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jedijeff
Enthusiast
Enthusiast

Another Hyperthreading discussion

I would like to clarify whether Hyperthreading is a good idea on 5.5 using a Sandy Bridge architecture. I have a 16 core host and would like to have a 16cpu VM. Only a couple very small 1cpu VM will also be on the box. The 16cpu VM can run near 50-70% peak(it is a physical box now I plan to virtualize).

I am leaning to not turn on Hyperthreading because I read about issues with it with contexts.

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MKguy
Virtuoso
Virtuoso

I am leaning to not turn on Hyperthreading because I read about issues with it with contexts.

And what are these ominous sources or what issues are there supposedly?

Back in the old Pentium Netburst days, HT wasn't very effective, but with the introduction of the Nehalem CPU architecture about 7 years ago, HT was improved a lot.

I strongly recommend to enable HT if available, as does VMware, see:

https://www.vmware.com/pdf/Perf_Best_Practices_vSphere5.5.pdf

Make sure hyper-threading is enabled in the BIOS for processors that support it.

If the hardware and BIOS support hyper-threading, ESXi automatically makes use of it. For the best

performance we recommend that you enable hyper-threading,

-- http://alpacapowered.wordpress.com
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jedijeff
Enthusiast
Enthusiast

I believe the issue was creating a vCpu count that is higher than your physical cores. Which you can do with Hyperthreading turned on.

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Alistar
Expert
Expert

Hello,

take a look at my blog post to learn a bit more on how does the HT benefit ESXi: https://vmxp.wordpress.com/2015/01/08/hyperthreading-what-is-it-and-does-it-benefit-esxi/

Basically, it helps you a lot with spreading out the workload for the hypervisor.

Stop by my blog if you'd like :slightly_smiling_face: I dabble in vSphere troubleshooting, PowerCLI scripting and NetApp storage - and I share my journeys at http://vmxp.wordpress.com/
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