I cannot choose specific CPU type

[Jim@@@]

My CPU is i7-4770, but when I choose Haswell as the Processor type, it would not boot up, so I am using "Default (kvm64)" under VM setting, and it works OK.

I have two questions:
1. Does Proxmox optimize the VM depending on the CPU type? Or it does not make much difference if I left it as "Default"?
2. Haswell is a 4-core CPU, and it has hyper thread. Does that mean I can assign up to 8 cores? I only have this CPU. What is the best practice? Best to leave 1 for the proxmox itself, and use the rest of the 7 cores for VMs?

Please advise.

 

[udo]

Hi,
depends on your usage - if you have an cluster with (slightly) different cpus you need an subset to use live-migration.
For many usages is kvm64 an good choice. If you need cpu-support which kvm64 don't have (like aes) "host" can be the right one.

HT isn't visible for the client and use one core for pve don't work either - except you start with pinning.
But this is normaly no problem - you can easily overcommit your cpu (but don't give one guest more than HT-cores you have).

Udo

 

[Jim@@@]

Thank you, Udo.
I leave the KVM64 as is, but I did not quite understand the last two lines. To make it simple for me, how many total cores can I assign to VMs?
4 or 3? 8 or 7?

 

[udo]

Hi,
if you don't disabled HT in the bios max. 8 for an (or more) VMs.

Depends on the workload of the VM-guests you can overcommit the cpu like:
3 VMs with 2 cores
2 VMs with 4 cores
1 VMs with 6 cores
1 VMs with 8 cores

If your VMs do "numbercrunching", this will work not really good of course.
For normal usage the cpu isn't the bottleneck - mostly IO, then mem, cpu...

Udo

 

[Jim@@@]

I see. So with HT, you double the number of CPU core, and that is how many you can assign and distribute them.
I do not understand why, but the number you gave me tells me that it is not a good idea to assign odd number of CPUs to a VM. Maybe it is due to the nature of HT.

Anyway, thank you so much! I really appreciate it.

 

[udo]

I see. So with HT, you double the number of CPU core, and that is how many you can assign and distribute them.
I do not understand why, but the number you gave me tells me that it is not a good idea to assign odd number of CPUs to a VM. Maybe it is due to the nature of HT.

Anyway, thank you so much! I really appreciate it.

Hi,
you can also use an odd number of CPUs... it's should only shows that you can overcommit the cores.

Udo

 

[Jim@@@]

Udo, thank you again for your comment!