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Re: [Xen-users] who comes from kvm?

To: Javier Guerra Giraldez <javier@xxxxxxxxxxx>
Subject: Re: [Xen-users] who comes from kvm?
From: Iustin Pop <iusty@xxxxxxxxx>
Date: Mon, 14 Feb 2011 01:02:43 +0100
Cc: xen-users@xxxxxxxxxxxxxxxxxxx, Steve Sapovits <steves06@xxxxxxxxxxx>
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On Fri, Feb 11, 2011 at 10:34:47PM -0500, Javier Guerra Giraldez wrote:
> On Fri, Feb 11, 2011 at 12:24 PM, Steve Sapovits <steves06@xxxxxxxxxxx> wrote:
> > (Xen is a type 1, KVM is a type 2)
> that's not exact since KVM doesn't run 'on top of' the Linux kernel;
> it's part of the Linux kernel.  as such, it has the same 'bare metal'
> access to hardware as the rest of the kernel or the Xen hypervisor.

Unless my understanding is wrong, this is not true. The QEMU process
still needs to run, and still does runs code on behalf of the VM; yes,
CPU is not emulated, memory access is direct, but IIRC even my paravirt
drivers, some stuff still goes through QEMU/kvm.

> IMHO, the main difference is that Xen has its own scheduler and
> arbitration logic, while KVM reuses existing Linux code.  pro: it can
> be tuned to the specific case of handling VMs.  con: a little
> duplication of code

A strace on the qemu process shows that it does lots of stuff, so I
don't think the situation is as simple as you describe it.

Corrections welcome.


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