Windows 11 Arm Proc/Memory limits

[CarlinSmith]

Apologies if this has been answered before but didn't find any references in community searches or the unofficial guide.

Is there a hard limit on processor/memory size for Windows 11 arm VMs?  If I try to configure above 4 cores I get a warning that it's more cores than the host has (untrue) and if I configure more than 32GB will get a log error on startup.

Contrast that to the settings for a Linux VM - I don't get the warning on processors until I go one over the physical cores of host which makes total sense. 

Kind regards

[Technogeezer]

There could be some "guard rails" in place for Windows 11 ARM VMs that may not make sense now. With respect to cores, I think you can ignore the warning (but personally I'd never configure the VM for more virtual cores than you have P-cores available. You don't want to over-subscribe cores to the point that macOS decides to run some or all your VM on the E-cores.) 

Memory is another story. There have been reports in the community about warnings/errors when trying to configure large memory configurations for Windows 11 ARM VMs. From what I remember, Broadcom is aware of this but hasn't commented about it.

[CarlinSmith]

Let me add additional clarify - the warning is just incorrect - I have FAR more physical cores than four that triggers the warning with Windows 11.  The warning doesn't occur on the very same machine with a Linux VM.  I can configure the Linux VM to the physical core limit without a warning and as soon as I cross that boundary where virtual > physical I get the warning which seems like logical and correct behavior.

Given this is all done in the hypervisor before the VM is even started what is the logic inside Fusion itself to issue such a warning on Windows.  What I have not researched is whether Windows 11 is imposing that restriction as once the VM is booted Windows clearly identifies the processor type as "Apple Silicon."  This may be the answer but ultimately only VMware can say how the product is intended to function.

[CarlinSmith]

To clarify I have far more physical cores than four.  The Fusion hypervisor shows a warning above four with a Windows VM and it only shows a warning on a Linux VM when the configuration is one more than a physical core.  Same machine same hypervisor but OS is being treated differently as the VMs are not even running at this point.

Maybe Windows 11 has this limitation inherently with Apple Silicon as I noticed in the task manager with the VM running Windows specifically knows it is of type Apple Silicon.

[Technogeezer]

I agree with you that the warning may be flawed.

I have a M1 Mac mini with 4 Performance and 4 Efficiency cores (8 cores total).

Configuring a Windows 11 ARM Pro VM on this machine:

• with 4 cores: no warnings. VM sees 4 cores
• with 6 cores: Warning about VM using too many cores and that guest OS may not be able to use all cores. VM sees 6 cores. The former warning makes sense because I only have 4 P cores in my system. I don't have a system with more P cores to see if the warning exists with more than 4 cores.
• with 8 cores: Same warning as 6 cores. VM sees 8 cores. 

I can't configure the VM on my system above 8 cores.

Which Mac model are you running?

If you power on the VM with the desired number of cores above 4, does the VM power on even though the warnings are present in the GUI? And does the VM actually report that it's seeing the number of cores that you've configured? 

The ultimate source of truth for how many vcpus are configured is the .vmx file. find the entry starting with numvcpus =  and that will tell you how many vCPUs the VM will use. Only 1 socket used for all these cores, unlike for x86_64 VMs. 

As a rule of thumb, though, configure no more than n-2 physical cores to a VM --- the OS, parts of the hypervisor, and other software need some CPU to process the tasks they want to run). You also may wish to limit your VM's cores to the max of the P-core count -   the guest is unaware whether its virtual cores are running on E-cores or P-cores and can't control that like they can on physical hardware (sorry, that's Apple's fault as its their hypervisor frameworks that Fusion uses). . 

On the x64 platform, there used to be distinctions on how many sockets could be supported by Windows Home vs. Pro. On Apple Silicon platforms, there is only 1 socket. I don't know if Windows 11 ARM has any restrictions on core count on Home vs Pro - since all cores will appear as they're on 1 socket.  Perhaps again there's some historical baggage on reporting the "your edition may not support his many sockets/cores" for Windows ARM.

[CarlinSmith]

I have an M1 Max MacBook Pro with 8 performance and 2 efficiency and just received last week an M3 Ultra Mac Studio with 24 Performance Cores and 8 efficiency cores.  On the new Mac Studio, the Linux VM starts complaining at 17 processors which is just 1/2 of the Ultra processor but guessing hypervisor doesn't know how to deal with the UltraFusion connector between the two m3 max processors.  

I am coming from an i9 Intel iMac that had 10 cores but hyper-threaded so presented to OS as 20 cores.  Fusion was very consistent with all VM types on that platform not surprisingly.

The Windows VM despite warning will boot at 8 processors and shows 8 processors in task manager.  If I push memory to 64GB machine will not boot and receive a pipe broken error from VMware.  With 8 cores I can push memory to just under 60GB anything higher generates the pipe error.  Same behavior with a Fedora Linux VM.  8 cores work (no warning) memory must be no higher than 60GB or will get the pipe error.  Lastly, I can even boot the Windows VM with 16 processors as but can't bump memory higher that around this 60GB limit or pipe error.

Really somewhat interesting experiment.

[Technogeezer]

I think we're dealing with two separate issues here.

It sounds like you're running into the problem with memory settings causing the broken pipe hat was reported here in the forums a few months ago.  https://community.broadcom.com/vmware-cloud-foundation/discussion/maximum-allowable-memory-windows-11-virtual-machine  Unfortunately we have not heard anything back from Broadcom about this. 

On the M3 Max studio with memory set to 60GB (the amount that you say you can assign without experiencing the broken pipe), can you assign more than 16 cores to the VM? And if you can, can you VM boot and assign the correct number of vCPUs to the VM?

I tried an experiment as well. I manually edited the vmx file to set the number of cores for the VM to 1 greater than the number of physical cores in my system. The VM failed to power on with a message that the number of virtual cores exceeded the number of physical cores in the system. Dropping the number back to the max number of cores in my system (P+E) still showed the warning in the GUI, but the VM did power on and the guest saw the configured number of cores. 

[CarlinSmith]

The windows VM boots at 16 cores but fails at 17 cores.

[DrBigJim]

I have the M2 Ultra Studio with 24 cores (16 performance and 8 efficiency) and 64 GB of memory and I get the warning any configuration above 4 cores. Configuring the machine for 20 cores generally blue screens the machine. I believe that the in the past, I have been able to configure up to 19 cores and have the system operate. It would be nice to configure the memory of the virtual machines in GBs rather than MBs and the slider definitely preferences smaller memory configurations considering the logarithm scale on the slider. It does seem as VMware only tested on the M1 machines and have minimally updated the software since the initial migration. Hopefully they will provide a great update soon.