topic Does VMWARE Workstation support CPU affinity? in VMware Workstation Pro Discussions

Does VMWARE Workstation support CPU affinity?

vitaly_il1 — Fri, 02 Oct 2020 09:42:42 GMT

I have a box with 2 CPU socket (2*40 cores), running CentOS. I'd like to assign the 1st CPU socket for VMs. Is this doable with VMWARE Workstation?

TIA, Vitaly

Re: Does VMWARE Workstation support CPU affinity?

scott28tt — Fri, 02 Oct 2020 10:35:18 GMT

There's nothing in Workstation itself which will do that.

I found this hack which involves running a script once you have all your VMs running, to tell the Windows host OS where to run the processes which support each VM: https://houseofbrick.com/troubleshooting-vmware-workstation-at-100-cpu/

Re: Does VMWARE Workstation support CPU affinity?

vitaly_il1 — Fri, 02 Oct 2020 10:59:47 GMT

Thank you! Sorry, I didn't mention that I have CentoOS as host OS.

Re: Does VMWARE Workstation support CPU affinity?

bluefirestorm — Fri, 02 Oct 2020 12:48:11 GMT

If the host machine can support NUMA, it is better to turn on the NUMA in the host UEFI/BIOS.

From the log, it appears VMware Workstation can see the NUMA nodes.

| vmx| I125: NUMA node 0: 15973MB, cpus 0x00000f0f 0x00000000 0x00000000 0x00000000

| vmx| I125: NUMA node 1: 16101MB, cpus 0x0000f0f0 0x00000000 0x00000000 0x00000000

But the VM will not see the NUMA architecture. I don't think Workstation Pro can take advantage of NUMA directly. For that you need ESXi. ESXi also allow you to assign affinity.

Running Prime95 stress test in a 6 vCPU Windows 10 VM in an Ubuntu 18.04, NUMA enabled 2 CPU sockets host and Workstation Pro 15.5.x, the System Monitor on the host will show 100% for 6 CPUx. Sometimes one host core/thread will flip to a different host CPU core/thread but it will stay at 100% for some time. It does not keep jumping around.

Probably the largest determinant whether a vCPU will be "sticky" to a physical CPU core/thread depends on execution profile of the application(s) running in the VM. If the application causes a lot of VM-EXITs (such disk I/O or network I/O), assigning affinity may not add so much to performance.

Using the Prime95 stress test example, it is compute intensive so it is unlikely to have frequent VM-EXIT so it can be somewhat sticky to a host core/thread unless it needs to read/write memory not in cache or read disk/IO and thus causing VM-EXIT and possible switch to a different core after a VM-ENTRY. I am assuming with NUMA turned on and the somewhat sticky vCPU-host CPU association, it is better than having non-NUMA.

Re: Does VMWARE Workstation support CPU affinity?

gbohn — Fri, 02 Oct 2020 15:37:32 GMT

Just for reference, I don't know if this still works, but Tie the VM to a cpu? mentions setting .vmx affinity values like

processor0.use= "TRUE"

processor1.use= "FALSE"

etc.