Re: [Qemu-devel] [PATCH] Introduce -accel command option.

[Anthony PERARD]

On Tue, 16 Nov 2010, Anthony Liguori wrote:

> On 11/16/2010 11:24 AM, Alexander Graf wrote:
> > On 16.11.2010, at 18:20, Anthony Liguori wrote:
> >
> >
> >> 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.
> >>
> > So you're saying the machine should define an accel mask of accels it 
> > supports?
> >
> > However all this ends up internally, giving the user an easy option to 
> > choose accels would still be nice. Users don't use -device or -machine. 
> > They want shortcuts :).
> >
>
> User's want things to just work.
>
> That's why -M xenpv should imply -machine accel=xen.

Actually, it works like that for qemu-xen, we just specify -M xenpv, and
we don't have any --enable-xen or other -accel xen.

> A user should never have to specify and accelerator option IMHO.

-- 
Anthony PERARD