Re: [Qemu-devel] [PATCH] i386: Support "-cpu host" on TCG too

[Eduardo Habkost <ehabkost@redhat.com>]

On Thu, Jan 19, 2017 at 06:22:40PM +0000, Peter Maydell wrote:
> On 19 January 2017 at 17:50, Daniel P. Berrange <berrange@redhat.com> wrote:
> > On Mon, Jan 16, 2017 at 05:54:52PM -0200, Eduardo Habkost wrote:
> >> Change the meaning of "-cpu host" to "enable all features
> >> supported by the accelerator in the current host", so that it can
> >> be used to enable/query all features supported by TCG.
> >>
> >> To make sure "host" is still at the end of the list in "-cpu
> >> help", add a "ordering" field that will be used when sorting the
> >> CPU model list.
> >
> > To be clear, "-cpu host" for TCG is not talking about the actual
> > host OS feature support, right ? x86_64 TCG can be run on a ppc host,
> > so presumably "-cpu host" just means "all features that this TCG binary
> > is able to emulate" ?
> >
> > This feels like it is introducing scope for confusion vs KVM -cpu host,
> > so I wonder if different naming is better for this.
> 
> The idea is that you do want an option that works whatever the
> accelerator is, though, so as a user you don't need to worry
> about messing with the command line for KVM vs TCG vs "try
> KVM and fall back to TCG". (I think "-cpu best" has been thrown about
> as a suggestion for this before.)

"-cpu best" has been proposed with different semantics before:
one meant "select the the best CPU model from the builtin table",
and another that's equivalent to the meaning of "host" in this
patch.

s390x uses "max CPU model" internally to represent a CPU model
that has all supported features enabled.

If "-cpu host" is not a good name, I suggest "-cpu max".

-- 
Eduardo