On 15 June 2017 at 17:17, Martin Kelly <mkelly@xevo.com> wrote:

> I am no expert, but running qemu -cpu help just says:
>
> kvm32 - "Common 32-bit KVM processor"
> kvm64 - "Common 64-bit KVM processor"
>
> My best guess is that, running on qemu without kvm, both cases will be
> slow (since it's all software emulation). But, using qemu -kvm, it should
> be fast as long as you run on a native CPU that is core2duo or better, as
> the native instructions can just be exposed and passed through to the host.
> Since core2duo is very old by now, it should be fast for virtually everyone
> building on x86.
>

Right, I did some digging.  Assuming you have KVM enabled then in the
general case the -cpu option is irrelevant as the instructions are handled
natively.  -cpu just changes what CPUID flags the userspace sees, and so
this is the Right Thing To Do.

Ross