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Tue, 6 Dec 2022 21:06:20 +0000 (GMT) Message-ID: <34e774fc372e41f352ccf03761a78eff22728f89.camel@linux.ibm.com> Subject: Re: [PATCH v12 1/7] s390x/cpu topology: Creating CPU topology device From: Janis Schoetterl-Glausch To: Pierre Morel , qemu-s390x@nongnu.org Cc: qemu-devel@nongnu.org, borntraeger@de.ibm.com, pasic@linux.ibm.com, richard.henderson@linaro.org, david@redhat.com, thuth@redhat.com, cohuck@redhat.com, mst@redhat.com, pbonzini@redhat.com, kvm@vger.kernel.org, ehabkost@redhat.com, marcel.apfelbaum@gmail.com, eblake@redhat.com, armbru@redhat.com, seiden@linux.ibm.com, nrb@linux.ibm.com, frankja@linux.ibm.com, berrange@redhat.com, clg@kaod.org Date: Tue, 06 Dec 2022 22:06:20 +0100 In-Reply-To: References: <20221129174206.84882-1-pmorel@linux.ibm.com> <20221129174206.84882-2-pmorel@linux.ibm.com> <92e30cf1f091329b2076195e9c159be16c13f7f9.camel@linux.ibm.com> <3f6f1ab828c9608fabf7ad855098cd6cae1874c4.camel@linux.ibm.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.46.1 (3.46.1-1.fc37) MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 0Hgy3s7gJMllOhgqogKfWympMA5qP41p X-Proofpoint-ORIG-GUID: AnjNGN7cCJJwzroB-MJPmvFU5FeqOB51 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.923,Hydra:6.0.545,FMLib:17.11.122.1 definitions=2022-12-06_11,2022-12-06_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 suspectscore=0 adultscore=0 clxscore=1015 impostorscore=0 mlxscore=0 malwarescore=0 bulkscore=0 lowpriorityscore=0 phishscore=0 mlxlogscore=999 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2210170000 definitions=main-2212060177 Received-SPF: pass client-ip=148.163.158.5; envelope-from=scgl@linux.ibm.com; helo=mx0b-001b2d01.pphosted.com X-Spam_score_int: -19 X-Spam_score: -2.0 X-Spam_bar: -- X-Spam_report: (-2.0 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, 2022-12-06 at 15:35 +0100, Pierre Morel wrote: >=20 > On 12/6/22 14:35, Janis Schoetterl-Glausch wrote: > > On Tue, 2022-12-06 at 11:32 +0100, Pierre Morel wrote: > > >=20 > > > 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. > > > > >=20 > > > > > The device creation is fenced by s390_has_topology(). > > > > >=20 > > > > > Signed-off-by: Pierre Morel > > > > > --- > > > > > 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 > > > >=20 [...] > > > > > =20 > > > > > +static DeviceState *s390_init_topology(MachineState *machine, Er= ror **errp) > > > > > +{ > > > > > + DeviceState *dev; > > > > > + > > > > > + dev =3D qdev_new(TYPE_S390_CPU_TOPOLOGY); > > > > > + > > > > > + object_property_add_child(&machine->parent_obj, > > > > > + TYPE_S390_CPU_TOPOLOGY, OBJECT(dev= )); > > > >=20 > > > > Why set this property, and why on the machine parent? > > >=20 > > > 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. > >=20 > > That I understand. > > >=20 > > > The topology is added to the S390CcwmachineState, it is the parent of > > > the machine. > >=20 > > But why? And is it added to the S390CcwMachineState, or its parent? >=20 > it is added to the S390CcwMachineState. > We receive the MachineState as the "machine" parameter here and it is=20 > added to the "machine->parent_obj" which is the S390CcwMachineState. Oh, I was confused. &machine->parent_obj is just a cast of MachineState* to= Object*. It's the very same object. And what is the reason to add the topology as child property? Just so it shows up in the qtree? Wouldn't it anyway under the sysbus? >=20 >=20 >=20 > > >=20 > > >=20 > > > >=20 > > > > > + object_property_set_int(OBJECT(dev), "num-cores", > > > > > + machine->smp.cores * machine->smp.th= reads, errp); > > > > > + object_property_set_int(OBJECT(dev), "num-sockets", > > > > > + machine->smp.sockets, errp); > > > > > + > > > > > + sysbus_realize_and_unref(SYS_BUS_DEVICE(dev), errp); > > > >=20 > > > > I must admit that I haven't fully grokked qemu's memory management = yet. > > > > Is the topology devices now owned by the sysbus? > > >=20 > > > Yes it is so we see it on the qtree with its properties. > > >=20 > > >=20 > > > > If so, is it fine to have a pointer to it S390CcwMachineState? > > >=20 > > > Why not? > >=20 > > 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. >=20 > Why would it be deallocated ? That's beside the point, if you transfer ownership, you have no control ove= r when the deallocation happens. It's going to be fine in practice, but I don't think you should rely on it. I think you could just do sysbus_realize instead of ..._and_unref, but like I said, I haven't fully understood qemu memory management. (It would also leak in a sense, but since the machine exists forever that s= hould be fine) > as long it is not unrealized it belongs to the sysbus doesn't it? >=20 > Regards, > Pierre >=20