Date: Sat, 9 Aug 2014 19:23:50 -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: <20140810022350.GI83475@funkthat.com> In-Reply-To: <CAOENNMCPuiYS7LHwMfOczhZ4yisjGkpOmWzv2pcAoi9Hhzb7dw@mail.gmail.com> References: <CAOENNMA_CiBDJc0kchzUbTcf_JBwTJPF=PdBAUB6FPo-KzYkeQ@mail.gmail.com> <20140809184232.GF83475@funkthat.com> <8AE1AC56-D52F-4F13-AAA3-BB96042B37DD@lurchi.franken.de> <20140809204500.GG83475@funkthat.com> <3F6BC212-4223-4AAC-8668-A27075DC55C2@lurchi.franken.de> <CAOENNMCPuiYS7LHwMfOczhZ4yisjGkpOmWzv2pcAoi9Hhzb7dw@mail.gmail.com>
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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."
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