VMs utilize only one core

VVF

New Member
Oct 18, 2018
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Hi everyone.

I have the following setup:
Windows 10 PC with Virtualbox with Proxmox running inside. VM with Proxmox was given 6 cores (I have Ryzen 1600 with 6 physical cores). Inside Proxmox I have created an Ubuntu Server 18.04 VM (1 socket, 4 cores, 4 vCPUs, CPU limit: unlimited)

Then I try to simulate a workload on this Ubuntu VM like this: stress-ng -c 0
From inside this VM everything looks fine and if I use htop, I will see expected 100% load on every one of 4 cores. However, if I look at the summary of this VM, I will only see CPU Usage of ~25%.

For experiment's sake, I tried to give this VM only 2 cores and saw ~50% load on the CPU Usage graph. Then only 1 core - 100% load on the CPU Usage graph. So it appears like this VM only uses 1 core no matter what.

One thing to note is that I had to disable KVM Hardware Virtualization in order to make Proxmox work inside Virtualbox (official guide suggested doing so). Could that be the issue?

2nd note:
When I was installing this Ubuntu VM I think I've seen CPU usage jumping up to 70% or something.
 

Carlo Cepelli

New Member
Oct 19, 2018
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I'm having the same problem but with different setup (in case this helps).

- Testing Proxmox on two Kimsufi servers (Atom2800 quad + I7-950 quad+ht)
- Tried both Prox 4.4 and 5.2
- Checked microcodes
- Tried KVM64+Qemu+named matching cpu+host
- Tried using cores and/or sockets
- Tried Win10 and several Debian/Ubuntu versions
- Tried VM and CT
- Tried combinations of microcodes and limits (setting manually instead of microcodes
- Had the impression i passed the 1 core threshold during win installation once (not sure)
- Had the impression it worked properly on a previous versione of 4.4 (the last but one)

- I'm a total newbie in the field, so be patient with tech questions !

Thanks in advance
 

dcsapak

Proxmox Staff Member
Staff member
Feb 1, 2016
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Vienna
One thing to note is that I had to disable KVM Hardware Virtualization in order to make Proxmox work inside Virtualbox (official guide suggested doing so). Could that be the issue?
yes, with tcg, all guest cpus get executed on a single thread -> thus no more than 1 thread per vm in this case
but you really want to use the kvm extensions, otherwise the vm will be very slow (though i cannot say if nesting under virtualbox works)
 

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