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

[Daniel P. Berrange]

On Thu, Jan 19, 2017 at 04:31:45PM -0200, Eduardo Habkost wrote:
> On Thu, Jan 19, 2017 at 06:22:40PM +0000, Peter Maydell wrote:
> > On 19 January 2017 at 17:50, Daniel P. Berrange <address@hidden> 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".

Yeah, I think "-cpu max" better describes the intended semantics for this
with TCG. I guess for KVM  -cpu host & -cpu max would be equivalent.

Regards,
Daniel
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