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Abysmal Performance in Fusion 12 after upgrade to macOS Big Sur

After upgrading to macOS Big Sur, performance on my VMs went from great to utterly abysmal. Remedial tasks like opening the Start menu, opening Notepad etc. can now take up to half a minute. Windows are drawn on the screen line-by-line with half second intervals.

The host computer is a 2018 Mac mini with ample memory, disk and CPU. The issue was not present under Fusion 12.0.0 before upgrading to macOS Big Sur. Toggling "Disable Side Channel Mitigations" has no effect.

The attached screenshot shows the vmx processes of three VMs after the VMs have been idling overnight, with no applications open. The VMs (running Windows 10) are pegging the CPU while doing nothing.

Screenshot 2020-11-17 at 08.07.53.png

 

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Champion
Champion

Nope, not responding to you, sorry.  Regressions like this are frustrating - hopefully Apple will fix it in their hypervisor framework in 11.1.

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hopefully Apple will fix it in their hypervisor framework in 11.1

I remain amazed that they went for that framework in the first place, given their overall long term trajectory in terms of x86...

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Good news – Fusion 12.1.0 just arrived, and it does fix the performance problem for me, i.e. with "side channel mitigations" re-enabled, it seems as fast as it was before the Catalina to Big Sur update earlier this week. Yay, thanks VMware!

 

https://docs.vmware.com/en/VMware-Fusion/12.1.0/rn/VMware-Fusion-1210-Release-Notes.html

  • Performance improvements, bug fixes and security updates
  • Nested virtualization is not supported without VMCS shadowing
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@nobody456  Could you tell us a bit about your virtual machine and Mac hardware specs?

Are you doing VBS (Virtualization Based Security) with a TPM or just a VM within that VM or something?  I'd rather not go through the pain of updating to Big Sur again and then having to back off to Catalina.

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Could you tell us a bit about your virtual machine and Mac hardware specs?

sure – spring 2020 MBA (4C/8T Icelake, 16G, 2T), BS 11.0.1, Fusion 12.1.0 + W2K SP4 VM (installed as 2C, usually run as 1C, VM HW v18)

Are you doing VBS (Virtualization Based Security) with a TPM or just a VM within that VM or something?

no TPM, no nesting – just a simple VM
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yeah, that's crazy

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Ok thanks, sounds like this isn't going to affect the problem I have.

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As a general update: The issue has not been resolved with the 12.1.0 (17195230) update. The issue remains present when "Core isolation" is enabled in Windows while "Enable hypervisor applications in this virtual machine" is turned on.