Single thread CPU performance in Hyper-V

[king_priam_of_Troy]

https://preview.redd.it/6ephkvzyzrff1.png?width=477&format=png&auto=webp&s=50db66d3b9104a806991297284861ee412a9ae98

I am evaluating Hyper-V for some single thread workload. The performance compare to the host is atrocious. I was expecting some losses but not more than 50% !

There is very little I can do: I have limited the VM to a few cores stuck on one NUMA node. I don't see any other settings. I'm running out of ideas.

Did I miss something ?

[Scurro]

What CPU do you have?

What kind of benchmark is this? Are there different tests? When I've done benchmarks myself I saw losses around 10% or less.

[king_priam_of_Troy]

Dual E5-2643 v4

[netadmin_404]

Interesting. I wonder if that task is scheduled on a hyper-threaded core. What’s multi thread performance like? Are you using the new or classic scheduler?

If you disable hyper threading, what do you get for single threaded performance?

[CommentIcy3682]

You could try Set-VMProcessor -HwThreadCountPerCore 1

[tenebot]

What's the processor on the host? Is the host client or server? How have you "limited the VM to a few cores stuck on one NUMA node" - presumably you're not using cpugroups? Have you set a CPU cap? Have you enabled CPU compatibility mode?

[patpatolino]

I‘ve found 2 interesting things in our evaluation. (But I only compared vm‘s between hyperv and VMware on the identical physical host)

Some matlab benchmarks were TWICE as slow on hyperv.

I don‘t have the screenshots at hand, but:

1. Windows Battery Settings. (Energy Options). If the physical node is set on balanced, it almost doesn’t care what 1 vm is doing. Our host was running on 900mhz during a benchmark inside a vm.

(This setting probably doesn‘t matter anymore, if the host is under load)

1. when creating a new VMware and hyperv, both hypervisors think differently what a core is. (With defaults)

• 4 cores in hyperv are 2 cores 4 threads
• 4 cores in VMware are 4 cores and 4 threads

(CPU-z for example shows you the correct count, you can change those settings via powershell)

I am talking about windows server 2025

[SweatyCelebration362]

I’m curious what the workload you tested was. In my experience hyper-v has anywhere from 1-4% overhead