tcp: record most recent RTT in RACK loss detection

Record the most recent RTT in RACK. It is often identical to the
"ca_rtt_us" values in tcp_clean_rtx_queue. But when the packet has
been retransmitted, RACK choses to believe the ACK is for the
(latest) retransmitted packet if the RTT is over minimum RTT.

This requires passing the arrival time of the most recent ACK to
RACK routines. The timestamp is now recorded in the "ack_time"
in tcp_sacktag_state during the ACK processing.

This patch does not change the RACK algorithm itself. It only adds
the RTT variable to prepare the next main patch.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 3 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 51183bba3835..1439107658c2 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1863,9 +1863,10 @@ extern int sysctl_tcp_recovery;
 /* Use TCP RACK to detect (some) tail and retransmit losses */
 #define TCP_RACK_LOST_RETRANS  0x1
 
-extern void tcp_rack_mark_lost(struct sock *sk);
-extern void tcp_rack_advance(struct tcp_sock *tp,
-                             const struct skb_mstamp *xmit_time, u8 sacked);
+extern void tcp_rack_mark_lost(struct sock *sk, const struct skb_mstamp *now);
+extern void tcp_rack_advance(struct tcp_sock *tp, u8 sacked,
+                             const struct skb_mstamp *xmit_time,
+                             const struct skb_mstamp *ack_time);
 
 /*
  * Save and compile IPv4 options, return a pointer to it