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Date:	Sat, 22 Sep 2012 15:47:56 -0400 (EDT)
From:	David Miller <>
Subject: Re: [PATCH net-next 3/4] tcp: TCP Fast Open Server - note
 timestamps and retransmits for SYNACK RTT

From: Neal Cardwell <>
Date: Sat, 22 Sep 2012 10:18:56 -0400

> Previously, when using TCP Fast Open a server would return from
> tcp_check_req() before updating snt_synack based on TCP timestamp echo
> replies and whether or not we've retransmitted the SYNACK. The result
> was that (a) for TFO connections using timestamps we used an incorrect
> baseline SYNACK send time (tcp_time_stamp of SYNACK send instead of
> rcv_tsecr), and (b) for TFO connections that do not have TCP
> timestamps but retransmit the SYNACK we took a SYNACK RTT sample when
> we should not take a sample.
> This fix merely moves the snt_synack update logic a bit earlier in the
> function, so that connections using TCP Fast Open will properly do
> these updates when the ACK for the SYNACK arrives.
> Moving this snt_synack update logic means that with TCP_DEFER_ACCEPT
> enabled we do a few instructions of wasted work on each bare ACK, but
> that seems OK.
> Signed-off-by: Neal Cardwell <>

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