Abysmal Performance in Fusion 12 after upgrade to macOS Big Sur

[WTell]

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.

[Kyle_Z]

Hi - where did the n-1 cores requirement come from - this has not been a requirement with past versions?  I can confirm however that a Windows 10 guest blue screens when I try to set the number of cores to n.

[ColoradoMarmot]

It's been there since Fusion 1.0.  You can technically exceed it, but you risk starving the host for cycles, which can cause the whole machine to lockup.  N-1 for any individual VM, and I've found that on an 8-core machine, no more than 6 cores across all VM's gives the best performance.  Also leaving a minimum of 2GB RAM (4 is ideal) for the host as well.

Windows 10 shouldn't bluescreen, unless you're exceeding the number of cores that it can actually handle (I don't recall what the OS cap is).  

[Kyle_Z]

Thanks for the quick response - FWIW I do observe that turning off nested virtualization returns VM to usable status

The irony here is most folks using Fusion are looking for nested virtualization which worked fine in Fusion up to v11

I hope VMware / Apple are able to restore this functionality

[ColoradoMarmot]

Yeah, the switch to the Apple hypervisor has made that feature (especially on older CPU's) a real problem.

[Kyle_Z]

For frame of reference what would you consider and older CPU

[ColoradoMarmot]

According to Apple, the one in the last 16" MBP would fall into that category 🙂

There's specific feature that's needed to enable it to function properly.  VMWare found a workaround that would allow it to run on other CPU's, but as you've seen, performance is terrible.  From what I understand, it's on Apple to fix - but given their Mx chip focus, well, optimizing for Intel machines doesn't seem to be a high priority.

[Kyle_Z]

Sounds like the best bet for an intel based Mac is to be on Catalina and probably Fusion 11 or 12 (I understand on Catalina 12 runs the same way 11 would have - kext)

[ColoradoMarmot]

If you need nested hypervisor, yup, that'd be the way to go for how.

[nobody456]

might as well bite the bullet, and start migrating off of MacOS altogether – with Apple's Arm trajectory, x86 VMs got no future on 

[mysticole928]

Edit: I take it all back.  I could run WSL2 to update my Linux OS but, running "brew update" caused the whole VM" to stop working.  Rats.

I just updated to MacOS 11.2.

Things are marginally better.  (Barely.)  I can (at the very least) use WSL2 to update my Linux VMs.  It still runs slow but it is fast enough to actually do the updates.

I don't think the speed will be fast enough to be usable but it's something.

[mlippold1]

That is my direction as well.   As soon as my iMac is a bit long in the tooth (staying on Catalina) I guess I'm back to a PC and Hyper-V.

[dballve]

Ping! Anything new about this one? Does VMWare have any light at the end of the tunnel to share with the user community?

I'm using heavy software inside VM, with nested VMs and WSL2, Fusion 12 + BigSur is useless to run it. I've converted it VM to Parallels and it runs a lot better there, so I can discard my Mac/OSX or my Windows 10 image as source of the slowness.

[mysticole928]

There was an update to Fusion this week.

I was hopeful but there was no change.

How can this be ignored for so long?

At this point, I'd be happy with an acknowledgment that there is an issue and a hint that it's being addressed.

[mlippold1]

Still <crickets>.    Would it kill someone from vmware to just say "we are working on it" or... "Apple is working on it"?

[SimonPlusNumber]

Any update on this?  I had the same issue, and just gave up on upgrading to Big Sur. Wondering if it's been resolved yet, but not willing to throw a day away making backups, installing the new OS, and then reverting back to Catalina if it's still broken.

[dieter_stockhau]

For me https://communities.vmware.com/t5/VMware-Fusion-Discussions/VMware-Fusion-12-1-0-Big-Sur-Host-Window... was the solution.

[dballve]

Looks better here too, thanks!

[mlippold1]

Do either of you run Windows 10 with a TPM and "Enable VBS (Virtualization Based Security)" enabled?   I suspect this isn't the fix for that performance problem but figured I'd ask.

[mysticole928]

TPM is off.

I've double-checked the core isolation settings.  It's off too. 

Later, when I have some time, I'm going to play with adding some of the Windows Hyper-V features to Windows 10.  

[dieter_stockhau]

Right. Neither TPM nor VBS is enabled.