On Tue, 2022-12-06 at 11:32 +0100, Pierre Morel wrote:
>
> On 12/6/22 10:31, Janis Schoetterl-Glausch wrote:
> > On Tue, 2022-11-29 at 18:42 +0100, Pierre Morel wrote:
> > > We will need a Topology device to transfer the topology
> > > during migration and to implement machine reset.
> > >
> > > The device creation is fenced by s390_has_topology().
> > >
> > > Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
> > > ---
> > > include/hw/s390x/cpu-topology.h | 44 +++++++++++++++
> > > include/hw/s390x/s390-virtio-ccw.h | 1 +
> > > hw/s390x/cpu-topology.c | 87 ++++++++++++++++++++++++++++++
> > > hw/s390x/s390-virtio-ccw.c | 25 +++++++++
> > > hw/s390x/meson.build | 1 +
> > > 5 files changed, 158 insertions(+)
> > > create mode 100644 include/hw/s390x/cpu-topology.h
> > > create mode 100644 hw/s390x/cpu-topology.c
> > >
> > [...]
> >
> > > diff --git a/include/hw/s390x/s390-virtio-ccw.h b/include/hw/s390x/s390-virtio-ccw.h
> > > index 9bba21a916..47ce0aa6fa 100644
> > > --- a/include/hw/s390x/s390-virtio-ccw.h
> > > +++ b/include/hw/s390x/s390-virtio-ccw.h
> > > @@ -28,6 +28,7 @@ struct S390CcwMachineState {
> > > bool dea_key_wrap;
> > > bool pv;
> > > uint8_t loadparm[8];
> > > + DeviceState *topology;
> >
> > Why is this a DeviceState, not S390Topology?
> > It *has* to be a S390Topology, right? Since you cast it to one in patch 2.
>
> Yes, currently it is the S390Topology.
> The idea of Cedric was to have something more generic for future use.
But it still needs to be a S390Topology otherwise you cannot cast it to one, can you?
>
> >
> > > };
> > >
> > > struct S390CcwMachineClass {
> > > diff --git a/hw/s390x/cpu-topology.c b/hw/s390x/cpu-topology.c
> > > new file mode 100644
> > > index 0000000000..bbf97cd66a
> > > --- /dev/null
> > > +++ b/hw/s390x/cpu-topology.c
> > >
> > [...]
> > >
> > > +static DeviceState *s390_init_topology(MachineState *machine, Error **errp)
> > > +{
> > > + DeviceState *dev;
> > > +
> > > + dev = qdev_new(TYPE_S390_CPU_TOPOLOGY);
> > > +
> > > + object_property_add_child(&machine->parent_obj,
> > > + TYPE_S390_CPU_TOPOLOGY, OBJECT(dev));
> >
> > Why set this property, and why on the machine parent?
>
> For what I understood setting the num_cores and num_sockets as
> properties of the CPU Topology object allows to have them better
> integrated in the QEMU object framework.
That I understand.
>
> The topology is added to the S390CcwmachineState, it is the parent of
> the machine.
But why? And is it added to the S390CcwMachineState, or its parent?
>
>
> >
> > > + object_property_set_int(OBJECT(dev), "num-cores",
> > > + machine->smp.cores * machine->smp.threads, errp);
> > > + object_property_set_int(OBJECT(dev), "num-sockets",
> > > + machine->smp.sockets, errp);
> > > +
> > > + sysbus_realize_and_unref(SYS_BUS_DEVICE(dev), errp);
> >
> > I must admit that I haven't fully grokked qemu's memory management yet.
> > Is the topology devices now owned by the sysbus?
>
> Yes it is so we see it on the qtree with its properties.
>
>
> > If so, is it fine to have a pointer to it S390CcwMachineState?
>
> Why not?
If it's owned by the sysbus and the object is not explicitly referenced
for the pointer, it might be deallocated and then you'd have a dangling pointer.
> It seems logical to me that the sysbus belong to the virtual machine.
> But sometime the way of QEMU are not very transparent for me :)
> so I can be wrong.
>
> Regards,
> Pierre
>
> > > +
> > > + return dev;
> > > +}
> > > +
> > [...]
>
