Re: [PATCH v12 1/7] s390x/cpu topology: Creating CPU topology device

[Pierre Morel <pmorel@linux.ibm.com>]

On 12/1/22 10:08, Thomas Huth wrote:
> On 29/11/2022 18.42, 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@linux.ibm.com>
>> ---
> ...
>> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
>> index 2e64ffab45..973bbdd36e 100644
>> --- a/hw/s390x/s390-virtio-ccw.c
>> +++ b/hw/s390x/s390-virtio-ccw.c
>> @@ -44,6 +44,7 @@
>>   #include "hw/s390x/pv.h"
>>   #include "migration/blocker.h"
>>   #include "qapi/visitor.h"
>> +#include "hw/s390x/cpu-topology.h"
>>   static Error *pv_mig_blocker;
>> @@ -102,6 +103,24 @@ static void s390_init_cpus(MachineState *machine)
>>       }
>>   }
>> +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));
>> +    object_property_set_int(OBJECT(dev), "num-cores",
>> +                            machine->smp.cores * 
>> machine->smp.threads, errp);
> 
> I wonder what will happen if we ever support multithreading on s390x 
> later? ... won't this cause some oddities when migrating older machines 
> types with smp.threads > 1 later? Maybe we should prohibit to enable the 
> CPU topology instead if a user tried to use threads > 1 with an older 
> machine type?

Yes, right, I forgot to change this back.
Anyway it has no sens for new machine which prohibit smp.threads > 1 
neither.

I change this by returning an error in case we have smp.threads > 1

Thanks.

Pierre

> 
>   Thomas
> 
> 
>> +    object_property_set_int(OBJECT(dev), "num-sockets",
>> +                            machine->smp.sockets, errp);
>> +
>> +    sysbus_realize_and_unref(SYS_BUS_DEVICE(dev), errp);
>> +
>> +    return dev;
>> +}
> 

-- 
Pierre Morel
IBM Lab Boeblingen