From: David Miller <davem@davemloft.net>
To: ncardwell@google.com
Cc: avagin@openvz.org, netdev@vger.kernel.org, criu@openvz.org,
linux-kernel@vger.kernel.org, kuznet@ms2.inr.ac.ru,
jmorris@namei.org, yoshfuji@linux-ipv6.org, kaber@trash.net,
edumazet@google.com, ycheng@google.com, xemul@parallels.com,
davej@redhat.com, mtk.manpages@gmail.com
Subject: Re: [PATCH net-next] tcp: add ability to set a timestamp offset
Date: Tue, 22 Jan 2013 16:24:10 -0500 (EST) [thread overview]
Message-ID: <20130122.162410.201366520574331812.davem@davemloft.net> (raw)
In-Reply-To: <CADVnQynxigC7wSW6D1WQNZwxoBd7fpySa8eGN0W4wrh7WtHV4Q@mail.gmail.com>
From: Neal Cardwell <ncardwell@google.com>
Date: Tue, 22 Jan 2013 16:18:04 -0500
> On Tue, Jan 22, 2013 at 3:52 PM, Andrey Vagin <avagin@openvz.org> wrote:
>> If a TCP socket will get live-migrated from one box to another the
>> timestamps (which are typically ON) will get screwed up -- the new
>> kernel will generate TS values that has nothing to do with what they
>> were on dump. The solution is to yet again fix the kernel and put a
>> "timestamp offset" on a socket.
>
> One serious issue with this patch is that outgoing timestamp values
> will no longer correspond to tcp_time_stamp, so echoed timestamp
> values will also no longer have a meaningful relationship to
> tcp_time_stamp. That violates assumptions made in several places in
> the code, which assumes that we can compare echoed timestamp values to
> tcp_time_stamp; for example, there are several places where we do
> things like subtracting:
> tcp_time_stamp - tp->rx_opt.rcv_tsecr
> to find the estimated RTT for a segment.
Right, this change seems pretty bogus as-is.
next prev parent reply other threads:[~2013-01-22 21:24 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-22 20:52 [PATCH net-next] tcp: add ability to set a timestamp offset Andrey Vagin
2013-01-22 21:16 ` Rick Jones
2013-01-22 21:18 ` Neal Cardwell
2013-01-22 21:24 ` David Miller [this message]
-- strict thread matches above, loose matches on Subject: below --
2013-02-11 15:50 Andrey Vagin
2013-02-13 18:22 ` David Miller
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