Hi,
I've got a number of Hyper-V hosts running and I've recently had a request to run some CPU-intensive applications on some VMs on these hosts. I look at the task manager on the host machine and see that it's basically using no CPU power at all, so I think fine, we can make some VMs and see what happens.
I created a single VM, let's call it SecretProject01. I assigned this 32 virtual CPU cores as this is the maximum allowed. This seems to work fine. In Hyper-V manager I see this machine using about 90% CPU when we use 30 cores for the CPU intensive processes. On the host machine however, I still see ~1% CPU usage and that's it. So, I think fine, let's ramp it up a bit then...
I export the VM SecretProject01 and import it again and increment the hostname and IP address by 1 to make it SecretProject02 on a different IP and spin it up. We then assign the processes to the CPU cores in the VM and it seems to run fine. However, on Hyper-V manager, I'm now seeing SecretProject01 using 50% CPU and SecretProject02 using 50% CPU. In Task manager on the host, I'm seeing ~1-2% CPU usage. Strange, but I think nothing of it and copy another VM.
Now I have SecretProject03 running as well (all on the same host) and in Hyper-V manager they are all showing running at 30% CPU usage, but the host is still showing minimal usage at ~1-3% CPU.
I'm utterly confused. Can anyone explain to me what is happening here? Is the host giving 32 virtual CPU cores to its VMs, and the fact that I've assigned 32 to SecretProject01, 02 and 03 means that it's now just sharing those 32 between the three VMs and reporting them using 30% each? I've tried reading some TechNet articles about CPU usage and Hyper-V, but my head almost exploded. I need it a bit more simply ;)
Cheers,
Andrew