Re: [Qemu-devel] spapr: CPU compat option works only with -global for pseries-2.7

[Eduardo Habkost]

On Wed, Aug 10, 2016 at 11:52:12AM -0300, Eduardo Habkost wrote:
> On Wed, Aug 10, 2016 at 08:11:16PM +0530, Bharata B Rao wrote:
> > Hi,
> > 
> > With CPU core hotplug support in pseries-2.7, we will have to specify
> > the compat type using -global only as we don't yet take care of parsing
> > -cpu cputype,compat=.
> > 
> > There have been patches to support that:
> > 
> > sPAPR specific one: 
> > https://lists.nongnu.org/archive/html/qemu-devel/2016-06/msg07564.html
> > 
> > PPC generic one: 
> > https://lists.gnu.org/archive/html/qemu-devel/2016-07/msg02676.html
> > 
> > but the patch isn't upstream yet.
> > 
> > The result is that instead of specifying
> > 
> > -cpu host,compat=power7 for pseries-2.7, we will have to use
> > 
> > -cpu host -global driver=host-powerpc64-cpu,property=compat,value=power7
> > 
> > This behaviour is specific to pseries-2.7 and for earlier machine types
> > the original way of specifying compat with -cpu works.
> > 
> > Will this be a concern for libvirt ? Would it be difficult for libvirt to
> > switch to -global when generating QEMU cmdline for compat mode for 
> > pseries-2.7
> > machine.
> > 
> > Or, should we just include one of the above patches so that
> > -cpu cputype,compat= continues to work for peseries-2.7 ?
> 
> I believe we should include the generic PPC patch ("ppc: parse
> cpu features once") in 2.7.

Actually, see my reply to the generic patch: I believe we don't
need to change all machines in 2.7, but just spapr (that is
probably the only buggy case). The other machines still use
cpu_ppc_init()/cpu_generic_init() and should work normally.

-- 
Eduardo