Re: [PATCH v16 08/11] qapi/s390x/cpu topology: set-cpu-topology monitor command

[Pierre Morel]

On 2/27/23 13:15, Nina Schoetterl-Glausch wrote:
> On Mon, 2023-02-27 at 11:57 +0100, Pierre Morel wrote:
> > On 2/24/23 18:15, Nina Schoetterl-Glausch wrote:
> > > On Wed, 2023-02-22 at 15:21 +0100, Pierre Morel wrote:
> > > > The modification of the CPU attributes are done through a monitor
> > > > command.
> > > >
> > > > It allows to move the core inside the topology tree to optimize
> > > > the cache usage in the case the host's hypervisor previously
> > > > moved the CPU.
> > > >
> > > > The same command allows to modify the CPU attributes modifiers
> > > > like polarization entitlement and the dedicated attribute to notify
> > > > the guest if the host admin modified scheduling or dedication of a vCPU.
> > > >
> > > > With this knowledge the guest has the possibility to optimize the
> > > > usage of the vCPUs.
> > > >
> > > > The command has a feature unstable for the moment.
> > > >
> > > > Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> > > > ---
> > > >    qapi/machine-target.json |  35 +++++++++
> > > >    include/monitor/hmp.h    |   1 +
> > > >    hw/s390x/cpu-topology.c  | 154 +++++++++++++++++++++++++++++++++++++++
> > > >    hmp-commands.hx          |  17 +++++
> > > >    4 files changed, 207 insertions(+)
> [...]
> > > > diff --git a/hw/s390x/cpu-topology.c b/hw/s390x/cpu-topology.c
> > > > index ed5fc75381..3a7eb441a3 100644
> > > > --- a/hw/s390x/cpu-topology.c
> > > > +++ b/hw/s390x/cpu-topology.c
> > > > @@ -19,6 +19,12 @@
> [...]
> > > > +
> > > > +void qmp_set_cpu_topology(uint16_t core,
> > > > +                         bool has_socket, uint16_t socket,
> > > > +                         bool has_book, uint16_t book,
> > > > +                         bool has_drawer, uint16_t drawer,
> > > > +                         const char *entitlement_str,
> > > > +                         bool has_dedicated, bool dedicated,
> > > > +                         Error **errp)
> > > > +{
> > > > +    bool has_entitlement = false;
> > > > +    int entitlement;
> > > > +    ERRP_GUARD();
> > > > +
> > > > +    if (!s390_has_topology()) {
> > > > +        error_setg(errp, "This machine doesn't support topology");
> > > > +        return;
> > > > +    }
> > > > +
> > > > +    entitlement = qapi_enum_parse(&CpuS390Entitlement_lookup, entitlement_str,
> > > > +                                  -1, errp);
> > > > +    if (*errp) {
> > > > +        return;
> > > > +    }
> > > > +    has_entitlement = entitlement >= 0;
> > > Doesn't this allow setting horizontal entitlement? Which shouldn't be possible,
> > > only the guest can do it.
> >
> > IMHO it does not, the polarization is set by the guest through the PTF
> > instruction, but entitlement is set by the host.
> Yes, so when the guests requests vertical polarization, all cpus have a
> (vertical) entitlement assigned and will show up as vertical in STSI.
> But now, by using the qmp command, the polarization can be reset to horizontal,
> even though the guest didn't ask for it.


Right, I will change this


Regards,

Pierre