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Commit 375fe02c authored by Yuchung Cheng's avatar Yuchung Cheng Committed by David S. Miller
Browse files

tcp: consolidate SYNACK RTT sampling 



The first patch consolidates SYNACK and other RTT measurement to use a
central function tcp_ack_update_rtt(). A (small) bonus is now SYNACK
RTT measurement happens after PAWS check, potentially reducing the
impact of RTO seeding on bad TCP timestamps values.

Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent c3f51d5f

include/net/tcp.h

+0 −9
Original line number Diff line number Diff line
@@ -1094,15 +1094,6 @@ static inline void tcp_openreq_init(struct request_sock *req, 
	ireq->loc_port = tcp_hdr(skb)->dest;

}



/* Compute time elapsed between SYNACK and the ACK completing 3WHS */

static inline void tcp_synack_rtt_meas(struct sock *sk,

				       struct request_sock *req)

{

	if (tcp_rsk(req)->snt_synack)

		tcp_valid_rtt_meas(sk,

		    tcp_time_stamp - tcp_rsk(req)->snt_synack);

}



extern void tcp_enter_memory_pressure(struct sock *sk);



static inline int keepalive_intvl_when(const struct tcp_sock *tp)

net/ipv4/tcp_input.c

+12 −2
Original line number Diff line number Diff line
@@ -2853,6 +2853,17 @@ static inline void tcp_ack_update_rtt(struct sock *sk, const int flag, 
		tcp_ack_no_tstamp(sk, seq_rtt, flag);

}



/* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */

static void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req)

{

	struct tcp_sock *tp = tcp_sk(sk);

	s32 seq_rtt = -1;



	if (tp->lsndtime && !tp->total_retrans)

		seq_rtt = tcp_time_stamp - tp->lsndtime;

	tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, seq_rtt);

}



static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)

{

	const struct inet_connection_sock *icsk = inet_csk(sk);
@@ -5624,9 +5635,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb, 
		 * so release it.

		 */

		if (req) {

			tcp_synack_rtt_meas(sk, req);

			tp->total_retrans = req->num_retrans;



			reqsk_fastopen_remove(sk, req, false);

		} else {

			/* Make sure socket is routed, for correct metrics. */
@@ -5651,6 +5660,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb, 
		tp->snd_una = TCP_SKB_CB(skb)->ack_seq;

		tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;

		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);

		tcp_synack_rtt_meas(sk, req);



		if (tp->rx_opt.tstamp_ok)

			tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;

net/ipv4/tcp_ipv4.c

+0 −2
Original line number Diff line number Diff line
@@ -1671,8 +1671,6 @@ struct sock *tcp_v4_syn_recv_sock(struct sock *sk, struct sk_buff *skb, 
		newtp->advmss = tcp_sk(sk)->rx_opt.user_mss;



	tcp_initialize_rcv_mss(newsk);

	tcp_synack_rtt_meas(newsk, req);

	newtp->total_retrans = req->num_retrans;



#ifdef CONFIG_TCP_MD5SIG

	/* Copy over the MD5 key from the original socket */

net/ipv4/tcp_minisocks.c

+2 −6
Original line number Diff line number Diff line
@@ -411,6 +411,8 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req, 
		newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;

		tcp_enable_early_retrans(newtp);

		newtp->tlp_high_seq = 0;

		newtp->lsndtime = treq->snt_synack;

		newtp->total_retrans = req->num_retrans;



		/* So many TCP implementations out there (incorrectly) count the

		 * initial SYN frame in their delayed-ACK and congestion control
@@ -666,12 +668,6 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, 
	if (!(flg & TCP_FLAG_ACK))

		return NULL;



	/* Got ACK for our SYNACK, so update baseline for SYNACK RTT sample. */

	if (tmp_opt.saw_tstamp && tmp_opt.rcv_tsecr)

		tcp_rsk(req)->snt_synack = tmp_opt.rcv_tsecr;

	else if (req->num_retrans) /* don't take RTT sample if retrans && ~TS */

		tcp_rsk(req)->snt_synack = 0;



	/* For Fast Open no more processing is needed (sk is the

	 * child socket).

	 */

net/ipv6/tcp_ipv6.c

+0 −2
Original line number Diff line number Diff line
@@ -1237,8 +1237,6 @@ static struct sock * tcp_v6_syn_recv_sock(struct sock *sk, struct sk_buff *skb, 
		newtp->advmss = tcp_sk(sk)->rx_opt.user_mss;



	tcp_initialize_rcv_mss(newsk);

	tcp_synack_rtt_meas(newsk, req);

	newtp->total_retrans = req->num_retrans;



	newinet->inet_daddr = newinet->inet_saddr = LOOPBACK4_IPV6;

	newinet->inet_rcv_saddr = LOOPBACK4_IPV6;