Questions about relation between kernel version and KVM userspace version

Questions about relation between kernel version and KVM userspace version

[Kenni Lund]

Hi list

I've been wondering about something for a while: How does the version of the kernel module and the version of the KVM userspace relate? Eg. if you run with a newer 2.6.27-2.6.28 kernel with the modules included, will you then benefit from using the modules from the latest KVM release together with the latest KVM userspace, or isn't it worth the effort?

According to http://kvm.qumranet.com/kvmwiki/Downloads, it is required to use at least kernel 2.6.25 to run KVM userspace 76 or newer. Does this mean that no changes/bugfixes has been made to the KVM kernel module since 2.6.25? Or is it because all the major bugfixes are made in KVM userspace instead of the KVM kernel modules?

And one last thing: When I compile the latest KVM modules from sourceforge, I'll be able to see the KVM module version in /var/log/messages when I load the module. But this isn't the case when I load the modules that comes with the kernel - how can I see check the KVM module version of the current kernel? modinfo etc. doesn't give out any information.

Thank you in advance...

Best Regards
Kenni

Re: Questions about relation between kernel version and KVM userspace version

[Sheng Yang]

On Friday 23 January 2009 07:47:23 Kenni Lund wrote:
> Hi list
>

Hi Kenni

> I've been wondering about something for a while: How does the version of
> the kernel module and the version of the KVM userspace relate? Eg. if you
> run with a newer 2.6.27-2.6.28 kernel with the modules included, will you
> then benefit from using the modules from the latest KVM release together
> with the latest KVM userspace, or isn't it worth the effort?
>
> According to http://kvm.qumranet.com/kvmwiki/Downloads, it is required to
> use at least kernel 2.6.25 to run KVM userspace 76 or newer. Does this mean
> that no changes/bugfixes has been made to the KVM kernel module since
> 2.6.25? Or is it because all the major bugfixes are made in KVM userspace
> instead of the KVM kernel modules?

Three factors here: Host Linux version you are using, KVM modules, KVM 
userspace. The released package you saw contained both KVM modules and KVM 
userspace. You would find latest KVM modules files in /kernel directory. 
That's the modules we meant to use.

And please use latest KVM release. Even Linux upstream is new, the latest KVM 
is newer. If you know how Linux kernel accept patches, you would know the 
upstream only accept new features when merge window is opening(and the 
maintainers are more careful with Linux upstream, so maybe not all new 
features can be pushed to Linux upstream). So every sub system of Linux kernel 
would hold lots of patches during merge window closed period. That's why 
latest KVM is newer.
>
> And one last thing: When I compile the latest KVM modules from sourceforge,
> I'll be able to see the KVM module version in /var/log/messages when I load
> the module. But this isn't the case when I load the modules that comes with
> the kernel - how can I see check the KVM module version of the current
> kernel? modinfo etc. doesn't give out any information.

Yeah, it have been replaced by KVM module in kvm-userspace, which is correct. 
I am afraid no version for Linux upstream would show. Versions are only tags 
applied on KVM upstream, no such things for kernel. And ensure you are using 
latest KVM release would make keep you sync with the community and happy. :)

-- 
regards
Yang, Sheng

Re: Questions about relation between kernel version and KVM userspace version

[Mark McLoughlin]

On Fri, 2009-01-23 at 00:47 +0100, Kenni Lund wrote:

>  I've been wondering about something for a while: How does the version
> of the kernel module and the version of the KVM userspace relate? Eg.
> if you run with a newer 2.6.27-2.6.28 kernel with the modules
> included, will you then benefit from using the modules from the latest
> KVM release together with the latest KVM userspace, or isn't it worth
> the effort?

There are a number of ways of thinking about this:

  * if you want to help out with KVM development and testing, using the
    latest released kvm.ko with your currently installed kernel might be
    a good idea. If you want to get really hard-core, use Avi's kernel
    git tree.

  * if you just want some KVM feature that isn't in your currently 
    installed kernel, the latest released kvm.ko might make sense.

  * if your main concern is stability, use an unmodified kernel release
    and stable updates - e.g. 2.6.27.x or 2.6.28.x

Which version of kvm-userspace/qemu you use is a very different story -
unless you have a very old kernel version, just use the latest release
kvm/qemu release.

Cheers,
Mark.