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Date: Tue, 16 Nov 2010 11:20:50 -0600
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [PATCH] Introduce -accel command option.
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To: Alexander Graf <agraf@suse.de>
Cc: Anthony PERARD <anthony.perard@citrix.com>, QEMU-devel <qemu-devel@nongnu.org>

On 11/16/2010 10:59 AM, Alexander Graf wrote:
>
>> Surely, only if it is running on a Xen Dom0. If you use -M xenpv on a KVM
>> host, then -M xenpv should imply -machine accel=kvm (ie it would be using
>> xenner)
>>      
> Actually, it should imply -machine accel=kvm,tcg :). Accelerators really are not a machine property. In an ideal world, -M pc would just work with xen hvm if -accel xen is given.
>    

No, an accelerator is both a CPU selection and a machine 
characteristic.  For KVM, we overload -cpu to modify both the KVM CPU 
and the TCG CPU both this won't work with accel=xen.  We probably 
shouldn't do this with KVM either because there's a significant 
different between trying to do cpuid masking with KVM and modifying the 
TCG cpu emulation support.

Both KVM and Xen have other impacts on the platform devices though.  KVM 
does not support SMM so it disables that in the i440fx.  KVM prefers to 
use it's own in-kernel local APIC (and IOAPIC).  That makes it a 
property of the machine.

Regards,

Anthony Liguori

> Alex
>
>