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Re: [Xen-users] Xen Performance

On Sat, Oct 17, 2009 at 2:19 AM, Grant McWilliams
<grantmasterflash@xxxxxxxxx> wrote:

> However a PV on Xen should
> cream KVM in just about every other aspect.

One of the reasons for pv_ops support in Linux kernel was that so when
the kernel runs in virtualization solutions (KVM, Xen, VMware, etc) it
can automatically switch and use virtualization-friendly instructions,
thus eliminating CPU overhead imposed by hardware-assisted
virtualization, achieving similar performance to that of Xen PV guest.
At least in theory :)

> I've heard and I haven't
> finished my testing yet to confirm this that KVM is faster than a Xen HVM
> doing the same tasks if they both have PV drivers which means KVM may be
> better solution for virtualizing Windows.

Do share your test results once you have them.

> I have a contract for Virtualizing
> 75 Window 2K systems

Are they even supported? Mainstream support ended many years ago.

> so I'll be doing a great deal of testing in the coming
> months to know for sure.

GPLPV does not support Windows 2000 anymore, so it'd be interesting to
see how you can work out I/O performance problems. Does HVM have PV
drivers for Windows 2000?

> However, it's getting harder all the time to
> stick with Xen because most distributions are dropping it.

RHEL5 is still supported until 2014, so it should cover existing installations.
I'm still having doubts about what to use for new installations in the
next year or two, but considering that (on my tests) 2.6.18-xen kernel
still outperforms forward-ported or pv_ops kernel I'd probably stick
with RHEL5.

> I'm now using
> Debian Lenny kernels in my Ubuntu DomUs.

tried that, had some problems, switched to self-compiled 2.6.29-xen
kernel. I'd rather not use pv_ops kernel (for now) since it doesn't
support growing memory beyond initial allocation (yet). Might take a
look at sid's kernel later though.

> It may end up being only Suse that
> supports Xen at some point. I think Xen is a great product but if KVM can
> manage to do the same thing and be easier to manage Xen will sadly go away.
> I've sort of given up hope that it will ever have decent Dom0 support in the
> kernel. By the time that happens KVM will have taken over the entire Linux
> VM world (which makes the conspiracy theory part of my brain buzz).

I was actually thinking that the best OS for Xen dom0 in the future
might be Solaris 11 :D
Assuming Oracle doesn't kill xVM, that is.


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