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dcobb013
Enthusiast
Enthusiast

Win 10 BSOD - BAD SYSTEM CONFIG INFO when booting < 5 CPUs

  • Happy Win 10 VM, running on MBP i9 w/6 physical cores + hyper threading.
  • VM was created with 6 CPUs.
  • Any attempt to reduce the number of CPUs to 4 or less causes BSOD at Windows boot.
    • winload.efi missing or corrupt.
    • attempt to repair via ISO boot fails.
  • Raising CPUs back to 5 or more successfully boots.

  • Catalina 10.15.4
  • Fusion Professional Version 11.5.3 (15870345)
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ColoradoMarmot
Champion
Champion

That's very odd....must be something in windows that fails to downgrade properly when the hardware changes.

FWIW, the rule of thumb for good performance is that no individual guest should have more than N-1 virtual cores, where N is the number of physical cores in the machine.  For yours, that'd be 5.  Using 6 can starve the host.  I've found on my i9 that going over 4 can cause host stuttering too.

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dcobb013
Enthusiast
Enthusiast

Thanks for the response and performance advice. I wish that was my biggest problem today 8^)

On my i9, Fusion sees 12 cores (6 phys and 6 HT) - If I select 6, are you saying that Fusion will use all 6 physical cores? I didn't know that!

I'm perplexed about this CPU count behavior too - it seems to be happening pretty early in the boot cycle - is there some HW dependency that's not being reflected properly in firmware handling?

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ColoradoMarmot
Champion
Champion

Yeah, hyperthreading doesn't count - it's all about physical cores.

This is the only thing I can think of:

Stuck on BSOD Bad system config info after changing number of cores - Microsoft Community

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