-enable-kvm - can it be a required option?

-enable-kvm - can it be a required option?

[Michael Tokarev]

What I mean is: if asked to enable kvm but kvm
can't be initialized for some reason (lack of
virt extensions on the cpu, permission denied
and so on), can we stop with a fatal error
instead of continuing in emulated mode?

Or maybe with another option, like -require-kvm?

I understand that -enable-kvm is now in upstream
qemu too, and _there_ it means something different,
that is, it enables something that is disabled by
default.  But even with that, if user asks for
something and that something isn't available, it
seems like a good idea to stop here instead of
producing a warning and continuing...

This is especially true for kvm where -enable-kvm
is the default anyway.

I see more and more people are using this option
now in a hope that kvm will actually stop when
no virt extensions are available.  It was my
first reaction too, "wow, now I can force it to
require kvm extensions instead of running 1000
times slower!".  So this has something to think
about, it looks like... ;)

Thanks!

/mjt

Re: -enable-kvm - can it be a required option?

[Anthony Liguori]

On 03/17/2010 03:18 PM, Michael Tokarev wrote:
> What I mean is: if asked to enable kvm but kvm
> can't be initialized for some reason (lack of
> virt extensions on the cpu, permission denied
> and so on), can we stop with a fatal error
> instead of continuing in emulated mode?
>    

What I've been thinking, is that we should make kvm enablement a -cpu 
option.  Something like:

-cpu host,accel=kvm
-cpu host,accel=tcg
-cpu host,accel=kvm:tcg

(1) would be KVM only, (2) would be TCG only, (3) would be KVM falling 
back to TCG.

What's nice about this approach, is that we already pull CPU model 
definitions from a global config file which means that you could tweak 
this parameter to your liking.

Regards,

Anthony Liguori