A 3-core virtual machine

[Daringpear]

Suppose I run 2 virtual machines off of a 6800k or something similar, where each user gets 3 real cores, and 3 threads. If you want to play a game that does not allow <4 cores, would it run (because it detects that your system has 6 cores) ir not (because it detects that your virtual machine has 3 cores)? Let's assume we use unraid as the virtualization software. Also, how is software support for 3 cores?

[tt2468]

1 minute ago, Daringpear said:

Suppose I run 2 virtual machines off of a 6800k or something similar, where each user gets 3 real cores, and 3 threads. If you want to play a game that does not allow <4 cores, would it run (because it detects that your system has 6 cores) ir not (because it detects that your virtual machine has 3 cores)? Let's assume we use unraid as the virtualization software. Also, how is software support for 3 cores?

The guest vm will only see 3 cores, even though the host has more than 3.

[don_svetlio]

6 minutes ago, Daringpear said:

Suppose I run 2 virtual machines off of a 6800k or something similar, where each user gets 3 real cores, and 3 threads. If you want to play a game that does not allow <4 cores, would it run (because it detects that your system has 6 cores) ir not (because it detects that your virtual machine has 3 cores)? Let's assume we use unraid as the virtualization software. Also, how is software support for 3 cores?

Why not set 2 cores/4 threads per VM and have 2 cores/4 threads on management duty?

[thekeemo]

You can set 6 to the VM since software thinks you have 12 cores

[Daringpear]

2 minutes ago, don_svetlio said:

Why not set 2 cores/4 threads per VM and have 2 cores/4 threads on management duty?

What about a single thread? How much processing power do you need to run everything as smooth as possible?

[leadeater]

This is one area where unRAID isn't quite as nice as other hypervisors. For example on ESXi you don't manually select which cores or threads a VM will use, you can but 99.999% of the time you don't. What you do is configure a VM with how many vCPUs you want it to have and ESXi will take care of scheduling which real cores or threads actually get used, totally dynamic.

 

For example on a system with 6 cores and 12 threads you can create as many VMs configured with 12 vCPUs as you like, based on actual VM CPU load ESXi will give processor time to the VM. Creating VMs with too many vCPUs can be bad however and can even reduce performance as ESXi needs to schedule all 12 vCPUs at once even if only 1 thread in the VM is being heavily used.

 

Another example would be the same 6 core/12 thread system with 3 VMs configured with 4 vCPUs. At any one time a VM could be running its load on 4 real cores or 4 HT threads or any combination in between, it actually doesn't matter.

 

The only thing you have to be careful of in that type of CPU allocation is when the configured VMs start demanding more CPU load than you can give then you start getting CPU waits.

 

Remember unRAID can also let you share cores between VMs, the only difference is you have to select which cores or threads when you create the VM. Sharing cores is fine as long as the demand is not higher than you can give, if each VM has all 6 cores assigned but the game is only using 3 threads then two VMs can have effectively the full performance they can possibly get.