Forum Discussion

Copper Contributor

Jul 28, 2022

Solved

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 instal...

Hyper-V

Windows Server

SanderNewVM
Aug 09, 2022
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.

SanderNewVM

Copper Contributor

Aug 09, 2022

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.

Intfk

Copper Contributor

Aug 09, 2022

That is interesting, and I'll have a look at my BIOS for sure. For the sake of curiosity, would you mind posting the specs for your two hosts? CPU/motherboard will likely be sufficient. Thanks for posting your findings, and hello again.

Intfk
Copper Contributor
Aug 10, 2022
I don't have the Extreme setting, but changing from Maximum Performance to "just" Performance did indeed fix the issue for me. Thank you, I doubt I'd even attempt that toggle without your post.