netdev - Re: resend: tcp: performance issue with fastopen connections (mss

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Date:   Fri, 13 Jan 2017 12:32:53 -0500
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Alexey Kodanev <alexey.kodanev@...cle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Vasily Isaenko <vasily.isaenko@...cle.com>,
        Yuchung Cheng <ycheng@...gle.com>
Subject: Re: resend: tcp: performance issue with fastopen connections (mss > window)

On Fri, Jan 13, 2017 at 12:14 PM, Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Fri, Jan 13, 2017 at 9:07 AM, Alexey Kodanev
> <alexey.kodanev@...cle.com> wrote:
> > Hi Eric,
> > On 13.01.2017 18:35, Eric Dumazet wrote:
>
> >> Care to send a packetdrill test so that we have a clear picture of what
> >> is going on ?
> >
> > Is it capable of making two connections in the single test, one after
> > another?
>
> Absolutely.
>
> Neal, Yuchung would you be kind enough to send a Fastopen tpacketdrill
> template showing a typical fastopen test
> running on an upstream kernel ?
>
> Thanks !

Sure, here is an example packetdrill script, IIRC written by Yuchung,
which demonstrates TCP fast open and consecutive active connections:

`sysctl -q net.ipv4.tcp_timestamps=0`

// Cache warmup: send a Fast Open cookie request
0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
   +0 sendto(3, ..., 0, MSG_FASTOPEN, ..., ...) = -1 EINPROGRESS
(Operation is now in progress)
   +0 > S 0:0(0) <mss 1460,nop,nop,sackOK,nop,wscale 8,FO,nop,nop>
+.010 < S. 123:123(0) ack 1 win 5840 <mss
1040,nop,nop,sackOK,nop,wscale 6,FO abcd1234,nop,nop>
   +0 > . 1:1(0) ack 1
   +0 close(3) = 0
   +0 > F. 1:1(0) ack 1
+.010 < F. 1:1(0) ack 2 win 92
   +0 > .  2:2(0) ack 2

//
// TEST1: Servers sends SYN-ACK with data and another two data packets
//
   +0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 4
   +0 fcntl(4, F_SETFL, O_RDWR|O_NONBLOCK) = 0
   +0 sendto(4, ..., 1000, MSG_FASTOPEN, ..., ...) = 1000
   +0 > S 0:1000(1000) <mss 1460,nop,nop,sackOK,nop,wscale 8,FO
abcd1234,nop,nop>
+.010 < S. 1000000:1001400(1400) ack 1001 win 5840 <mss
1040,nop,nop,sackOK,nop,wscale 6>
   +0 < . 1401:2801(1400) ack 1001 win 257
   +0 < P. 2801:3001(200) ack 1001 win 257

neal