Re: RE: [Xen-users] Network performance - sending from VM to VM using TCP

[Cherie Cheung <ccyxen@gmail.com>]

Bin,

Thank you so much. I'll test that out to try to obtain these results.

Cherie

On 5/28/05, Bin Ren <bin.ren@gmail.com> wrote:
> Cherie:
> 
> I've tried to repeat the testing and here are the results:
> 
> 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.
> 
> (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'.
> 
> (2) With linux kernel default networking settings, (i.e. no tcp
> tuning): netperf -H server -l 30:
> 
> without delay, without tuning
> dom0->server: 665Mbps
> dom1->server: 490Mbps
> 
> with 10ms delay, without tuning
> dom0->server: 82Mbps
> dom1->server: 73Mbps
> 
> Note that *both* dom0 and dom1 show significant throughput drops. This
> is different from what you've seen.
> 
> (3) Add linux tcp tuning
> (http://www-didc.lbl.gov/TCP-tuning/linux.html), netperf -H server -l
> 30:
> 
> without delay, with tuning
> dom0->server: 654Mbps
> dom1->server: 488Mbps
> 
> with 10ms delay, with tuning
> dom0->server: 610Mbps
> dom1->server: 480Mbps
> 
> 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.
> 
> - Bin
> 
> On 5/27/05, Ian Pratt <m+Ian.Pratt@cl.cam.ac.uk> 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
> >
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> >
>