Comment 61 for bug 2012763

So after we talked on MM, I think maybe you and Simon have been testing
this instead, so for now is do I need to do this?

Thanks
Jeff

On Tue, Mar 19, 2024 at 3:10 PM Sergio Durigan Junior <
<email address hidden>> wrote:

> Hi Jeff,
>
> Thanks for the offer. Actually there is!
>
> - If you could test Noble and double/triple check that we don't need to
> do anything else there in order to support maxcpus, that'd be great.
> Just use the "ubuntu" machine type and check if QEMU starts correct with
> more than 288 vCPUs.
>
> - Once the Jammy/Mantic SRUs are accepted, we will need to perform a
> verification for both uploads. I can do it my side, but it would be
> very helpful if you could also verify the uploads on your side.
>
> Thanks.
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/2012763
>
> Title:
> qemu-system-amd64 max cpus is too low for latest processors
>
> Status in lxd package in Ubuntu:
> New
> Status in qemu package in Ubuntu:
> Confirmed
> Status in lxd source package in Jammy:
> New
> Status in qemu source package in Jammy:
> New
> Status in lxd source package in Lunar:
> Invalid
> Status in qemu source package in Lunar:
> Invalid
> Status in lxd source package in Mantic:
> New
> Status in qemu source package in Mantic:
> Confirmed
> Status in lxd source package in Noble:
> New
> Status in qemu source package in Noble:
> Confirmed
>
> Bug description:
> [ Impact ]
>
> 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/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/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,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;
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/ubuntu/+source/lxd/+bug/2012763/+subscriptions
>
> Launchpad-Notification-Type: bug
> Launchpad-Bug: distribution=ubuntu; sourcepackage=lxd; component=universe;
> status=New; importance=Undecided; assignee=None;
> Launchpad-Bug: distribution=ubuntu; sourcepackage=qemu; component=main;
> status=Confirmed; importance=Critical; assignee=
> <email address hidden>;
> Launchpad-Bug: distribution=ubuntu; distroseries=jammy; sourcepackage=lxd;
> component=None; status=New; importance=Undecided; assignee=None;
> Launchpad-Bug: distribution=ubuntu; distroseries=jammy;
> sourcepackage=qemu; component=main; status=New; importance=Undecided;
> <email address hidden>;
> Launchpad-Bug: distribution=ubuntu; distroseries=lunar; sourcepackage=lxd;
> component=None; status=Invalid; importance=Undecided; assignee=None;
> Launchpad-Bug: distribution=ubuntu; distroseries=lunar;
> sourcepackage=qemu; component=main; status=Invalid; importance=Undecided;
> <email address hidden>;
> Launchpad-Bug: distribution=ubuntu; distroseries=mantic;
> sourcepackage=lxd; component=None; status=New; importance=Undecided;
> assignee=None;
> Launchpad-Bug: distribution=ubuntu; distroseries=mantic;
> sourcepackage=qemu; component=main; status=Confirmed; importance=Critical;
> <email address hidden>;
> Launchpad-Bug: distribution=ubuntu; distroseries=noble; sourcepackage=lxd;
> component=None; status=New; importance=Undecided; assignee=None;
> Launchpad-Bug: distribution=ubuntu; distroseries=noble;
> sourcepackage=qemu; component=main; status=Confirmed; importance=Critical;
> <email address hidden>;
> Launchpad-Bug-Information-Type: Public
> Launchpad-Bug-Private: no
> Launchpad-Bug-Security-Vulnerability: no
> Launchpad-Bug-Commenters: anilchabba bladernr goujm1 junggyumkim mcoskey
> mjt+launchpad-tls paelzer racb rodsmith sergiodj
> Launchpad-Bug-Reporter: Jeff Lane  (bladernr)
> Launchpad-Bug-Modifier: Sergio Durigan Junior (sergiodj)
> Launchpad-Message-Rationale: Subscriber
> Launchpad-Message-For: bladernr
>
>

--
Jeff Lane
Engineering Manager
IHV/OEM Alliances and Server Certification

"Entropy isn't what it used to be."