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Commit 86c6a2c7 authored by Neal Cardwell's avatar Neal Cardwell Committed by David S. Miller
Browse files

tcp: switch snt_synack back to measuring transmit time of first SYNACK 



Always store in snt_synack the time at which the server received the
first client SYN and attempted to send the first SYNACK.

Recent commit aa27fc50 ("tcp: tcp_v[46]_conn_request: fix snt_synack
initialization") resolved an inconsistency between IPv4 and IPv6 in
the initialization of snt_synack. This commit brings back the idea
from 843f4a55 (tcp: use tcp_v4_send_synack on first SYN-ACK), which
was going for the original behavior of snt_synack from the commit
where it was added in 9ad7c049 ("tcp: RFC2988bis + taking RTT
sample from 3WHS for the passive open side") in v3.1.

In addition to being simpler (and probably a tiny bit faster),
unconditionally storing the time of the first SYNACK attempt has been
useful because it allows calculating a performance metric quantifying
how long it took to establish a passive TCP connection.

Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
Cc: Octavian Purdila <octavian.purdila@intel.com>
Cc: Jerry Chu <hkchu@google.com>
Acked-by: default avatarOctavian Purdila <octavian.purdila@intel.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 0b88e704

include/net/tcp.h

+1 −1
Original line number Original line Diff line number Diff line
@@ -1093,7 +1093,7 @@ static inline void tcp_openreq_init(struct request_sock *req, 
	req->cookie_ts = 0;

	req->cookie_ts = 0;

	tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;

	tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;

	tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;

	tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;

	tcp_rsk(req)->snt_synack = 0;

	tcp_rsk(req)->snt_synack = tcp_time_stamp;

	req->mss = rx_opt->mss_clamp;

	req->mss = rx_opt->mss_clamp;

	req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;

	req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;

	ireq->tstamp_ok = rx_opt->tstamp_ok;

	ireq->tstamp_ok = rx_opt->tstamp_ok;

net/ipv4/tcp_ipv4.c

+0 −2
Original line number Original line Diff line number Diff line
@@ -838,8 +838,6 @@ static int tcp_v4_send_synack(struct sock *sk, struct dst_entry *dst, 
					    ireq->ir_rmt_addr,

					    ireq->ir_rmt_addr,

					    ireq->opt);

					    ireq->opt);

		err = net_xmit_eval(err);

		err = net_xmit_eval(err);

		if (!tcp_rsk(req)->snt_synack && !err)

			tcp_rsk(req)->snt_synack = tcp_time_stamp;

	}

	}





	return err;

	return err;

net/ipv6/tcp_ipv6.c

+0 −2
Original line number Original line Diff line number Diff line
@@ -498,8 +498,6 @@ static int tcp_v6_send_synack(struct sock *sk, struct dst_entry *dst, 
		skb_set_queue_mapping(skb, queue_mapping);

		skb_set_queue_mapping(skb, queue_mapping);

		err = ip6_xmit(sk, skb, fl6, np->opt, np->tclass);

		err = ip6_xmit(sk, skb, fl6, np->opt, np->tclass);

		err = net_xmit_eval(err);

		err = net_xmit_eval(err);

		if (!tcp_rsk(req)->snt_synack && !err)

			tcp_rsk(req)->snt_synack = tcp_time_stamp;

	}

	}





done:

done: