[Dev] Build server Xen vs KVM
Luke Shumaker
lukeshu at lukeshu.com
Tue Nov 7 02:35:51 GMT 2017
On Mon, 06 Nov 2017 20:21:28 -0500,
Josh Branning wrote:
> On 07/11/17 01:19, Luke Shumaker wrote:
> > Hi all,
> >
> > In the original email, I had said that I planned on using Xen on the
> > build server. I suppose I should ask though: Does anyone have a
> > strong opinion on KVM vs Xen?
> >
> > (Just waiting on the the mobo now. Also, my RAM seller had
> > mis-counted his inventory, and so I'm only getting 16GB in this
> > order).
> >
>
> KVM, built into kernel. Last time I checked Xen required lots of
> dependencies.
KVM is a mechanism built into the kernel, but you still need external
(userspace) programs to do everything but CPU virtualization; which
probably means QEMU.
The dependency lists of QEMU and Xen aren't that different.
(NB: much Xen's para-virtualized device code comes from QEMU)
> Other question to consider is the overhead added as it's a build
> server, but if it's para-visualization shouldn't be so much of a
> problem.
Both KVM and Xen will be using HVM for CPU virtualization these days
(well, KVM always used HVM; Xen used to use para-virtualization for
CPU though); the real overhead will be with devices.
Both KVM/QEMU and Xen should be using virtio (para-virtualization) for
most devices. I don't know what KVM/QEMU's para-virtualized devices
story is like these days.
One thing to note, while KVM can hot-plug add more CPUs, Xen has
support for hot-plugging and unplugging them. I said that 16 of the
CPU cores would be dedicated to the build server VM, but Xen would
give the possiblity to rig up a system to allow "ballooning" the
number of cores up to 31 (I'd keep one reserved for dom0) if other VMs
are inactive.
--
Happy hacking,
~ Luke Shumaker
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