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

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Message-ID: <CAE1zotL1kwk3NfzEAYaM5fdOJihOfn04MQz4qGaVs3LybbVtvg@mail.gmail.com>
Date:	Tue, 1 Jul 2014 11:33:10 +0300
From:	Octavian Purdila <octavian.purdila@...el.com>
To:	Neal Cardwell <ncardwell@...gle.com>
Cc:	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Yuchung Cheng <ycheng@...gle.com>, Jerry Chu <hkchu@...gle.com>
Subject: Re: [PATCH net-next] tcp: switch snt_synack back to measuring
 transmit time of first SYNACK

On Mon, Jun 30, 2014 at 10:09 PM, Neal Cardwell <ncardwell@...gle.com> wrote:
> 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.
>

Acked-by: Octavian Purdila <octavian.purdila@...el.com>
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