virtualbox.org

Host
Virtualbox 6.1.16
Windows 10 Pro 20H2 19042.685 (x64)
AMD Ryzen 7 2700X Eight-Core Processor
RAM 16,0 GB
Motherboard B450 Tomahawk
MSI Armor RX570
Enabled AMD-V on Motherboard
device manager shows 16 processors

Guest = Host
Windows 10 Pro 20H2 19042.685 (x64)

Problem

In settings >> System >> Processor tab only 2 CPUs are available in the green bar. And the red bar displays up to 4 CPUs.

How to configure Virtualbox to get more processors once the device manager host shows 16 processors?

Is there an interface problem between Virtuabox and the recent version of Window 20H2 with Ryzen 2700 series processors?

The VM's vbox.log will show what Virtualbox thinks about the host PC's CPU count.

Ajuricaba wrote:device manager host shows 16 processors?

Ajuricaba wrote:AMD Ryzen 7 2700X Eight-Core Processor

"16" cores really means 8 cores with AMD-V. From https://www.amd.com/en/products/cpu/amd-ryzen-7-2700x:

# of CPU Cores 8 # of Threads 16

Why only 4 show up in Virtualbox is a puzzle to me. The VM's vbox.log will show what Virtualbox thinks about the host PC's CPU count.

Start the VM from full normal shutdown, not save-state. Run until you see the problem happen, then shut down the VM from within the VM's OS if possible. If not possible, close the Virtualbox window for the VM with the Power Off option set.

Right-click the VM in the main Virtualbox window's VM list, choose Show Log. Save the far left tab's log, zip it, and post the zip file, using the forum's Upload Attachment tab.

The log is the same as the other topic I posted with the title "windows 20H2 slow with 3d acceleration enabled"

scottgus1 wrote:Why only 4 show up in Virtualbox is a puzzle to me.

And only 2 are available. If I put 4, the message "invalid settings detected" appears.

00:00:03.210047 CPUM: Logical host processors: 4 present, 4 max, 4 online, online mask: 000000000000000f
00:00:03.210048 CPUM: Physical host cores: 2
00:00:03.210253 Full Name: "AMD Ryzen 7 2700X Eight-Core Processor "

Virtualbox either isn't reading something right, or isn't being told right by the host OS. Check to see if any chipset drivers or other updates are available. Otherwise, we'll have to wait for some CPU gurus to take a look at this one.

I'm pretty sure VirtualBox gets the core count in the first instance from the host OS, so it's the host OS the OP needs to look at. Was this motherboard upgraded perhaps after Windows was installed?

With your precious help, tips and advice, I managed to solve by installing the processor driver from the link
https://www.amd.com/en/support

Before, I only installed the motherboard drivers and the video card drivers.

And the motherboard and video card drivers are up to date.

thank you

But it did not solve the problem of the other topic "windows 20H2 slow with 3d acceleration enabled". It seems to me that I read on the forum before posting that more people reported the problem of delay with 3D acceleration. Disabling works with good performance, but the goal is to report to give you feedback.

This topic "How to get more processors on windows 20H2 and ryzen 2700x?" can be closed.

Thanks for reporting back.

Regarding the slowness, now that you have a working CPU make sure that Windows hasn't turned on Hyper-v, as that is nearly always the reason for very slow VirtualBox VMs.
See HMR3Init: Attempting fall back to NEM (Hyper-V is active)