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[TCP]: SACK enhanced FRTO

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Implements the SACK-enhanced FRTO given in RFC4138 using the
variant given in Appendix B.

RFC4138, Appendix B:
  "This means that in order to declare timeout spurious, the TCP
   sender must receive an acknowledgment for non-retransmitted
   segment between SND.UNA and RecoveryPoint in algorithm step 3.
   RecoveryPoint is defined in conservative SACK-recovery
   algorithm [RFC3517]"

The basic version of the FRTO algorithm can still be used also
when SACK is enabled. To enabled SACK-enhanced version, tcp_frto
sysctl is set to 2.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Ilpo Järvinen 2007-02-21 23:16:11 -08:00 committed by David S. Miller
parent 288035f915
commit 4dc2665e36
1 changed files with 65 additions and 11 deletions
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76
net/ipv4/tcp_input.c
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@ -100,6 +100,7 @@ int sysctl_tcp_abc __read_mostly;
#define FLAG_ECE 0x40 /* ECE in this ACK */
#define FLAG_DATA_LOST 0x80 /* SACK detected data lossage. */
#define FLAG_SLOWPATH 0x100 /* Do not skip RFC checks for window update.*/
#define FLAG_ONLY_ORIG_SACKED 0x200 /* SACKs only non-rexmit sent before RTO */
#define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
#define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
@ -110,6 +111,8 @@ int sysctl_tcp_abc __read_mostly;
#define IsFack(tp) ((tp)->rx_opt.sack_ok & 2)
#define IsDSack(tp) ((tp)->rx_opt.sack_ok & 4)
#define IsSackFrto() (sysctl_tcp_frto == 0x2)
#define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
/* Adapt the MSS value used to make delayed ack decision to the
@ -1159,6 +1162,18 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
/* clear lost hint */
tp->retransmit_skb_hint = NULL;
}
/* SACK enhanced F-RTO detection.
* Set flag if and only if non-rexmitted
* segments below frto_highmark are
* SACKed (RFC4138; Appendix B).
* Clearing correct due to in-order walk
*/
if (after(end_seq, tp->frto_highmark)) {
flag &= ~FLAG_ONLY_ORIG_SACKED;
} else {
if (!(sacked & TCPCB_RETRANS))
flag |= FLAG_ONLY_ORIG_SACKED;
}
}
TCP_SKB_CB(skb)->sacked |= TCPCB_SACKED_ACKED;
@ -1240,7 +1255,8 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
/* F-RTO can only be used if these conditions are satisfied:
* - there must be some unsent new data
* - the advertised window should allow sending it
* - TCP has never retransmitted anything other than head
* - TCP has never retransmitted anything other than head (SACK enhanced
* variant from Appendix B of RFC4138 is more robust here)
*/
int tcp_use_frto(struct sock *sk)
{
@ -1252,6 +1268,9 @@ int tcp_use_frto(struct sock *sk)
tp->snd_una + tp->snd_wnd))
return 0;
if (IsSackFrto())
return 1;
/* Avoid expensive walking of rexmit queue if possible */
if (tp->retrans_out > 1)
return 0;
@ -1328,9 +1347,18 @@ void tcp_enter_frto(struct sock *sk)
}
tcp_sync_left_out(tp);
/* Earlier loss recovery underway (see RFC4138; Appendix B).
* The last condition is necessary at least in tp->frto_counter case.
*/
if (IsSackFrto() && (tp->frto_counter ||
((1 << icsk->icsk_ca_state) & (TCPF_CA_Recovery|TCPF_CA_Loss))) &&
after(tp->high_seq, tp->snd_una)) {
tp->frto_highmark = tp->high_seq;
} else {
tp->frto_highmark = tp->snd_nxt;
}
tcp_set_ca_state(sk, TCP_CA_Disorder);
tp->high_seq = tp->snd_nxt;
tp->frto_highmark = tp->snd_nxt;
tp->frto_counter = 1;
}
@ -2566,6 +2594,10 @@ static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
* Rationale: if the RTO was spurious, new ACKs should arrive from the
* original window even after we transmit two new data segments.
*
* SACK version:
* on first step, wait until first cumulative ACK arrives, then move to
* the second step. In second step, the next ACK decides.
*
* F-RTO is implemented (mainly) in four functions:
* - tcp_use_frto() is used to determine if TCP is can use F-RTO
* - tcp_enter_frto() prepares TCP state on RTO if F-RTO is used, it is
@ -2590,16 +2622,38 @@ static int tcp_process_frto(struct sock *sk, u32 prior_snd_una, int flag)
return 1;
}
/* RFC4138 shortcoming in step 2; should also have case c): ACK isn't
* duplicate nor advances window, e.g., opposite dir data, winupdate
*/
if ((tp->snd_una == prior_snd_una) && (flag&FLAG_NOT_DUP) &&
!(flag&FLAG_FORWARD_PROGRESS))
return 1;
if (!IsSackFrto() || IsReno(tp)) {
/* RFC4138 shortcoming in step 2; should also have case c):
* ACK isn't duplicate nor advances window, e.g., opposite dir
* data, winupdate
*/
if ((tp->snd_una == prior_snd_una) && (flag&FLAG_NOT_DUP) &&
!(flag&FLAG_FORWARD_PROGRESS))
return 1;
if (!(flag&FLAG_DATA_ACKED)) {
tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3), flag);
return 1;
if (!(flag&FLAG_DATA_ACKED)) {
tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3),
flag);
return 1;
}
} else {
if (!(flag&FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
/* Prevent sending of new data. */
tp->snd_cwnd = min(tp->snd_cwnd,
tcp_packets_in_flight(tp));
return 1;
}
if ((tp->frto_counter == 2) &&
(!(flag&FLAG_FORWARD_PROGRESS) ||
((flag&FLAG_DATA_SACKED) && !(flag&FLAG_ONLY_ORIG_SACKED)))) {
/* RFC4138 shortcoming (see comment above) */
if (!(flag&FLAG_FORWARD_PROGRESS) && (flag&FLAG_NOT_DUP))
return 1;
tcp_enter_frto_loss(sk, 3, flag);
return 1;
}
}
if (tp->frto_counter == 1) {