A problem on TCP in High RTT Environment.

Sun Aug 10 03:56:08 UTC 2014

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.

Regards,
Niu Zhixiong
－－－－－－－－－－－－－－－
 kaiaixi at gmail.com

On Sun, Aug 10, 2014 at 11:48 AM, Niu Zhixiong <kaiaixi at 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 at gmail.com
>
>
> On Sun, Aug 10, 2014 at 11:32 AM, John-Mark Gurney <jmg at 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 at 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 at gmail.com
>> > >
>> > >
>> > > On Sun, Aug 10, 2014 at 10:23 AM, John-Mark Gurney <jmg at 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 at lurchi.franken.de> wrote:
>> > >> >
>> > >> > >
>> > >> > > On 09 Aug 2014, at 22:45, John-Mark Gurney <jmg at 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 at 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."
>>
>
>