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scoubix
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Poor overvall performance of Fusion 12 with old Windows as guests with Big Sur beta host...even with side channel mitigations disabled

Hi,

Had Fusion upgraded from 11.5.x (whatever the latest was) to 12.0 on my 10.5.6 Catalina MBP 16'' earlier this week, did the same on my Mac mini late 2012 host as well, performance was identical to Fusion 11.5, and then upgraded my Catalina MBP to the latest Big Fur public beta, which went all.

I then noticed a significant drop in overall performance of some of my guests VMs. I turned off the side-channel mitigation feature in my VMs settings, as suggested, but no improvement noticeable.

Symptoms are :

- much slower graphics (windows being drawn on screen are noticeable)

- much slower "CPU feel" performance, including boot-up time, time to get to desktop once logged in, launching apps...

This happens with three of my guests, namely Win2K, Win98SE and WinXP. Strangely enough, my Win7 VM runs apparently as quickly as before, possibly even faster, and is now my guest OS that runs the quickest out of all 4, which certainly wasn't the case before.

The exact same VMs (as they've been copied between my hosts) still run perfectly fine with Fusion 12 on my Catalina Mac mini host, thus using the older kext virtualization engine, so I'm guessing the issue is related to the API virtualization engine of Big Sur. For sure Big Sur is still in beta, but was wondering if this is to be expected or what solutions/troubleshooting you'd suggest?

Already tried :

- resinstalling Tools in said guests

- reinstalling Fusion 12 from scratch in Big Sur

- adjusting number of CPU cores/RAM in Win2k and WinXP guests

Thanks

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covelli
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Older Windows guests such as Win98, Win2K and WinXP were written in a time before virtualization was widespread and cause a staggering number of vmexits by frequently accessing the local APICs TPR (task priority register).  To avoid these exits Intel introduced a feature called flex priority/TPR shadowing.  Unfortunately there was a delay in getting this to work on BigSur but it should be enabled in a future release. 

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covelli
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Older Windows guests such as Win98, Win2K and WinXP were written in a time before virtualization was widespread and cause a staggering number of vmexits by frequently accessing the local APICs TPR (task priority register).  To avoid these exits Intel introduced a feature called flex priority/TPR shadowing.  Unfortunately there was a delay in getting this to work on BigSur but it should be enabled in a future release. 

scoubix
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Thanks for the feedback. Here's to hoping this gets fixed in the first delivered update to Fusion 12. It's a major setback for me and one I wouldn't have expected after years of using Fusion.

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herrugatto
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Now, I know why the things that aren't supposed to lag like old games on a Windows XP guest are lagging. Thank you.

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WTell
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I'm experiencing the exact same issue that you are describing (very poor performance, windows being drawn line by line, Start menu takes about 10 seconds to appear) after upgrading to Big Sur. Did you find any resolution yet?

Edit: Are you by any chance running any particular antivirus on your VMs?

WTell
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Try disabling "Enable hypervisor applications in this virtual machine" under Processors & Memory in the VM settings. That fixed the issue for me, however, I rely on this feature so this is not a fix that I can use.

ddjfm
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The problem is still there in macOS Big Sur 11.2.3 and VMWare Fusion 12.1.1. After upgrading to Big Sur from OS X El Capitan (i think) my Windows 10 host runs extremely slow, my Windows 7 host runs at "normal" speed. Any new hints out there?

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ColoradoMarmot
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If you have to have nested hypervisors enabled, there's not much you can do.

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ddjfm
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No, I have no need to have nested hypervisors enabled and it is not enabled. Can I do anything?

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ColoradoMarmot
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What's the host and guest CPU and RAM configuration?

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