Correct configuration for VM Processors

AiroSam

New Member
Jan 13, 2021
13
0
1
27
Hello,

I have Proxmox VE 6.3-3 running on a Dell Server with an Intel® Xeon® Processor E5-2680 v3 (2x 12 core). Hyperthreading is enabled, so a maximum of 48 cores are available.

What is the correct configuration to allow a VM to use all 48 cores? I tried setting Sockets to 2 and Cores to 24, but it actually resulted in worse performance than when Cores was set to 12. Also, what is the impact of enabling NUMA?

Thanks for your time!
 

tburger

Active Member
Oct 13, 2017
778
91
33
38
What is the correct configuration to allow a VM to use all 48 cores
This is an invalid configuration.
Because you don't have 48 cores. You have 48 threads.
You have 24 coresand even those should not be assigned to one VM.
Size to your workload. Not to your hardware!
 

AiroSam

New Member
Jan 13, 2021
13
0
1
27
In that case, let's say I wanted to have 44 "threads" assigned to one VM. What is the proper configuration for that?
 

tburger

Active Member
Oct 13, 2017
778
91
33
38
You have 24 cores and even those should not be assigned to one VM.
If you want to hear it or not. Thats the way it is. Recommended practice: stay within one NUMA-node (12 vCPUs in your case).
You are not doing the system any good with what you want to do.
Looks pretty / impressive perhaps, but doesnt perform as you expect.
 

AiroSam

New Member
Jan 13, 2021
13
0
1
27
I don't think the main point is being addressed here. I'm trying to get answers on how to actually configure the CPU settings. The way it's configured now only allows 24 cores to show up in the VM, which isn't enough for what the VM is doing.
 

tburger

Active Member
Oct 13, 2017
778
91
33
38
which isn't enough for what the VM is doing.
Then get yourself other gear.
What you try to achieve does not make sense at all from a technical persepcetive.
Reason: If that is not enough. More threads wont help. You only have 24 cores. Physically.

Threads wont help. You create contention on the host. Which will slow things further down.

If you really want to go with 48 threads: go physical. Install your OS on the hardware itself. Skip virtualization.
 

AiroSam

New Member
Jan 13, 2021
13
0
1
27
Then get yourself other gear.
What you try to achieve does not make sense at all from a technical persepcetive.
Reason: If that is not enough. More threads wont help. You only have 24 cores. Physically.

Threads wont help. You create contention on the host. Which will slow things further down.

If you really want to go with 48 threads: go physical. Install your OS on the hardware itself. Skip virtualization.

It sounds like you're suggesting that hyperthreading has no benefit for VMs? Why is that?
 

tburger

Active Member
Oct 13, 2017
778
91
33
38
it has a potential benefit to the host.
but the host needs to schedule all these cores.
And assigning all the cores puts pressure on the host. It can t breathe.
Hence it will pause the VM from time to time to get its own stuff done.
it is a misconception (a huge one) that VCPUs come for free. Surprise! They dont.
Hence my recommendation.
I even go that far that likely I would say the VM you are trying to build will perform BETTER with LESS cores.
Why? Because it actually can get those scheduled fairly easy.
 

AiroSam

New Member
Jan 13, 2021
13
0
1
27
it has a potential benefit to the host.
but the host needs to schedule all these cores.
And assigning all the cores puts pressure on the host. It can t breathe.
Hence it will pause the VM from time to time to get its own stuff done.
it is a misconception (a huge one) that VCPUs come for free. Surprise! They dont.
Hence my recommendation.
I even go that far that likely I would say the VM you are trying to build will perform BETTER with LESS cores.
Why? Because it actually can get those scheduled fairly easy.

I appreciate the info!
 

About

The Proxmox community has been around for many years and offers help and support for Proxmox VE, Proxmox Backup Server, and Proxmox Mail Gateway.
We think our community is one of the best thanks to people like you!

Get your subscription!

The Proxmox team works very hard to make sure you are running the best software and getting stable updates and security enhancements, as well as quick enterprise support. Tens of thousands of happy customers have a Proxmox subscription. Get your own in 60 seconds.

Buy now!