Impossible to activate hyperthreading on ESXi 6.5 hosts

[DariuszNowara]

Hi experts,

    I have a following riddle. I need to enable Ht on all the hosts in my environment. It is enabled on the HP servers itself (verified in the BIOS settings and there is a message during the boot that says it is enabled). the VMkernel.Boot.hyperthreading advanced property is set to $True. Whenever I go to the Settings -> Hardware -> Processors it says HT: Disabled. I set it to Enabled (there is a message next to it saying, that "Changes will not take effect until the host is restarted") and click OK. there us a task showing up at the bottom named "Enable Hyperthreading" which completes successfully and nothing changes - it remains "Disabled" and in the summary tab "Inactive". The reboot of the host doesn't change anything in this respect. Any clues here? Where to look for any related logs? Thank you in advnce for help!

[rajen450m]

Hi DariuszNowara​

Please update the firmware of the hosts and try, we had a similar issue, resolved after updating firmware.

Regards,

[bluefirestorm]

Perhaps simplest explanation is that the CPU that is installed does not have Hyperthreading.

What is the CPU inside the server?

Not all Intel Xeon CPUs have hyperthreading. This is a list of Intel Xeon that does not have hyperthreading.

https://ark.intel.com/Search/FeatureFilter?productType=processors&HyperThreading=false&FamilyText=In...

[DariuszNowara · Accepted solution]

Gents,

    It is HPE DL380 Gen 10. As mentioned it does have the HT enabled, which can be checked in the BIOS. In the end I found a solution after a lot of digging - disabling the VMKernel.Boot.hyperthreadingMitigation advanced option made it possible to tick the box. It is a little surprising to me as from the description of the setting it does not switch off the HT for good but only restricts it's use in a certain way

[NHarris]

SOLVED

So slightly off-subject target (and posting to an old thread) I have a pair of old VSphere managed ESXI 5.5 lab hosts on a tyan motherboards

Tyan S5510 Intel(R) Xeon(R) CPU E3-1230 V2 @ 3.30GHz; sockets:1; cores:4; logical:8; BIOS V2.01; VMware ESXi, 5.5.0, 9919047

after a power loss while hosts were up: one of them dropped to sockets:1; cores:4; logical:4  Checked BIOS/CMOS everything correct.  host configs had the same message in vsphere web and client:  Hyperthreading enabled with "Changes will not take effect until the host is restarted."  cycled a couple times enabling and disabling the flag.  even reseating cpu, ram, cards, and blew the dust out - but could not re-enable the logical count to 8. 

I tried unchecking the VMKernel.Boot.hyperthreadingMitigation flag on the host per DariuszNowara and the logical returned to 8 after a reboot.  Seems this is something in the kernel that's been around for a while but never surfaced enough to address.

Maybe noteworthy to someone so I'll add that the other host, the one of the pair which was the unaffected host after the power loss was Tyan S5510 Intel(R) Xeon(R) CPU E3-1230 V2 @ 3.30GHz; sockets:1; cores:4; logical:8; BIOS V2.01; VMware ESXi, 5.5.0, 3248547