Re: [Xen-users] RHEL xen vs kvm

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Wed, Apr 21, 2010 at 11:42:31PM -0700, Grant McWilliams wrote:
>    On Wed, Apr 21, 2010 at 7:26 PM, Jeff Sturm <[1]jeff.sturm@xxxxxxxxxx>
>    wrote:
> 
>      Â
> 
>      In the end I don't know that we needed two hypervisors that are so
>      similar, but we have them.  It's going to come down to something like
>      choosing between Intel or AMD.  One might have a slight edge over the
>      other at any moment, or be somehow more elegant than the other, but both
>      are very capable and you can do a lot with them.
> 
>      Â
> 
>      Jeff
> 
>      Â
> 
>    At some point (and we're fast getting there) we'll be able to apply Linus'
>    quote about the kernel not mattering to hypervisors. About now the
>    hypervisor is starting to not matter and how you manage your VMs is the
>    real reason to choose which system you use.
> 
>    Currently I only use Paravirtualization because it's about as fast as bare
>    metal (databases are the worst for virtualization and mysqlbench shows
>    performance within 1% of bare metal) and if you set them up with their own
>    kernel inside the VM disk it looks and acts like a real Linux server. The
>    other mode with Xen is HVM which is full virtualization and is necessary
>    to virtualize Windows. KVM does a better job of this then Xen and is
>    faster for full virt. 
>

Do you have some benchmarks to prove KVM being faster than Xen HVM? 


> However KVM isn't as fast as Xen PV even with KVM PV
>    drivers. It all depends on what your needs are. If we go by the Xen summit
>    slides the future of Xen is in hybrid virtualization which uses hardware
>    virtualization for everything the hardware supports and then uses
>    paravirtualization for everything else. This will be the best of both
>    worlds (HVM and PV). I don't see KVM moving away from what it's doing
>    (using Qemu for a lot of stuff, Hardware VT and paravirtualized network
>    and disk drivers). How much of a difference this will make I'm not sure.
> 
>    Here's my thoughts.
>    If I were primarily virtualizing Windows I'd use KVM.

Why? Xen has both the GPLPV Windows drivers, and the binary WHQL Citrix Windows 
PV drivers available today.

>    If I were primarily virtualizing Linux I'd use Xen.
>    If I was using a bunch of old 3.4 Ghz Dual Core Xeons (I am) I'd use Xen.
>    If I was wanting to nest VMs I'd use AMD CPUs and KVM (for now).
>

Xen also now has patches to supported Nested virtualization on both Intel and 
AMD.
I bet this will end up in the Xen 4.1 development tree in upcoming weeks.

>    If I wanted the most pain free path to keeping my hypervisor updated I'd
>    use KVM.
>    If I was doing desktop virtualization (local login, not network logins)
>    I'd use KVM or VirtualBox
>    If I wanted the most tried and true enterprise hypervisor out there and
>    didn't want to use VMWARE then I'd use Xen. Citrix Xenserver, VirtualIron,
>    Sun SVM (one flavor), Oracle Virtual Machine and Amazon EC2 are all based
>    on Xen.
>    It might look like I lean toward KVM from this list but I still prefer Xen
>    in most cases because of category 2.
> 

There are a lot of options for Xen dom0 kernel nowadays.. although extra 
patching
or fetching the git tree is still needed.

http://wiki.xensource.com/xenwiki/XenDom0Kernels

-- Pasi


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