Windows 10 not showing all cores after change to VM cores

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SpeedyVV

Supreme [H]ardness
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Sep 14, 2007
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I'm using UnRAID (KVM), and had a Windows 10 VM with 64 cores.

Now I changed the VM to has 68 Cores, however Task Manager and Device Manager>Processors only still show cores/threads.

Using HWInfo64 it does show that the system does indeed have 68 cores.

Is there something I can do to "refresh" Windows to detect the added cores?

I tried tried Scan for Hardware Changes in Device Manager, but it does not do the trick.
 
Did you reboot the VM? I don't think you can add vCPUs to a running windows instance without a reboot.
 
Yes, rebooted a few times. No luck.

As a matter of fact the VM was powered off when I changed the core count.
 
Boot the VM with a linux distro and see if it shows the correct core count.

Post back so we can further assist ;)
 
I bet its a GUI bug, if msinfo32 shows the correct processor, it should be fine.
 
k1pp3r said:
I bet its a GUI bug, if msinfo32 shows the correct processor, it should be fine.
Click to expand...
Traveling in Australia, but will remote login tonight and report back.


Edit: just logged on.
Processor Intel(R) Xeon(R) CPU E5-2699 v3 @ 2.30GHz, 2295 Mhz, 32 Core(s), 64 Logical Processor(s)
 
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You said you rebooted it, but did you power it off and back on? Typically in the VMware world, you need to do that for the VMX file to update to show properly. A reboot won't do it.
 
This got my curiosity. I've had a read and it definitely should work. Here's an article with examples re: the creation of Windows 8. It clearly shows the desktop OS in a VM displaying 64+ cores in Task Manager etc.

https://blogs.msdn.microsoft.com/b8/2011/10/27/using-task-manager-with-64-logical-processors/

I would follow the advice from QHalo re: the power off, but it sounds to me like you've got a weird OS issue specifically with task manager and device manager. You've confirmed that the correct core count is displayed re: System Info, which to state the obvious is run within the OS, therefore the OS is detecting the correct number.
Weird, but interesting...
 
I'm starting to think that because the OS was installed with 64 threads, this is causing some bug to appear, or something got screwed up.

When I return from my trip, I'm going to reinstall windows and see if this fixes it.
 
SpeedyVV said:
I'm starting to think that because the OS was installed with 64 threads, this is causing some bug to appear, or something got screwed up.

When I return from my trip, I'm going to reinstall windows and see if this fixes it.
Click to expand...

I was going to mention that more than 64 logical processors is when Windows starts to group things into processor groups, so could be on to something there.. It almost reminds of the days when they had separate kernels for single vs multi core, and upgrading to a multi core CPU with the single core kernel would just continue to show 1 CPU. But I can't really find anything that mentions that sort of limitation with 7/8/10.

I haven't used KVM, but could just be a KVM+Windows compatibility thing with more than 64 cores, might need to change the config so it's reporting something like 2x CPUs with 17 cores/34 threads each, instead of 1x CPU with 34 cores/68 threads, if that can be done with KVM.
 
I encountered a similar issue as you, albeit on a much smaller scale and with ESXi. For me, the issue was that by default ESXi presents each vCPU to the guest OS as being in a separate socket, even if they come from the same physical socket, and Windows 10 has pretty strict licensing rules for processor cores/sockets. I played around with the "cores per socket" setting for my VM's config until it was in compliance with my Windows license. All cores are now detected.
 
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