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Date:      Sat, 9 Aug 2014 22:06:46 -0700
From:      John-Mark Gurney <jmg@funkthat.com>
To:        Niu Zhixiong <kaiaixi@gmail.com>
Cc:        Michael Tuexen <Michael.Tuexen@lurchi.franken.de>, Bill Yuan <bycn82@gmail.com>, freebsd-net@freebsd.org
Subject:   Re: A problem on TCP in High RTT Environment.
Message-ID:  <20140810050646.GN83475@funkthat.com>
In-Reply-To: <CAOENNMDgcQoT3T4ayu3fK7YJs178ACH_2y5b4SvPhkwR3o_4Hw@mail.gmail.com>
References:  <8AE1AC56-D52F-4F13-AAA3-BB96042B37DD@lurchi.franken.de> <20140809204500.GG83475@funkthat.com> <3F6BC212-4223-4AAC-8668-A27075DC55C2@lurchi.franken.de> <CAOENNMCPuiYS7LHwMfOczhZ4yisjGkpOmWzv2pcAoi9Hhzb7dw@mail.gmail.com> <20140810022350.GI83475@funkthat.com> <CAOENNMB3=FZx5kSHVPDPBTtMKbmYJ=c_XNMcuYuoLPe=6U%2Bkxg@mail.gmail.com> <CAOENNMARg36KH1Y%2B0wG8pd7sSf8XKnMf6g790_KiKaj3Mdwyjw@mail.gmail.com> <20140810033212.GL83475@funkthat.com> <CAOENNMA-dwPQr53bM4rzC=1eitoi-JAB4mCGx4zybFwUC=GMNg@mail.gmail.com> <CAOENNMDgcQoT3T4ayu3fK7YJs178ACH_2y5b4SvPhkwR3o_4Hw@mail.gmail.com>

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Niu Zhixiong wrote this message on Sun, Aug 10, 2014 at 11:56 +0800:
> Actually. In the
> http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/configtuning-kernel-limits.html
> 12.11.2.2. TCP Bandwidth Delay Product
> I saw an option called
> net.inet.tcp.inflight.enable
> net.inet.tcp.inflight.debug
> net.inet.tcp.inflight.min
> 
> But, in FreeBSD 9.3R and 10R. I cannot find anything related to inflight in
> sysctl net.inet.tcp.

Looks like it was removed for the pluggable congestion control:
https://svnweb.freebsd.org/changeset/base/r211315

man mod_cc for more info...

> On Sun, Aug 10, 2014 at 11:48 AM, Niu Zhixiong <kaiaixi@gmail.com> wrote:
> 
> > I am using Intel I350-T4 NIC. The LRO is closed by default. And by the
> > way, when I am using KVM-based virtual machine(virtio NIC) do the exactly
> > same test. The results are same.
> >
> > ifconfig igb0
> > igb0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
> >
> > options=403bb<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,TSO4,TSO6,VLAN_HWTSO>
> >  ether a0:36:9f:38:27:d0
> > inet 10.0.10.3 netmask 0xffffff00 broadcast 10.0.10.255
> > inet6 fe80::a236:9fff:fe38:27d0%igb0 prefixlen 64 scopeid 0x1
> >  nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
> > media: Ethernet autoselect (1000baseT <full-duplex>)
> >  status: active
> >
> > Regards,
> > Niu Zhixiong
> > ?????????????????????????????????????????????
> >  kaiaixi@gmail.com
> >
> >
> > On Sun, Aug 10, 2014 at 11:32 AM, John-Mark Gurney <jmg@funkthat.com>
> > wrote:
> >
> >> Niu Zhixiong wrote this message on Sun, Aug 10, 2014 at 10:50 +0800:
> >> > I am sorry that I upload a WRONG SCTP capture. But, the throughput is
> >> same.
> >> > SCTP is double than TCP, about 18Mbps.
> >> > ???
> >> >  sctp_2.pcapng.gz
> >> > <
> >> https://docs.google.com/file/d/0By8sTL79ob4tMlh4WDlTSndHX0k/edit?usp=drive_web
> >> >
> >> > ???
> >>
> >> Ok, the owin graph is very interesting...  We do have a full 2MB window
> >> on the receiver side, but for some reason, we only ever have just under
> >> 6k outstanding on the connection...
> >>
> >> So, it looks like we send for a short period of time, and then stop
> >> sending...  Do you have LRO enabled?  I think it might be related to:
> >> https://svnweb.freebsd.org/changeset/base/r256920
> >>
> >> As I'm seeing >100ms gaps where the sender doesn't send any data, and
> >> as soon as more than one ack comes in, the next segment goes out...  If
> >> we only receive a single ack, then we wait for a timeout before sending
> >> the next segment..
> >>
> >> Can you try to disable LRO on the receiving host?
> >>
> >> ifconfig <iface> -lro
> >>
> >> And see if that helps... If it does...  Applying the patch, or compiling
> >> a more recent kernel from stable/10 that is after r257367 as that is was
> >> the date that the change was merged...
> >>
> >> > On Sun, Aug 10, 2014 at 10:42 AM, Niu Zhixiong <kaiaixi@gmail.com>
> >> wrote:
> >> >
> >> > > I am sure that wnd is about 2MB all the time.
> >> > > This is my latest capture, plz see Google Drive.
> >> > > In the latest test, TCP(0s-120s) is about 9Mbps and SCTP(0s-120s) is
> >> about
> >> > > 18Mbps.
> >> > > (The bandwidth(20Mbps) and delay(200ms) is set by dummynet)
> >> > > The SCTP and TCP are tested in same environment.
> >> > >
> >> > > ???
> >> > >  sctp.pcapng.gz
> >> > > <
> >> https://docs.google.com/file/d/0By8sTL79ob4tYl9sM2V5a19iNVU/edit?usp=drive_web
> >> >
> >> > > ??????
> >> > >  tcp.pcapng.gz
> >> > > <
> >> https://docs.google.com/file/d/0By8sTL79ob4tV0NMR1FYLUQ3MWs/edit?usp=drive_web
> >> >
> >> > > ???
> >> > >
> >> > >
> >> > >
> >> > > Regards,
> >> > > Niu Zhixiong
> >> > > ?????????????????????????????????????????????
> >> > >  kaiaixi@gmail.com
> >> > >
> >> > >
> >> > > On Sun, Aug 10, 2014 at 10:23 AM, John-Mark Gurney <jmg@funkthat.com>
> >> > > wrote:
> >> > >
> >> > >> Niu Zhixiong wrote this message on Sun, Aug 10, 2014 at 10:12 +0800:
> >> > >> > During the TCP4 transmission.
> >> > >> > Proto Recv-Q Send-Q Local Address          Foreign Address
> >> > >>  (state)
> >> > >> > tcp4       0 2097346 10.0.10.2.13504        10.0.10.3.9000
> >> > >> > ESTABLISHED
> >> > >>
> >> > >> Ok, so you are getting a full 2MB in there, and w/ that, you should
> >> > >> easily be saturating your pipe...
> >> > >>
> >> > >> The next thing would be to get a tcpdump, and take a look at the
> >> > >> window size.. Wireshark has lots of neat tools to make this analysis
> >> > >> easy...  Another tool that is good is tcptrace..  It can output a
> >> > >> variety of different graphs that will help you track down, and see
> >> > >> what part of the system is the problem...
> >> > >>
> >> > >> You probably only need a few tens of seconds of the tcpdump...
> >> > >>
> >> > >> > On Sun, Aug 10, 2014 at 4:58 AM, Michael Tuexen <
> >> > >> > Michael.Tuexen@lurchi.franken.de> wrote:
> >> > >> >
> >> > >> > >
> >> > >> > > On 09 Aug 2014, at 22:45, John-Mark Gurney <jmg@funkthat.com>
> >> wrote:
> >> > >> > >
> >> > >> > > > Michael Tuexen wrote this message on Sat, Aug 09, 2014 at 21:51
> >> > >> +0200:
> >> > >> > > >>
> >> > >> > > >> On 09 Aug 2014, at 20:42, John-Mark Gurney <jmg@funkthat.com>
> >> > >> wrote:
> >> > >> > > >>
> >> > >> > > >>> Niu Zhixiong wrote this message on Fri, Aug 08, 2014 at 20:34
> >> > >> +0800:
> >> > >> > > >>>> Dear all,
> >> > >> > > >>>>
> >> > >> > > >>>> Last month, I send problems related to FTP/TCP in a high RTT
> >> > >> > > environment.
> >> > >> > > >>>> After that, I setup a simulation environment(Dummynet) to
> >> test
> >> > >> TCP
> >> > >> > > and SCTP
> >> > >> > > >>>> in high delay environment. After finishing the test, I can
> >> see
> >> > >> TCP is
> >> > >> > > >>>> always slower than SCTP. But, I think it is not possible.
> >> (Plz
> >> > >> see the
> >> > >> > > >>>> figure in the attachment). When the delay is 200ms(means
> >> > >> RTT=400ms).
> >> > >> > > >>>> Besides, the TCP is extremely slow.
> >> > >> > > >>>>
> >> > >> > > >>>> ALL BW=20Mbps, DELAY= 0 ~ 200MS, Packet LOSS = 0 (by
> >> dummynet)
> >> > >> > > >>>>
> >> > >> > > >>>> This is my parameters:
> >> > >> > > >>>> FreeBSD vfreetest0 10.0-RELEASE FreeBSD 10.0-RELEASE #0:
> >> Thu Aug
> >> > >>  7
> >> > >> > > >>>> 11:04:15 HKT 2014
> >> > >> > > >>>>
> >> > >> > > >>>> sysctl net.inet.tcp
> >> > >> > > >>>
> >> > >> > > >>> [...]
> >> > >> > > >>>
> >> > >> > > >>>> net.inet.tcp.recvbuf_auto: 0
> >> > >> > > >>>
> >> > >> > > >>> [...]
> >> > >> > > >>>
> >> > >> > > >>>> net.inet.tcp.sendbuf_auto: 0
> >> > >> > > >>>
> >> > >> > > >>> Try enabling this...  This should allow the buffer to grow
> >> large
> >> > >> enough
> >> > >> > > >>> to deal w/ the higher latency...
> >> > >> > > >>>
> >> > >> > > >>> Also, make sure your program isn't setting the recv buffer
> >> size
> >> > >> as that
> >> > >> > > >>> will disable the auto growing...
> >> > >> > > >> I think the program sets the buffer to 2MB, which it also
> >> does for
> >> > >> SCTP.
> >> > >> > > >> So having both statically at the same size makes sense for the
> >> > >> > > comparison.
> >> > >> > > >> I remember that there was a bug in the combination of LRO and
> >> > >> delayed
> >> > >> > > ACK,
> >> > >> > > >> which was fixed, but I don't remember it was fixed before
> >> 10.0...
> >> > >> > > >
> >> > >> > > > Sounds like disabling LRO and TSO would be a useful test to
> >> see if
> >> > >> that
> >> > >> > > > improves things...  But hiren said that the fix made it, so...
> >> > >> > > >
> >> > >> > > >>> If you use netstat -a, you should be able to see the send-q
> >> on the
> >> > >> > > >>> sender grow as necessary...
> >> > >> > > >
> >> > >> > > > Also, getting the send-q output while it's running would let
> >> us know
> >> > >> > > > if the buffer is getting to 2MB or not...
> >> > >> > > That is correct. Niu: Can you provide this?
> >>
> >> --
> >>   John-Mark Gurney                              Voice: +1 415 225 5579
> >>
> >>      "All that I will do, has been done, All that I have, has not."
> >>
> >
> >

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."



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