Colour me impressed: 2.6.25, kvm-69, virtio_net

[Freddie Cash <fjwcash@gmail.com>]

We've been using Xen 3.0 for the past 18-ish months on a couple boxes here 
and were quite impressed with it, especially when using the xen-tools 
package on Debian.  But, it couldn't run FreeBSD or Windows guests on our 
existing hardware, so we bought shiny new Opteron 2000-series systems 
with SVM support.  And then the problems began.

Xen 3.1/3.2 broke too many things for us (especially in the network 
setup), and we could not get a stable, working, reliable dom0 let alone 
any domUs.  Mainly due to our hardware requiring a newer Linux kernel 
than 2.6.18 (RAID controller and NIC weren't supported until 2.6.20).

So we started testing KVM, originally with kvm-60 and kernel 2.6.22 on 
Debian Lenny.  Since then, we've moved to kernel 2.6.24 and 2.6.25, along 
with kvm-69.  We've been running Windows XP, FreeBSD, and Debian guests 
for the past few months with very few problems.

Today, I managed to get a couple Linux guests to load using the virtio 
drivers in kernel 2.6.25.  Colour me impressed!

I thought the emulated e1000 interface had good performance:  the network 
throughput of virtio_net (as tested using iperf) is wire-speed.  I was 
able to saturate a gigabit link using iperf from a guest running with 
virtio_net!  Average throughput was 860+ Mbps, with highs around 980 
Mbps.

That, combined with how easy it is to manage kvm (I wrote my own 
management scripts and config file format that is a lot easier to read 
than the Xen ones), configure networking in the host (done using the 
distro tools, not some arcane python scripts), and get hardware driver 
support in the host (standard distro kernels, not ancient xen-specific 
ones), makes it very hard to find reasons to run Xen.  The only reason I 
can find, is if you have hardware that doesn't support VMX/SVM, but is 
supported by kernel 2.6.18, in which case Xen 3.0 works quite nicely (not 
3.1 or later).

Kudos to the kvm devs, the kernel devs, the qemu devs, and the rest who 
are involved in making KVM work so well!

For those interested, I've put some iperf results into the KVM Wiki 
(http://kvm.qumranet.com/kvmwiki/Using_VirtIO_NIC), along with info on 
the management scripts/config file format I use 
(http://kvm.qumranet.com/kvmwiki/HowToConfigScript).

Now, if only the FreeBSD port of KVM could be completed, so we could use 
ZFS in the host instead of LVM.  ;)

-- 
Freddie Cash
fjwcash@gmail.com