netdev - Re: [PATCH net-next] tcp: switch snt_synack back to measuring transmit time of first SYNACK

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Message-Id: <20140707.192652.2078847253054450980.davem@davemloft.net>
Date:	Mon, 07 Jul 2014 19:26:52 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	ncardwell@...gle.com
Cc:	netdev@...r.kernel.org, ycheng@...gle.com,
	octavian.purdila@...el.com, hkchu@...gle.com
Subject: Re: [PATCH net-next] tcp: switch snt_synack back to measuring
 transmit time of first SYNACK

From: Neal Cardwell <ncardwell@...gle.com>
Date: Mon, 30 Jun 2014 15:09:49 -0400

> Always store in snt_synack the time at which the server received the
> first client SYN and attempted to send the first SYNACK.
> 
> Recent commit aa27fc501 ("tcp: tcp_v[46]_conn_request: fix snt_synack
> initialization") resolved an inconsistency between IPv4 and IPv6 in
> the initialization of snt_synack. This commit brings back the idea
> from 843f4a55e (tcp: use tcp_v4_send_synack on first SYN-ACK), which
> was going for the original behavior of snt_synack from the commit
> where it was added in 9ad7c049f0f79 ("tcp: RFC2988bis + taking RTT
> sample from 3WHS for the passive open side") in v3.1.
> 
> In addition to being simpler (and probably a tiny bit faster),
> unconditionally storing the time of the first SYNACK attempt has been
> useful because it allows calculating a performance metric quantifying
> how long it took to establish a passive TCP connection.
> 
> Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>

Applied, thanks.
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