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Date: Tue, 19 Jun 2012 19:35:49 -0700
From: Stephen Hemminger <shemminger@...tta.com>
To: David Miller <davem@...emloft.net>
Cc: netdev@...r.kernel.org
Subject: Re: [PATCH v2] ipv4: Early TCP socket demux.
On Tue, 19 Jun 2012 16:39:11 -0700 (PDT)
David Miller <davem@...emloft.net> wrote:
>
> Input packet processing for local sockets involves two major demuxes.
> One for the route and one for the socket.
>
> But we can optimize this down to one demux for certain kinds of local
> sockets.
>
> Currently we only do this for established TCP sockets, but it could
> at least in theory be expanded to other kinds of connections.
>
> If a TCP socket is established then it's identity is fully specified.
>
> This means that whatever input route was used during the three-way
> handshake must work equally well for the rest of the connection since
> the keys will not change.
>
> Once we move to established state, we cache the receive packet's input
> route to use later.
>
> Like the existing cached route in sk->sk_dst_cache used for output
> packets, we have to check for route invalidations using dst->obsolete
> and dst->ops->check().
>
> Early demux occurs outside of a socket locked section, so when a route
> invalidation occurs we defer the fixup of sk->sk_rx_dst until we are
> actually inside of established state packet processing and thus have
> the socket locked.
>
> Signed-off-by: David S. Miller <davem@...emloft.net>
> ---
>
> Changes since v1:
>
> 1) Remove unlikely() from __inet_lookup_skb()
>
> 2) Check for cached route invalidations.
>
> 3) Hook up RX dst when outgoing connection moved to established too,
> previously it was only handling incoming connections.
>
> diff --git a/include/net/inet_hashtables.h b/include/net/inet_hashtables.h
> index 808fc5f..54be028 100644
> --- a/include/net/inet_hashtables.h
> +++ b/include/net/inet_hashtables.h
> @@ -379,10 +379,10 @@ static inline struct sock *__inet_lookup_skb(struct inet_hashinfo *hashinfo,
> const __be16 sport,
> const __be16 dport)
> {
> - struct sock *sk;
> + struct sock *sk = skb_steal_sock(skb);
> const struct iphdr *iph = ip_hdr(skb);
>
> - if (unlikely(sk = skb_steal_sock(skb)))
> + if (sk)
> return sk;
> else
> return __inet_lookup(dev_net(skb_dst(skb)->dev), hashinfo,
> diff --git a/include/net/protocol.h b/include/net/protocol.h
> index 875f489..6c47bf8 100644
> --- a/include/net/protocol.h
> +++ b/include/net/protocol.h
> @@ -34,6 +34,7 @@
>
> /* This is used to register protocols. */
> struct net_protocol {
> + int (*early_demux)(struct sk_buff *skb);
> int (*handler)(struct sk_buff *skb);
> void (*err_handler)(struct sk_buff *skb, u32 info);
> int (*gso_send_check)(struct sk_buff *skb);
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 4a45216..87b424a 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -319,6 +319,7 @@ struct sock {
> unsigned long sk_flags;
> struct dst_entry *sk_dst_cache;
> spinlock_t sk_dst_lock;
> + struct dst_entry *sk_rx_dst;
> atomic_t sk_wmem_alloc;
> atomic_t sk_omem_alloc;
> int sk_sndbuf;
> @@ -1426,6 +1427,7 @@ extern struct sk_buff *sock_rmalloc(struct sock *sk,
> gfp_t priority);
> extern void sock_wfree(struct sk_buff *skb);
> extern void sock_rfree(struct sk_buff *skb);
> +extern void sock_edemux(struct sk_buff *skb);
>
> extern int sock_setsockopt(struct socket *sock, int level,
> int op, char __user *optval,
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 9332f34..6660ffc 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -325,6 +325,7 @@ extern void tcp_v4_err(struct sk_buff *skb, u32);
>
> extern void tcp_shutdown (struct sock *sk, int how);
>
> +extern int tcp_v4_early_demux(struct sk_buff *skb);
> extern int tcp_v4_rcv(struct sk_buff *skb);
>
> extern struct inet_peer *tcp_v4_get_peer(struct sock *sk);
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 9e5b71f..929bdcc 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1465,6 +1465,11 @@ void sock_rfree(struct sk_buff *skb)
> }
> EXPORT_SYMBOL(sock_rfree);
>
> +void sock_edemux(struct sk_buff *skb)
> +{
> + sock_put(skb->sk);
> +}
> +EXPORT_SYMBOL(sock_edemux);
>
> int sock_i_uid(struct sock *sk)
> {
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index e4e8e00..a2bd2d2 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -157,6 +157,7 @@ void inet_sock_destruct(struct sock *sk)
>
> kfree(rcu_dereference_protected(inet->inet_opt, 1));
> dst_release(rcu_dereference_check(sk->sk_dst_cache, 1));
> + dst_release(sk->sk_rx_dst);
> sk_refcnt_debug_dec(sk);
> }
> EXPORT_SYMBOL(inet_sock_destruct);
> @@ -1520,14 +1521,15 @@ static const struct net_protocol igmp_protocol = {
> #endif
>
> static const struct net_protocol tcp_protocol = {
> - .handler = tcp_v4_rcv,
> - .err_handler = tcp_v4_err,
> - .gso_send_check = tcp_v4_gso_send_check,
> - .gso_segment = tcp_tso_segment,
> - .gro_receive = tcp4_gro_receive,
> - .gro_complete = tcp4_gro_complete,
> - .no_policy = 1,
> - .netns_ok = 1,
> + .early_demux = tcp_v4_early_demux,
> + .handler = tcp_v4_rcv,
> + .err_handler = tcp_v4_err,
> + .gso_send_check = tcp_v4_gso_send_check,
> + .gso_segment = tcp_tso_segment,
> + .gro_receive = tcp4_gro_receive,
> + .gro_complete = tcp4_gro_complete,
> + .no_policy = 1,
> + .netns_ok = 1,
> };
>
> static const struct net_protocol udp_protocol = {
> diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
> index 8590144..cb883e1 100644
> --- a/net/ipv4/ip_input.c
> +++ b/net/ipv4/ip_input.c
> @@ -324,19 +324,34 @@ static int ip_rcv_finish(struct sk_buff *skb)
> * how the packet travels inside Linux networking.
> */
> if (skb_dst(skb) == NULL) {
> - int err = ip_route_input_noref(skb, iph->daddr, iph->saddr,
> - iph->tos, skb->dev);
> - if (unlikely(err)) {
> - if (err == -EHOSTUNREACH)
> - IP_INC_STATS_BH(dev_net(skb->dev),
> - IPSTATS_MIB_INADDRERRORS);
> - else if (err == -ENETUNREACH)
> - IP_INC_STATS_BH(dev_net(skb->dev),
> - IPSTATS_MIB_INNOROUTES);
> - else if (err == -EXDEV)
> - NET_INC_STATS_BH(dev_net(skb->dev),
> - LINUX_MIB_IPRPFILTER);
> - goto drop;
> + const struct net_protocol *ipprot;
> + int protocol = iph->protocol;
> + int hash, err;
> +
> + hash = protocol & (MAX_INET_PROTOS - 1);
> +
> + rcu_read_lock();
> + ipprot = rcu_dereference(inet_protos[hash]);
> + err = -ENOENT;
> + if (ipprot && ipprot->early_demux)
> + err = ipprot->early_demux(skb);
> + rcu_read_unlock();
> +
> + if (err) {
> + err = ip_route_input_noref(skb, iph->daddr, iph->saddr,
> + iph->tos, skb->dev);
> + if (unlikely(err)) {
> + if (err == -EHOSTUNREACH)
> + IP_INC_STATS_BH(dev_net(skb->dev),
> + IPSTATS_MIB_INADDRERRORS);
> + else if (err == -ENETUNREACH)
> + IP_INC_STATS_BH(dev_net(skb->dev),
> + IPSTATS_MIB_INNOROUTES);
> + else if (err == -EXDEV)
> + NET_INC_STATS_BH(dev_net(skb->dev),
> + LINUX_MIB_IPRPFILTER);
> + goto drop;
> + }
> }
> }
>
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index b224eb8..8416f8a 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -5518,6 +5518,18 @@ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
> struct tcp_sock *tp = tcp_sk(sk);
> int res;
>
> + if (sk->sk_rx_dst) {
> + struct dst_entry *dst = sk->sk_rx_dst;
> + if (unlikely(dst->obsolete)) {
> + if (dst->ops->check(dst, 0) == NULL) {
> + dst_release(dst);
> + sk->sk_rx_dst = NULL;
> + }
> + }
> + }
> + if (unlikely(sk->sk_rx_dst == NULL))
> + sk->sk_rx_dst = dst_clone(skb_dst(skb));
> +
> /*
> * Header prediction.
> * The code loosely follows the one in the famous
> @@ -5729,8 +5741,10 @@ void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
>
> tcp_set_state(sk, TCP_ESTABLISHED);
>
> - if (skb != NULL)
> + if (skb != NULL) {
> + sk->sk_rx_dst = dst_clone(skb_dst(skb));
> security_inet_conn_established(sk, skb);
> + }
>
> /* Make sure socket is routed, for correct metrics. */
> icsk->icsk_af_ops->rebuild_header(sk);
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index fda2ca1..13857df 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -1671,6 +1671,52 @@ csum_err:
> }
> EXPORT_SYMBOL(tcp_v4_do_rcv);
>
> +int tcp_v4_early_demux(struct sk_buff *skb)
> +{
> + struct net *net = dev_net(skb->dev);
> + const struct iphdr *iph;
> + const struct tcphdr *th;
> + struct sock *sk;
> + int err;
> +
> + err = -ENOENT;
> + if (skb->pkt_type != PACKET_HOST)
> + goto out_err;
> +
> + if (!pskb_may_pull(skb, ip_hdrlen(skb) + sizeof(struct tcphdr)))
> + goto out_err;
> +
> + iph = ip_hdr(skb);
> + th = (struct tcphdr *) ((char *)iph + ip_hdrlen(skb));
> +
> + if (th->doff < sizeof(struct tcphdr) / 4)
> + goto out_err;
> +
> + if (!pskb_may_pull(skb, ip_hdrlen(skb) + th->doff * 4))
> + goto out_err;
> +
> + sk = __inet_lookup_established(net, &tcp_hashinfo,
> + iph->saddr, th->source,
> + iph->daddr, th->dest,
> + skb->dev->ifindex);
> + if (sk) {
> + skb->sk = sk;
> + skb->destructor = sock_edemux;
> + if (sk->sk_state != TCP_TIME_WAIT) {
> + struct dst_entry *dst = sk->sk_rx_dst;
> + if (dst)
> + dst = dst_check(dst, 0);
> + if (dst) {
> + skb_dst_set_noref(skb, dst);
> + err = 0;
> + }
> + }
> + }
> +
> +out_err:
> + return err;
> +}
> +
> /*
> * From tcp_input.c
> */
> diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
> index cb01531..72b7c63 100644
> --- a/net/ipv4/tcp_minisocks.c
> +++ b/net/ipv4/tcp_minisocks.c
> @@ -445,6 +445,8 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
> struct tcp_sock *oldtp = tcp_sk(sk);
> struct tcp_cookie_values *oldcvp = oldtp->cookie_values;
>
> + newsk->sk_rx_dst = dst_clone(skb_dst(skb));
> +
> /* TCP Cookie Transactions require space for the cookie pair,
> * as it differs for each connection. There is no need to
> * copy any s_data_payload stored at the original socket.
> --
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Any benchmark numbers?
I think the number of ref count operations per packet is going to be
the next line in the sand.
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