Merge branch 'tcp-synflood-perf'

Eric Dumazet says:

====================
tcp: final work on SYNFLOOD behavior

In the first patch, I remove the costly association of SYNACK+COOKIES
to a listener. I believe other parts of the stack should be ready.

The second patch removes a useless write into listener socket
in tcp_rcv_state_process(), incurring false sharing in
tcp_conn_request()

Performance under SYNFLOOD goes from 3.2 Mpps to 6 Mpps.

Test was using a single TCP listener, on a host with 8 RX queues
on the NIC, and 24 cores (48 ht)
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/tcp.h

@@ -452,10 +452,15 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
 int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb);
 int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len);
 int tcp_connect(struct sock *sk);
+enum tcp_synack_type {
+	TCP_SYNACK_NORMAL,
+	TCP_SYNACK_FASTOPEN,
+	TCP_SYNACK_COOKIE,
+};
 struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
 				struct request_sock *req,
 				struct tcp_fastopen_cookie *foc,
-				bool attach_req);
+				enum tcp_synack_type synack_type);
 int tcp_disconnect(struct sock *sk, int flags);
 
 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb);
@@ -1728,7 +1733,7 @@ struct tcp_request_sock_ops {
 	int (*send_synack)(const struct sock *sk, struct dst_entry *dst,
 			   struct flowi *fl, struct request_sock *req,
 			   struct tcp_fastopen_cookie *foc,
-			   bool attach_req);
+			   enum tcp_synack_type synack_type);
 };
 
 #ifdef CONFIG_SYN_COOKIES

net/ipv4/tcp_input.c

@@ -5796,8 +5796,6 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 	int queued = 0;
 	bool acceptable;
 
-	tp->rx_opt.saw_tstamp = 0;
-
 	switch (sk->sk_state) {
 	case TCP_CLOSE:
 		goto discard;
@@ -5838,6 +5836,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 		goto discard;
 
 	case TCP_SYN_SENT:
+		tp->rx_opt.saw_tstamp = 0;
 		queued = tcp_rcv_synsent_state_process(sk, skb, th);
 		if (queued >= 0)
 			return queued;
@@ -5849,6 +5848,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 		return 0;
 	}
 
+	tp->rx_opt.saw_tstamp = 0;
 	req = tp->fastopen_rsk;
 	if (req) {
 		WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
@@ -6327,7 +6327,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 	}
 	if (fastopen_sk) {
 		af_ops->send_synack(fastopen_sk, dst, &fl, req,
-				    &foc, false);
+				    &foc, TCP_SYNACK_FASTOPEN);
 		/* Add the child socket directly into the accept queue */
 		inet_csk_reqsk_queue_add(sk, req, fastopen_sk);
 		sk->sk_data_ready(sk);
@@ -6337,8 +6337,9 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 		tcp_rsk(req)->tfo_listener = false;
 		if (!want_cookie)
 			inet_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
-		af_ops->send_synack(sk, dst, &fl, req,
-				    &foc, !want_cookie);
+		af_ops->send_synack(sk, dst, &fl, req, &foc,
+				    !want_cookie ? TCP_SYNACK_NORMAL :
+						   TCP_SYNACK_COOKIE);
 		if (want_cookie) {
 			reqsk_free(req);
 			return 0;

net/ipv4/tcp_ipv4.c

@@ -830,7 +830,7 @@ static int tcp_v4_send_synack(const struct sock *sk, struct dst_entry *dst,
 			      struct flowi *fl,
 			      struct request_sock *req,
 			      struct tcp_fastopen_cookie *foc,
-				  bool attach_req)
+			      enum tcp_synack_type synack_type)
 {
 	const struct inet_request_sock *ireq = inet_rsk(req);
 	struct flowi4 fl4;
@@ -841,7 +841,7 @@ static int tcp_v4_send_synack(const struct sock *sk, struct dst_entry *dst,
 	if (!dst && (dst = inet_csk_route_req(sk, &fl4, req)) == NULL)
 		return -1;
 
-	skb = tcp_make_synack(sk, dst, req, foc, attach_req);
+	skb = tcp_make_synack(sk, dst, req, foc, synack_type);
 
 	if (skb) {
 		__tcp_v4_send_check(skb, ireq->ir_loc_addr, ireq->ir_rmt_addr);

net/ipv4/tcp_output.c

@@ -2944,7 +2944,7 @@ int tcp_send_synack(struct sock *sk)
 struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
 				struct request_sock *req,
 				struct tcp_fastopen_cookie *foc,
-				bool attach_req)
+				enum tcp_synack_type synack_type)
 {
 	struct inet_request_sock *ireq = inet_rsk(req);
 	const struct tcp_sock *tp = tcp_sk(sk);
@@ -2964,14 +2964,22 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
 	/* Reserve space for headers. */
 	skb_reserve(skb, MAX_TCP_HEADER);
 
-	if (attach_req) {
+	switch (synack_type) {
+	case TCP_SYNACK_NORMAL:
 		skb_set_owner_w(skb, req_to_sk(req));
-	} else {
+		break;
+	case TCP_SYNACK_COOKIE:
+		/* Under synflood, we do not attach skb to a socket,
+		 * to avoid false sharing.
+		 */
+		break;
+	case TCP_SYNACK_FASTOPEN:
 		/* sk is a const pointer, because we want to express multiple
 		 * cpu might call us concurrently.
 		 * sk->sk_wmem_alloc in an atomic, we can promote to rw.
 		 */
 		skb_set_owner_w(skb, (struct sock *)sk);
+		break;
 	}
 	skb_dst_set(skb, dst);
 
@@ -3516,7 +3524,7 @@ int tcp_rtx_synack(const struct sock *sk, struct request_sock *req)
 	int res;
 
 	tcp_rsk(req)->txhash = net_tx_rndhash();
-	res = af_ops->send_synack(sk, NULL, &fl, req, NULL, true);
+	res = af_ops->send_synack(sk, NULL, &fl, req, NULL, TCP_SYNACK_NORMAL);
 	if (!res) {
 		TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);

net/ipv6/tcp_ipv6.c

@@ -439,7 +439,7 @@ static int tcp_v6_send_synack(const struct sock *sk, struct dst_entry *dst,
 			      struct flowi *fl,
 			      struct request_sock *req,
 			      struct tcp_fastopen_cookie *foc,
-			      bool attach_req)
+			      enum tcp_synack_type synack_type)
 {
 	struct inet_request_sock *ireq = inet_rsk(req);
 	struct ipv6_pinfo *np = inet6_sk(sk);
@@ -452,7 +452,7 @@ static int tcp_v6_send_synack(const struct sock *sk, struct dst_entry *dst,
 					       IPPROTO_TCP)) == NULL)
 		goto done;
 
-	skb = tcp_make_synack(sk, dst, req, foc, attach_req);
+	skb = tcp_make_synack(sk, dst, req, foc, synack_type);
 
 	if (skb) {
 		__tcp_v6_send_check(skb, &ireq->ir_v6_loc_addr,