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Re: [Xen-users] XEN 4.3.1 network performance issue

On Fri, Dec 27, 2013 at 02:17:19PM +0200, NiX wrote:
> > On Tue, Dec 24, 2013 at 05:06:37PM +0200, NiX wrote:
> >> Hi. I am running a XEN VM in PV mode. This VM has four cores enabled. VM
> >> network config is as follows:
> >>
> >> vif = ["ip=,mac=XX:XX:XX:XX:XX:XX,bridge=br0,rate=100Mb/s"]
> >>
> >> Dom0 is dual XEON X5450 with 16GB of RAM.
> >>
> >> I can barely zmap at 10mbps ~ 12k packets/second on this VM
> >>
> >
> > My google-fu tells me that zmap sends out gigantic amount of TCP SYN
> > packets in its default configuration. It is possible the ring size
> > between frontend and backend is the bottleneck. Data copying from
> > frontend to backend might also be a problem.
> >
> > You can probably patch your Dom0 and DomU kernel with multi-page ring
> > support to see if it makes it better.
> >
> > Wei.
> >
> I was not able neither to exceed 10k packets/second with a lightweight
> equivalent software and netback/0 fully utilized one 3GHz core.

Hmm... You're using kthread-based netback. In your use case frontend is
likely to create interrupt storm for backend. Do you have breakdown of
CPU usage (sy, si etc)?

> Of course I had tweaked both host/vm network because the default limits
> somewhat cannot properly handle 10k or more packets/second due to the
> default 1k open files limit and so forth
> Well you know, basic users can manage with 1k packets and/or connections
> second but I am not a basic user ;) Is there any handy link on how to use
> multi-page ring feature. I am going to test that.

Oops I missed the CPU load in your previous email. In that case CPU was
already fully loaded so multi-page ring might not provide you much
benefit. Plus there's no convenient way to test it so I think it doesn't
worth your time. Sorry.

Just courious, do you have any figures on baremetal performs for zmap?


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