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

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

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 ?

Regards,
Bharata.