From mboxrd@z Thu Jan 1 00:00:00 1970 From: Cherie Cheung Subject: Re: RE: [Xen-users] Network performance - sending from VM to VM using TCP Date: Sat, 28 May 2005 06:56:44 +0800 Message-ID: <4713f859050527155678a44e8a@mail.gmail.com> References: <8ae780250505270945d270a73@mail.gmail.com> Reply-To: Cherie Cheung Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <8ae780250505270945d270a73@mail.gmail.com> Content-Disposition: inline List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: bin.ren@cl.cam.ac.uk Cc: xen-devel@lists.xensource.com, xen-users@lists.xensource.com List-Id: xen-devel@lists.xenproject.org Bin, Thank you so much. I'll test that out to try to obtain these results. Cherie On 5/28/05, Bin Ren wrote: > Cherie: >=20 > I've tried to repeat the testing and here are the results: >=20 > Basic set up: xen machine runs latest xen-unstable and Debian sarge; > server runs latest Gentoo linux (native). both have intel e1000 mt > NICs and connect directly throught a 1Gbps switch. >=20 > (1) AFAIK, dummynet is for FreeBSD only, so I use the Linux kernel > network emulator module > (http://developer.osdl.org/shemminger/netem/index.html) and sets the > delay of server eth0 to 10ms using command 'tc qdisc add dev eth0 root > netem delay 10ms'. >=20 > (2) With linux kernel default networking settings, (i.e. no tcp > tuning): netperf -H server -l 30: >=20 > without delay, without tuning > dom0->server: 665Mbps > dom1->server: 490Mbps >=20 > with 10ms delay, without tuning > dom0->server: 82Mbps > dom1->server: 73Mbps >=20 > Note that *both* dom0 and dom1 show significant throughput drops. This > is different from what you've seen. >=20 > (3) Add linux tcp tuning > (http://www-didc.lbl.gov/TCP-tuning/linux.html), netperf -H server -l > 30: >=20 > without delay, with tuning > dom0->server: 654Mbps > dom1->server: 488Mbps >=20 > with 10ms delay, with tuning > dom0->server: 610Mbps > dom1->server: 480Mbps >=20 > Note: without delay, tuning doesn't provide gains in throughputs. > however, with delay, both dom0 and dom1 see only *slight* drop in > throughputs. This makes sense as linux tcp/ip stack needs tuning for > very long-fat pipes. In your case, 300Mbps + 80ms seems to emulate > transcontinental links. Still, YMMV. >=20 > - Bin >=20 > On 5/27/05, Ian Pratt wrote: > > > I have been simulating a network using dummynet and > > > evaluating it using netperf. Xen3.0-unstable is used and the > > > VMs are vmlinuz-2.6.11-xenU. The simulated link is 300Mbps > > > with 80ms RTT. > > > Using netperf, I sent data using TCP from domain-0 of machine > > > 1 to domain-0 of machine 2. Then I repeat the experiment, but > > > this time from VM-1 of machine 1 to VM-1 of machine 2. > > > > > > However, the performance across the two VMs is substantially > > > worse than that across domain-0. Here's the result: > > > > Someone else was having problems with low performance via dummynet a > > couple of months back. It's presumably dummynet's packet scheduling > > causing some bad interaction with the batch processing of packets in > > netfront/back. > > > > The first step to understanding this is probably to capture a tcpdump > > and look at it with tcptrace to see what's happening with window sizes > > and scheduling of packets. > > > > Ian > > > > _______________________________________________ > > Xen-devel mailing list > > Xen-devel@lists.xensource.com > > http://lists.xensource.com/xen-devel > > >