[SOLVED] Proxmox VM Stuck at 3.5 GHz – Unable to Utilize Full CPU Frequency

[rvdmeer]

Hi everyone,

I am running a Proxmox VE setup on an AMD Ryzen 9 3950X with a VM that has 1 core pinned to core 15. Despite my configurations, the CPU inside the VM always stays at 3.5 GHz instead of reaching the 4.76 GHz available on the host.

Setup Details:

• Proxmox Version: 8.2.7
• CPU: AMD Ryzen 9 3950X (16 cores / 32 threads)
• NUMA: Only one node (numactl --hardware confirms this)
• VM Configuration (/etc/pve/qemu-server/2034.conf):
  

  affinity: 15
  agent: enabled=1
  args: -cpu host
  boot: order=scsi0
  cicustom: user=snippets:snippets/2034-su2test01.yaml
  cores: 1
  cpu: host
  ide2: local-zfs:vm-2034-cloudinit,media=cdrom,size=4M
  ipconfig0:
  memory: 2046
  meta: creation-qemu=9.0.2,ctime=1736720464
  name: su2test01
  net0: virtio=BC:24:11:E9:54:F4,bridge=vmbr1,tag=2
  numa: 0
  scsi0: local-zfs:vm-2034-disk-0,size=12G
  scsihw: virtio-scsi-pci
  serial0: socket
  smbios1: uuid=d98c06e2-e468-424e-960f-1ef708cede16
  sockets: 1
  vga: virtio,memory=512
  vmgenid: 9ab6788c-fe7c-4b0b-b94f-0175c14b890b

• Host CPU Frequency (/proc/cpuinfo on Proxmox Host):
  

   cpu MHz: 4762.000

  [*]Guest CPU Frequency (/proc/cpuinfo inside the VM):
  

   cpu MHz: 3499.998

What I’ve Tried So Far:

1. Enabled CPU Passthrough:
   - Set `cpu: host` in VM config
   - Added `args: -cpu host`
2. Checked if CPU scaling is available:
   - /sys/devices/system/cpu/cpu0/cpufreq/ does not exist
   - /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors does not exist
3. Added `amd_pstate=active` to GRUB (/etc/default/grub), updated GRUB, and rebooted.
   - No effect, CPU still stays at 3.5 GHz.
4. Checked dmesg for microcode issues:
   

        dmesg | grep microcode

   - Output:
   

          [    0.003706] Zenbleed: please update your microcode for the most optimal fix
          [    0.703928] microcode: CPU0: patch_level=0x08701021
          [    0.704648] microcode: Microcode Update Driver: v2.2.

Question:

• Why is the VM locked at 3.5 GHz and not utilizing the full 4.76 GHz of the host?
• Is there a way to force Proxmox to pass the full CPU frequency to the guest?
• Should I modify anything in my Proxmox configuration, QEMU settings, or enable additional kernel modules?

Any insights or suggestions would be greatly appreciated!

Thanks in advance!
Ronald

 

[leesteken]

VMs will always show the base clock speed for any virtual thread/code/CPU, even though the actual speed might be higher (or lower) on the actual host thread. This is standard QEMU/KVM behavior.

 

[rvdmeer]

Thank you, that explains alot!