Re: Looking at using KVM for embedded product

[Jan Kiszka <jan.kiszka@siemens.com>]

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Tom Shoes wrote:
> On Wed, Jun 23, 2010 at 3:16 AM, Jan Kiszka <jan.kiszka@siemens.com> wrote:
> 
> Thanks Jan for the response.
> 
>> Why 2.6.26, specifically if you seem to have no customized bits?
>> Starting with a pre-historic kernel for a new project is hardly ever a
>> good choice.
> 
>   We had picked up 2.6.26 1 1/2 years back and now there is requirement
> to add virtualization. Many of the other bits has been ported to this kernel
> and 3/4th tested. So moving to newer kernel will be difficult unless there
> is a pressing requirement and this might be from the answer from you
> and Avi.

The effort you may save by sticking with 2.6.26 can quickly be consumed
by troubles and limitations you may face with this old kernel. Better
make sure your local bits are clean and easily portable to recent
kernels version - or even push them upstream. And if you already have a
test suite for your specific scenarios, switching the target shouldn't
be that problematic.

> 
>>>          b.  Will latest KVM code from linux-kvm.org run on Linux kernel 2.6.26?
>> kvm-kmod builds down to 2.6.24, but it is likely only tested down to
>> 2.6.27. And you will miss quite a few relevant performance optimization
>> due to limitations of 2.6.26.
>>
> 
> Do you mean the the KVM community test build every KVM releases down to
> 2.6.24

Speaking of kvm-kmod: http://buildbot.kiszka.org/kvm-kmod/waterfall

> and do testing (may be a cursory one) of KVM functionality down to
> 2.6.27?

Testing of kvm-kmod is a bit less ambitious. This compat package is not
that broadly used compared to the KVM modules that ship with standard or
distribution kernels. There are tests performed against 2.6.27 and
2.6.32 hosts ATM, but anything else depends on community feedback.
Still, we didn't face much kvm-kmod-specific issues in the recent past,
specifically after its stabilization phases.

However, if you decide to upgrade your kernel anyway, I would suggest to
go with the included KVM support first, only pick kvm-kmod if there is a
good reason.

Jan

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