Adding more CPU's make Win10 guest slower

[vzaporozhsky]

Hello! Sorry for my bad english.

I have a problem when adding two or more vCPU's to the Win10 guest by Win10 host with Ryzen 1400 (4 core 3.20 GHz 16Gb RAM).
When i add more vCPU's, the guest seems to slow down. It takes hours to boot it up. But on 1 vCPU it pretty fast to launch.
I need to test program on 4 vCPU's on that machine. How can i make it?

I saw same issue here: viewtopic.php?f=6&t=77326
But the topic ended in nothing.

[vzaporozhsky]

Here's the log in attachement's.

[mpack]

When i add more vCPU's, the guest seems to slow down.

It's expected that adding unnecessary cores will make the guest slower, especially when you don't leave any cores for the host to use. You have a 4 core host. Assigning 4 cores to the VM leaves 0 cores for the host. But it shouldn't take hours to boot up.

Give the VM 2 cores. Not more, not less.

In the VM settings, System tab, set the "Paravirtualization Interface" to "Hyper-v". This has nothing to do with the next item btw.

Disable Hyper-v on your host (yes it is): see the last post in FAQ: I have a 64bit host, but can't install 64bit guests.

Install the Extension Pack, then I would enable xHCI (USB3).

Disable Transparency Effects in the guest, then enable 3D acceleration in the VM settings. Then increase graphics RAM to 256MB.