** Description changed:
[ Impact ]
- QEMU users on Ubuntu Jammy who try to spawn a VM with more than 288
- vCPUs will not be able to do so, because the machine types available
+ QEMU users on Ubuntu Jammy/Mantic who try to spawn a VM with more than
+ 288 vCPUs will not be able to do so, because the machine types available
don't support such scenario. The following error will happen:
qemu-system-x86_64: Invalid SMP CPUs 300. The max CPUs supported by
machine 'pc-q35-jammy' is 288
[ Test Plan ]
Ideally, the test should be performed in a machine with more than 288
physical CPUs available. However, due to the difficulty in finding such
systems, it is possible to emulate the usage of more than 288 vCPUs.
- On a Jammy machine, you can do:
+ On a Jammy/Mantic machine, making sure to adjust the machine type
+ accordingly, you can do:
$ sudo qemu-system-x86_64 -M pc-q35-jammy,accel=kvm,kernel-irqchip=split
-device intel-iommu,intremap=on -smp cpus=300,maxcpus=300 -enable-kvm
-net none -m 4096M -nographic -kernel /boot/vmlinuz -initrd
/boot/initrd.img -chardev stdio,mux=on,id=char0 -mon
chardev=char0,mode=readline -serial chardev:char0 -append
"console=ttyS0"
You will notice that the command will fail, as expected.
- The proposed fix is to create a new machine type on Jammy, in order to
- minimize the possibility of regressions in deployments using the
- existing machine types. This new type is named pc-{q35,i440fx}-jammy-
- maxcpus. When doing the test, make sure to provide this new machine
- type (as part of the "-M" argument).
+ The proposed fix is to create a new machine type on Jammy/Mantic, in
+ order to minimize the possibility of regressions in deployments using
+ the existing machine types. This new type is named
+ pc-{q35,i440fx}-{jammy,mantic}-maxcpus. When doing the test, make sure
+ to provide this new machine type (as part of the "-M" argument).
[ Where problems could occur ]
As explained above, a new machine type was created in order to minimize
the possibility of regressions. As such, the existing
- "pc-{q35,i440fx}-jammy" machine types should continue to work as before,
- without any change.
+ "pc-{q35,i440fx}-{jammy,mantic}" machine types should continue to work
+ as before, without any change.
[ Original Description ]
During testing of an AMD Genoa CPU, it was discovered that qemu-system-
amd64 doesn't support enough cpus.
The specific error the tester received was:
qemu-system-x86_64: Invalid SMP CPUs 384. The max supported by machine
'pc-q35-7.1' is 288
Looking at the sournce that seems to be an easy fix at first glance:
https://github.com/qemu/qemu/blob/master/hw/i386/pc_q35.c
372 machine_class_allow_dynamic_sysbus_dev(m, TYPE_VMBUS_BRIDGE);
373 m->max_cpus = 288;
--
You received this bug notification because you are a member of Ubuntu
Bugs, which is subscribed to Ubuntu.
https://bugs.launchpad.net/bugs/2012763
Title:
qemu-system-amd64 max cpus is too low for latest processors
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/lxd/+bug/2012763/+subscriptions
--
ubuntu-bugs mailing list
ubuntu-bugs@lists.ubuntu.com
https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
