Re: [PATCH][v4] tcp: fix ICMP-RTO war

From: "Ilpo Järvinen" <redacted>
Date: Tue, 16 Feb 2010 14:45:25 +0200 (EET)

On Wed, 10 Feb 2010, Damian Lukowski wrote:

quoted

@@ -5783,12 +5783,10 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
 
 				/* tcp_ack considers this ACK as duplicate
 				 * and does not calculate rtt.
-				 * Fix it at least with timestamps.
+				 * Force it here.
 				 */
-				if (tp->rx_opt.saw_tstamp &&
-				    tp->rx_opt.rcv_tsecr && !tp->srtt)
-					tcp_ack_saw_tstamp(sk, 0);
-
+				tcp_ack_update_rtt(sk, 0, 0);
+

...Here a zero seq_rtt is given to RTT estimator (it will be effective 
only in the case w/o timestamps, TS case recalculates it from the stored 
timestamps). Maybe we could use some field (timestamp related one comes to 
my mind) in request sock to get a real RTT estimate for non-timestamp case 
too. ...It seems possible to me, though tricky because the request_sock is 
no longer that easily available here so some parameter passing would be 
needed.

Agreed.

But even more simply I think we should make even the current
tcp_ack_update_rtt() call here conditional on at least
tp->srtt being zero.

Damian do you at least agree with that?