Hyperthreading benefits & drawbacks in ESXi 5.5 server

[ManivelR]

Dear All,

I have some doubts on  hyperthreading in ESXi 5.5 server?

I have 8 sockets * 10 cores per socket HT enabled.

which means 80 PCPU and logical will be 160 processors(after HT).

My question is,can i use 32 vCPU each for five virtual machines? i.e., 160 VCPU(total)

HyperThreading: What is it and does it benefit ESXi? Which scenario can we use over provisioning?

Does ESXi Benefit from HyperThreading?

Note:- i heard that "never assign more vCPU's than the number of physical cores your host has".

Any feedback is highly appreciated.

[dhanarajramesh]

1) HT enabled Logical CPU would not give you 100% performance as Physical CPU which means if your 80 PCPU (each of them) might able to do processing 100% then when you enable HT on those PCPU, it would give extra 15%~20% performance that would be 115% or 120% of total performance. so as a design practice do not calculate logical CPU as VCPU.

2) My question is,can i use 32 vCPU each for five virtual machines? i.e., 160 VCPU(total)    you should always calculate your 1 PCPU = 1 VCPU as 80 and when you are provisioning CPU, please keep in mind about the NUMA architecture of Your system. 

3) as best practice and depends on our work load, we have different best practices. 1) for DB workload and critical work load, we are over provisioning as 1PCPU = 2 VCPU ratio. for normal workload we are provisioning as 1 PCPU= 4 or 5 ratio.