On 11/16/22 17:51, Christian Borntraeger wrote:
Am 02.09.22 um 09:55 schrieb Pierre Morel:
Hi,
The implementation of the CPU Topology in QEMU has been drastically
modified since the last patch series and the number of LOCs has been
greatly reduced.
Unnecessary objects have been removed, only a single S390Topology object
is created to support migration and reset.
Also a documentation has been added to the series.
To use these patches, you will need Linux V6-rc1 or newer.
Mainline patches needed are:
f5ecfee94493 2022-07-20 KVM: s390: resetting the Topology-Change-Report
24fe0195bc19 2022-07-20 KVM: s390: guest support for topology function
0130337ec45b 2022-07-20 KVM: s390: Cleanup ipte lock access and SIIF
fac..
Currently this code is for KVM only, I have no idea if it is interesting
to provide a TCG patch. If ever it will be done in another series.
To have a better understanding of the S390x CPU Topology and its
implementation in QEMU you can have a look at the documentation in the
last patch.
New in this series
==================
s390x/cpus: Make absence of multithreading clear
This patch makes clear that CPU-multithreading is not supported in
the guest.
s390x/cpu topology: core_id sets s390x CPU topology
This patch uses the core_id to build the container topology
and the placement of the CPU inside the container.
s390x/cpu topology: reporting the CPU topology to the guest
This patch is based on the fact that the CPU type for guests
is always IFL, CPUs are always dedicated and the polarity is
always horizontal.
This may change in the future.
hw/core: introducing drawer and books for s390x
s390x/cpu: reporting drawers and books topology to the guest
These two patches extend the topology handling to add two
new containers levels above sockets: books and drawers.
The subject of the last patches is clear enough (I hope).
Regards,
Pierre
Pierre Morel (10):
s390x/cpus: Make absence of multithreading clear
s390x/cpu topology: core_id sets s390x CPU topology
s390x/cpu topology: reporting the CPU topology to the guest
hw/core: introducing drawer and books for s390x
s390x/cpu: reporting drawers and books topology to the guest
s390x/cpu_topology: resetting the Topology-Change-Report
s390x/cpu_topology: CPU topology migration
target/s390x: interception of PTF instruction
s390x/cpu_topology: activating CPU topology
Do we really need a machine property? As far as I can see, old QEMU
cannot activate the ctop facility with old and new kernel unless it
enables CAP_S390_CPU_TOPOLOGY. I do get
oldqemu .... -cpu z14,ctop=on
qemu-system-s390x: Some features requested in the CPU model are not
available in the configuration: ctop
With the newer QEMU we can. So maybe we can simply have a topology (and
then a cpu model feature) in new QEMUs and non in old. the cpu model
would then also fence migration from enabled to disabled.
OK, I can check this.
In this case migration with topology will be if I understand correctly:
NEW_QEMU/old_machine <-> NEW_QEMU/old_machine OK
While
OLD_QEMU/old_machine <-> NEW_QEMU/old_machine KO
NEW_QEMU/old_machine <-> OLD_QEMU/old_machine KO
Is this something we can accept?
regards,
Pierre
--
Pierre Morel
IBM Lab Boeblingen
