Re: [kvm-devel] [Qemu-devel] expose host CPU features to guests: Take 3

[Dan Kenigsberg]

On Tue, Sep 25, 2007 at 03:07:44PM +0200, Jocelyn Mayer wrote:
> > So, running qemu without any parameters would use host capabilities if
> > kvm is available and the default qemu cpu if not.  The -cpu option can
> > be used to override this if necessary.
> 
> Well, it may be needed to integrate the "-cpu host" option.
> But I think it's a really bad idea that running qemu without the -cpu
> option would not act the same on different host. When I want to test
> qemu with the same command line, I want it to behave exactly the same,
> whatever the host I'm running on, like any other tool. Think about gcc,
> for example, if you launch it without option, it compiles for a generic
> CPU. If you want to tune the generated code, even for the host you're
> running on, you have to use -mcpu/-march/-mtune. Using one command line
> always have gives the same result.
> Then, my opinion is that running qemu without any -cpu option should
> always use a default target.

Note that in "take 3" the default is indeed to expose the "basic"
default cpu features if no -cpu is specified. One must add -cpu host in
order to read and expose the host cpuid.