From: SeongJae Park <sj38.park@gmail.com>
To: Neal Cardwell <ncardwell@google.com>
Cc: SeongJae Park <sj38.park@gmail.com>,
Eric Dumazet <eric.dumazet@gmail.com>,
sjpark@amazon.com, Eric Dumazet <edumazet@google.com>,
David Miller <davem@davemloft.net>,
shuah@kernel.org, Netdev <netdev@vger.kernel.org>,
linux-kselftest@vger.kernel.org,
LKML <linux-kernel@vger.kernel.org>,
aams@amazon.com, SeongJae Park <sjpark@amazon.de>,
Yuchung Cheng <ycheng@google.com>
Subject: Re: Re: Re: [PATCH 2/3] tcp: Reduce SYN resend delay if a suspicous ACK is received
Date: Sat, 1 Feb 2020 07:08:43 +0100 [thread overview]
Message-ID: <20200201060843.21626-1-sj38.park@gmail.com> (raw)
In-Reply-To: <CADVnQy=oFmmG-Z9QMafWLcALOBgohADgwScn2r+7CGFNAw5jvw@mail.gmail.com> (raw)
On Fri, 31 Jan 2020 22:55:34 -0500 Neal Cardwell <ncardwell@google.com> wrote:
> On Fri, Jan 31, 2020 at 5:18 PM SeongJae Park <sj38.park@gmail.com> wrote:
> >
> > On Fri, 31 Jan 2020 17:11:35 -0500 Neal Cardwell <ncardwell@google.com> wrote:
> >
> > > On Fri, Jan 31, 2020 at 1:12 PM Eric Dumazet <eric.dumazet@gmail.com> wrote:
> > > >
> > > >
> > > >
> > > > On 1/31/20 7:10 AM, Neal Cardwell wrote:
> > > > > On Fri, Jan 31, 2020 at 7:25 AM <sjpark@amazon.com> wrote:
> > > > >>
> > > > >> From: SeongJae Park <sjpark@amazon.de>
> > > > >>
> > > > >> When closing a connection, the two acks that required to change closing
> > > > >> socket's status to FIN_WAIT_2 and then TIME_WAIT could be processed in
> > > > >> reverse order. This is possible in RSS disabled environments such as a
> > > > >> connection inside a host.
> > [...]
> > >
> > > I looked into fixing this, but my quick reading of the Linux
> > > tcp_rcv_state_process() code is that it should behave correctly and
> > > that a connection in FIN_WAIT_1 that receives a FIN/ACK should move to
> > > TIME_WAIT.
> > >
> > > SeongJae, do you happen to have a tcpdump trace of the problematic
> > > sequence where the "process A" ends up in FIN_WAIT_2 when it should be
> > > in TIME_WAIT?
> >
> > Hi Neal,
> >
> >
> > Yes, I have. You can get it from the previous discussion for this patchset
> > (https://lore.kernel.org/bpf/20200129171403.3926-1-sjpark@amazon.com/). As it
> > also has a reproducer program and how I got the tcpdump trace, I believe you
> > could get your own trace, too. If you have any question or need help, feel
> > free to let me know. :)
>
> Great. Thank you for the pointer.
>
> I had one quick question: in the message:
> https://lore.kernel.org/bpf/20200129171403.3926-1-sjpark@amazon.com/
> ... it showed a trace with the client sending a RST/ACK, but this
> email thread shows a FIN/ACK. I am curious about the motivation for
> the difference?
RST/ACK is traced if LINGER socket option is applied in the reproduce program,
and FIN/ACK is traced if it is not applied. LINGER applied version shows the
spikes more frequently, but the main problem logic has no difference. I
confirmed this by testing both of the two versions.
In the previous discussion, I showed the LINGER applied trace. However, as
many other documents are using FIN/ACK, I changed the trace to FIN/ACK version
in this patchset for better understanding. I will comment that it doesn't
matter whether it is FIN/ACK or RST/ACK in the next spin.
Thanks,
SeongJae Park
>
> Anyway, thanks for the report, and thanks to Eric for further clarifying!
>
> neal
>
next prev parent reply other threads:[~2020-02-01 6:09 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-31 12:24 [PATCH 0/3] Fix reconnection latency caused by FIN/ACK handling race sjpark
2020-01-31 12:24 ` [PATCH 1/3] net/ipv4/inet_timewait_sock: Fix inconsistent comments sjpark
2020-01-31 14:54 ` Eric Dumazet
2020-01-31 15:09 ` sjpark
2020-01-31 12:24 ` [PATCH 2/3] tcp: Reduce SYN resend delay if a suspicous ACK is received sjpark
2020-01-31 15:01 ` Eric Dumazet
2020-01-31 16:12 ` sjpark
2020-01-31 16:55 ` Eric Dumazet
2020-01-31 17:05 ` sjpark
2020-01-31 17:08 ` Eric Dumazet
2020-01-31 15:10 ` Neal Cardwell
2020-01-31 18:12 ` Eric Dumazet
2020-01-31 22:11 ` Neal Cardwell
2020-01-31 22:17 ` SeongJae Park
2020-02-01 3:55 ` Neal Cardwell
2020-02-01 6:08 ` SeongJae Park [this message]
2020-02-01 13:30 ` Neal Cardwell
2020-01-31 22:53 ` Eric Dumazet
2020-02-03 15:40 ` David Laight
2020-02-03 15:54 ` Eric Dumazet
2020-01-31 12:24 ` [PATCH 3/3] selftests: net: Add FIN_ACK processing order related latency spike test sjpark
2020-01-31 14:56 ` Eric Dumazet
2020-01-31 15:13 ` sjpark
2020-01-31 14:00 ` [PATCH 0/3] Fix reconnection latency caused by FIN/ACK handling race David Laight
2020-01-31 15:05 ` sjpark
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