Date: Sat, 9 Aug 2014 22:58:25 +0200 From: Michael Tuexen <Michael.Tuexen@lurchi.franken.de> To: John-Mark Gurney <jmg@funkthat.com> Cc: freebsd-net@freebsd.org, Niu Zhixiong <kaiaixi@gmail.com>, Bill Yuan <bycn82@gmail.com> Subject: Re: A problem on TCP in High RTT Environment. Message-ID: <3F6BC212-4223-4AAC-8668-A27075DC55C2@lurchi.franken.de> In-Reply-To: <20140809204500.GG83475@funkthat.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>
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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? Best regards Michael > > -- > 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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