

Why Bytemark didn't use Xen - ichilton
http://blog.bytemark.co.uk//2011/02/28/why-we-skipped-xen

======
blocke
Xen was a standalone hypervisor that run under the Linux kernel. It was
developed independently of Linux. Linux was a guest along for the ride.

With KVM the hypervisor is over the Linux kernel and gets to use the
facilities of the host kernel. Less code, less complexity. Why wouldn't Linux
kernel hackers prefer KVM over Xen? They get full control (aka the ability to
get crap fixed without hounding an external party) and get to reuse code they
already have to write anyway.

Preferring the KVM approach over Xen makes 100% sense to me in the long term
for the Linux folks.

------
anonymous246
Xen is a classic example of a technology and company that never reached its
full market potential due to nerd pride.

In this particular case, Redhat/Linus/kernel hacker's obstinate refusal to add
it to the stock kernel. They exhibited NIH and did KVM (which surprise
surprise was owned by Redhat). I'm no virtualization expert, but KVM is doing
things totally different than everybody else (no hypervisor), and I'm not 100%
sure that KVM's way is better.

Xen should be a cautionary tale for startups that opening source is not a
silver bullet. The capricious behavior of a coterie can kill you even if that
coterie is ostensiby not controlled by any company.

~~~
viraptor
I'm not sure you're about some things you wrote. "nerd pride"? Really?

> In this particular case, Redhat/Linus/kernel hacker's obstinate refusal to
> add it to the stock kernel.

Why obstinate? Xen is not a part of a kernel in some ways. Some capabilities
of the system have to be maintained in parallel in both the hypervisor and
kernel. And it's not like it was rejected because it was a VM solution -
another one was proposed and accepted into mainline (KVM).

> They exhibited NIH and did KVM (which surprise surprise was owned by
> Redhat).

LKML has a lot of talk about "why"... it wasn't simply NIH. Regarding "owned
by Redhat" - it was included first, then owned by RH:

* "The Linux kernel 2.6.20 release (February 2007) was the first to include KVM." (wikipedia)

* "In September 2008, Red Hat announced the acquisition of Qumranet, Inc. The acquisition included Qumranet's virtualization solutions, including its KVM (Kernel Virtual Machine) platform" (<http://www.redhat.com/promo/qumranet/>)

> KVM is doing things totally different than everybody else (no hypervisor),
> and I'm not 100% sure that KVM's way is better.

KVM relies on the idea that if the current kernel already does the work, why
duplicate the effort? Apart from minimal, verifiable hypervisors idea not
being possible... what are your actual objections?

I'm not saying KVM is better / worse here... but let's cut the FUD at least.

~~~
anonymous246
I stand corrected wrt Redhat's ownership of KVM. Thanks for the clarification.

I re-read some more web pages in the light of your comments, and I remain
unconvinced that nerd pride wasn't at the root of the Linux kernel devs
dismissal of Xen. It's happened before (Con Kolivas's patches for instance),
so I don't think I'm saying anything radical.

IIRC, the hypervisor technology is the standard way to do virtualization since
the mainframe days. I haven't heard anything remarkable about KVM to convince
me that their hypervisor-less architecture is better.

~~~
viraptor
Re. stuff like Con Kolivas, etc. I recommend listening to this talk:
[http://mirrors.dotsrc.org/fosdem/2011/maintracks/kernel-
deve...](http://mirrors.dotsrc.org/fosdem/2011/maintracks/kernel-
development.xvid.avi) \- it gives some real-live perspective on issues of not-
accepted modules.

