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

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

[Bharata B Rao]

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.

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

[Eduardo Habkost]

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.

-- 
Eduardo

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

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

[Andrea Bolognani]

On Wed, 2016-08-10 at 20:11 +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 filed bugs for this yesterday:

  https://bugzilla.redhat.com/1365643 (QEMU)
  https://bugzilla.redhat.com/1365647 (libvirt)

libvirt could certainly be adapted to use -global, but that
would not benefit people running QEMU directly, or driving
QEMU 2.7 with any existing libvirt version.

Plus, it would not solve the issue with CPU models that
include a dot in their names, as you already noted.

I won't comment on the patches because I'm not qualified to :)

But, assuming they both restore the previous behaviour,
getting either one into 2.7 would definitely be great.

-- 
Andrea Bolognani / Red Hat / Virtualization