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Intfk
Copper Contributor
Jul 28, 2022

Installing Hyper-V on Windows Server 2022 reduces host system CPU to 1 core 1 thread

Bit of an odd situation, I've installed Windows Server 2022 (desktop experience) on a server, installed MegaStorage MSM and the relevant drivers from Supermicro and any Windows updates. When I install the role HyperV (just the Windows feature Hyper V, not any VMs), my host goes from 8c16t to 1c1t. I thought it might be a visual bug, but it runs like a snail stuck in syrup, so it seems like it's running on 1c. The L1 and L2 caches reported by Task Manager are also altered, but the reported caches are 1/8s of total cache, so it fits the core reduction.

 

I'm not experienced with Server 2022, and I've only really set up HyperV and VMs on Windows 7/10/11 as well as VirtualBox previously, so it's entirely possible this is amateur hour and I've forgotten to set/install something basic and obvious.

As for the usual suspects, I've double checked BIOS settings (originally set by the hardware supplier) and everything VT-related looks enabled. The msconfig -> Boot -> Advanced -> "Number Of Processors" check box is unchecked.

 

My supplier suggested it might be a Server 2022 software issue, so I installed Windows Server 2019 (evaluation edition, no license) and it just works. HyperV goes in, CPU remains 8c16t. I upgraded that install with HyperV enabled from Server 2019 (eval) to Server 2022 (licensed) and the upgrade reduces my host CPU to 1c1t.

 

The system in question:

Motherboard: Supermicro X11SPL-F running 3.6 BIOS
CPU: Intel Xeon Silver 4208SP 8c16t
RAM: 16GB DDR4 3200MHz ECC Registered 2Rx8 Samsung x4
Controller: Avago/Broadcom/LSI/whatever the flavour of the month SAS9341-8i
Storage: 2x Samsung PM883 SSD 960GB running RAID1

Here are screenshots of the feature list, Task Manager and Device Manager before and after: https://ibb.co/v1mP8Zn https://ibb.co/6Z6xj7C

 

 

Edit: Corrected feature to role.

I went through the logs and there's an error being thrown just after HyperV is installed.

Event 97: "Hypervisor processor startup failed (APIC ID 0x0) due to CPUID feature validation error. Further processors in the system were not started. Leaf 0x1, register 0x2 feature mismatch: BSP has features 0x77FEFBF7; AP has features 0x0"

I see other people have reported this error for previous Windows Server versions.

My exact CPU specs are:

Processor Name: Intel(R) Xeon(R) Silver 4208 CPU @ 2.10GHz

Type : 0 Family : 6

Model : 55

Stepping : 7

Revision: 500320A

 

  • Got it! My colleague searched and searched for it. And found a workaround!
    Ok, the workaround is nasty and shows a problem in how HyperV 2022 in somewhere in the latest Windows Updates communicates with the BIOS and CPU.

    In the BIOS, go to Advanced -> CPU Configuration -> Advanced Power Management Configuration -> "ENERGY_PERF_BIAS_CFG mode". Edit this option.


    You will find six options;
    * Extreme Performance (does not work)
    * Maximum Performance (does not work)
    * Performance (works)
    * Balanced Performance (works)
    * Balanced Power (works)
    * Power (works)

     

    See following screenshot as example:

     

    Select one of the working templates and you will get the CPU cores back.

     

    But why?! It looks like there is something wrong with the exposure of the CPU C-states. In this particular situation is looks like it have to do something with CPU masks and with HyperV not accepting/recognizing them:
    "Extended Auto-HALT State C1E"

     

    Sander.

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