Eric Dumazet wrote:
> Most machines dont use UDP encapsulation (L2TP)
>
> Adds a static_key so that udp_queue_rcv_skb() doesnt have to perform a
> test if L2TP never setup the encap_rcv on a socket.
>
> Idea of this patch came after Simon Horman proposal to add a hook on TCP
> as well.
>
> If static_key is not yet enabled, the fast path does a single JMP .
>
> When static_key is enabled, JMP destination is patched to reach the real
> encap_type/encap_rcv logic, possibly adding cache misses.
Thanks Eric,
I have not had a chance to test your code, though it should be easy enough
to do so in the context of Open vSwitch as its CAPWAP implementation makes
use of UDP's encap_rcv (which is how I arrived at adding hook to TCP to
implement STT for Open vSwtich).
I have incorporated your static_key code into a new version of my TCP
encap_rcv patch and that does appear to work. I will post it ASAP.
>
> Signed-off-by: Eric Dumazet <eric.duma...@gmail.com>
> Cc: Simon Horman <ho...@verge.net.au>
> Cc: dev@openvswitch.org
> ---
> include/net/udp.h | 1 +
> net/ipv4/udp.c | 12 +++++++++++-
> net/l2tp/l2tp_core.c | 1 +
> 3 files changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/include/net/udp.h b/include/net/udp.h
> index 5d606d9..9671f5f 100644
> --- a/include/net/udp.h
> +++ b/include/net/udp.h
> @@ -267,4 +267,5 @@ extern void udp_init(void);
> extern int udp4_ufo_send_check(struct sk_buff *skb);
> extern struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
> netdev_features_t features);
> +extern void udp_encap_enable(void);
> #endif /* _UDP_H */
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index fe14105..ad1e0dd 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -107,6 +107,7 @@
> #include <net/checksum.h>
> #include <net/xfrm.h>
> #include <trace/events/udp.h>
> +#include <linux/static_key.h>
> #include "udp_impl.h"
>
> struct udp_table udp_table __read_mostly;
> @@ -1379,6 +1380,14 @@ static int __udp_queue_rcv_skb(struct sock *sk, struct
> sk_buff *skb)
>
> }
>
> +static struct static_key udp_encap_needed __read_mostly;
> +void udp_encap_enable(void)
> +{
> + if (!static_key_enabled(&udp_encap_needed))
> + static_key_slow_inc(&udp_encap_needed);
> +}
> +EXPORT_SYMBOL(udp_encap_enable);
> +
> /* returns:
> * -1: error
> * 0: success
> @@ -1400,7 +1409,7 @@ int udp_queue_rcv_skb(struct sock *sk, struct sk_buff
> *skb)
> goto drop;
> nf_reset(skb);
>
> - if (up->encap_type) {
> + if (static_key_false(&udp_encap_needed) && up->encap_type) {
> int (*encap_rcv)(struct sock *sk, struct sk_buff *skb);
>
> /*
> @@ -1760,6 +1769,7 @@ int udp_lib_setsockopt(struct sock *sk, int level, int
> optname,
> /* FALLTHROUGH */
> case UDP_ENCAP_L2TPINUDP:
> up->encap_type = val;
> + udp_encap_enable();
> break;
> default:
> err = -ENOPROTOOPT;
> diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
> index 89ff8c6..f6732b6 100644
> --- a/net/l2tp/l2tp_core.c
> +++ b/net/l2tp/l2tp_core.c
> @@ -1424,6 +1424,7 @@ int l2tp_tunnel_create(struct net *net, int fd, int
> version, u32 tunnel_id, u32
> /* Mark socket as an encapsulation socket. See net/ipv4/udp.c */
> udp_sk(sk)->encap_type = UDP_ENCAP_L2TPINUDP;
> udp_sk(sk)->encap_rcv = l2tp_udp_encap_recv;
> + udp_encap_enable();
> }
>
> sk->sk_user_data = tunnel;
>
>
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