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TCP: send full initial window when timestamps are in use

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The fastpath in tcp_output tries to send out
full segments, and avoid sending partial segments by
comparing against the static t_maxseg variable.
That value does not consider tcp options like timestamps,
while the initial window calculation is using
the correct dynamic tcp_maxseg() function.

Due to this interaction, the last, full size segment
is considered too short and not sent out immediately.

Reviewed by:	tuexen
MFC after:	2 weeks
Sponsored by:	NetApp, Inc.
Differential Revision:	https://reviews.freebsd.org/D26478
This commit is contained in:
Richard Scheffenegger 2020-09-25 10:38:19 +00:00
parent 1567c937e2
commit e399566123
3 changed files with 22 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
sys/netinet/tcp.h
View File

@ -80,6 +80,8 @@ struct tcphdr {
u_short th_urp; /* urgent pointer */
};
#define PADTCPOLEN(len) ((((len) / 4) + !!((len) % 4)) * 4)
#define TCPOPT_EOL 0
#define TCPOLEN_EOL 1
#define TCPOPT_PAD 0 /* padding after EOL */

14
sys/netinet/tcp_output.c
View File

@ -590,6 +590,20 @@ tcp_output(struct tcpcb *tp)
if (len) {
if (len >= tp->t_maxseg)
goto send;
/*
* As the TCP header options are now
* considered when setting up the initial
* window, we would not send the last segment
* if we skip considering the option length here.
* Note: this may not work when tcp headers change
* very dynamically in the future.
*/
if ((((tp->t_flags & TF_SIGNATURE) ?
PADTCPOLEN(TCPOLEN_SIGNATURE) : 0) +
((tp->t_flags & TF_RCVD_TSTMP) ?
PADTCPOLEN(TCPOLEN_TIMESTAMP) : 0) +
len) >= tp->t_maxseg)
goto send;
/*
* NOTE! on localhost connections an 'ack' from the remote
* end may occur synchronously with the output and cause

13
sys/netinet/tcp_subr.c
View File

@ -3013,7 +3013,6 @@ tcp_maxseg(const struct tcpcb *tp)
* but this is harmless, since result of tcp_maxseg() is used
* only in cwnd and ssthresh estimations.
*/
#define PAD(len) ((((len) / 4) + !!((len) % 4)) * 4)
if (TCPS_HAVEESTABLISHED(tp->t_state)) {
if (tp->t_flags & TF_RCVD_TSTMP)
optlen = TCPOLEN_TSTAMP_APPA;
@ -3021,26 +3020,26 @@ tcp_maxseg(const struct tcpcb *tp)
optlen = 0;
#if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
if (tp->t_flags & TF_SIGNATURE)
optlen += PAD(TCPOLEN_SIGNATURE);
optlen += PADTCPOLEN(TCPOLEN_SIGNATURE);
#endif
if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks > 0) {
optlen += TCPOLEN_SACKHDR;
optlen += tp->rcv_numsacks * TCPOLEN_SACK;
optlen = PAD(optlen);
optlen = PADTCPOLEN(optlen);
}
} else {
if (tp->t_flags & TF_REQ_TSTMP)
optlen = TCPOLEN_TSTAMP_APPA;
else
optlen = PAD(TCPOLEN_MAXSEG);
optlen = PADTCPOLEN(TCPOLEN_MAXSEG);
if (tp->t_flags & TF_REQ_SCALE)
optlen += PAD(TCPOLEN_WINDOW);
optlen += PADTCPOLEN(TCPOLEN_WINDOW);
#if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
if (tp->t_flags & TF_SIGNATURE)
optlen += PAD(TCPOLEN_SIGNATURE);
optlen += PADTCPOLEN(TCPOLEN_SIGNATURE);
#endif
if (tp->t_flags & TF_SACK_PERMIT)
optlen += PAD(TCPOLEN_SACK_PERMITTED);
optlen += PADTCPOLEN(TCPOLEN_SACK_PERMITTED);
}
#undef PAD
optlen = min(optlen, TCP_MAXOLEN);