SMT (Hyper-threading) on AMD EPYC CPUs

[DCollette]

We recently replaced our aging SimpliVity 380 Gen 10 Intel-based system with a new SimpliVity 325 Gen 11 AMD-based system. Everything is running fine but I recently noticed that the VM CPUs are not hyper-threaded (SMT in AMD parlance). Hyper-threading is enabled in VMware and I see that HPE supports SMT in the server BIOS.

Is there any way to determine if SMT is enabled in the server BIOS without shutting it down and going into the RBSU? If SMT is disabled, is it recommended to enable it or leave it disabled?

Thanks,

Doug

[Sahana_S]

Hello @DCollette ,

You need to reboot the server for BIOS settings to be viewed, applied and reflected.
To determine if SMT is enabled in the server BIOS and to enable or disable it:

1. From the System Utilities screen, select System Configuration > BIOS/Platform Configuration (RBSU) > Processor Options > AMD SMT Option.
2. Select one of the following:

   • Enabled—Each physical processor core operates as two logical processor cores. Enabling this option can improve overall performance for applications that benefit from a higher processor core count.

   • Disabled—Each physical processor core operates as one logical processor core.

3. Save your setting.

If your workload benefits from more logical cores, enabling SMT is generally recommended.

If you feel this was helpful, please click the KUDOS thumb below. Also consider marking this as an "Accepted Solution", if the post has helped to solve your issue.

Thanks and Regards,
Sahana S

[DCollette]

Thanks for your answer, Sahana. I knew I could enable or disable SMT from within the BIOS but was hoping there was a way to check the status without having to migrate all the VMs off a host to enter the BIOS. Guess the answer is you can't.

Is there an official recommendation from the SimpliVity team regarding whether SMT should be enabled or disabled? If it's not enabled, I don't want to cause any problems by enabling it if it's not recommended.

Thanks,

Doug

[Sanika · Accepted solution]

Hi @DCollette 

Yes, you can't check SMT status from BIOS without rebooting.
But in my opinion, you may confirm it from within ESXi using "esxcli hardware cpu list". You may look for "Threads per core: 2" - that means SMT is enabled. No VM migration needed.

There’s no explicit official recommendation from HPE SimpliVity that mandates SMT be enabled or disabled across all deployments.
However, SMT is supported and commonly enabled in HPE SimpliVity environments. When enabled and configured correctly, SMT can improve the performance of virtualized workloads on HPE SimpliVity by allowing more efficient use of processor resources.

Unless you’re running latency-sensitive workloads or have strict security policies that require disabling SMT, I think enabling it is generally safe and beneficial.

If you feel this was helpful, please click the KUDOS thumb below. Also consider marking this as an "Accepted Solution", if the post has helped to solve your issue.

Regards,
Sanika

[DCollette]

Hi Sanika,

Thanks very much for answering both of my questions. I determined that SMT is enabled on both of our SimpliVity nodes, which is what I was hoping for.

Thanks again for your assistance.

Doug

[Sanika]

Hi @DCollette 

That's good to know! Happy to help in any way I can.

Regards,
Sanika.