KVM and hyperthreading

[GwennG]

Hi,

We've added a new node in our proxmox cluster with 2 Quad-core Xeon E5520.
It seems these CPUs support HT as the system reports 16 processors.

We created a KVM guest with ubuntu 9.04 jaunty. When setting smp parameter to more than 8 (number of physical cores of the host), the guest fails to boot with a kernel panic (acpi_processor_start).

Is this a normal behaviour ? Can KVM use hyperthreading pseudo-cores ?

Regards.

PS: sorry for posting into wrong forum
Is it possible to move this thread to the PVE installation forum?

 

[tom]

Hi,

We've added a new node in our proxmox cluster with 2 Quad-core Xeon E5520.
It seems these CPUs support HT as the system reports 16 processors.

We created a KVM guest with ubuntu 9.04 jaunty. When setting smp parameter to more than 8 (number of physical cores of the host), the guest fails to boot with a kernel panic (acpi_processor_start).

Is this a normal behaviour ? Can KVM use hyperthreading pseudo-cores ?

Regards.

PS: sorry for posting into wrong forum
Is it possible to move this thread to the PVE installation forum?

you can assign currently up to 16 vcpu´s to a VM (also starts if you just have a single quad-core CPU without HT on the host - worked here without any problems so its in dependable what you go on the host).

but assigning more vcpu´s than physicals makes no sense under normal circumstances. But I have no 5520 system here so I cannot verify.

 

[GwennG]

you can assign currently up to 16 vcpu´s to a VM (also starts if you just have a single quad-core CPU without HT on the host - worked here without any problems so its in dependable what you go on the host).

Thanks for your reply. I'll try with another guest kernel.

 

[GwennG]

Thanks for your reply. I'll try with another guest kernel.

For information, I tried with the following guest kernels:
- 2.6.26-2 from debian-testing : kernel boots but only 8 vcpus detected out of 12
- 2.6.30-1 from debian-unstable : kernel boots and all 12 vcpus detected in the guest

# pveversion -v
pve-manager: 1.3-1 (pve-manager/1.3/4023)
qemu-server: 1.0-14
pve-kernel: 2.6.24-8
pve-kvm: 86-1
pve-firmware: 1
vncterm: 0.9-2
vzctl: 3.0.23-1pve3
vzdump: 1.1-2
vzprocps: 2.0.11-1dso2
vzquota: 3.0.11-1