Impact of enabling hyperthreading

[dbadhani]

I read different things across posts so a little confused about the impact of enabling HT.

Lets say I have an ESX host with the following specs:

2 Physical CPUs ( Intel Xeon x5550, quad core), HT disabled.

I create a VM, and assign it 1 vcpu. So it will be allocated 1 logical vcpu ( or in other terms 1 HEC) from a pool of 8.

So assuming this the only VM running, and its running to MAX, it should be using approx 12.5% of CPU resourse.

Now if I enable HT (Both in bios and vsphere), will it get 1 logical vcpu from a pool of 16 ? In other words, does it mean it will get approx 6.25% CPU resources? It will imply increasing vpcu allocation to 2 in that case.

Thanks,

Devendra

[AntonVZhbankov]

>Now if I enable HT (Both in bios and vsphere), will it get 1 logical vcpu from a pool of 16 ? In other words, does it mean it will get approx 6.25% CPU resources? It will imply increasing vpcu allocation to 2 in that case.

ESX is HT aware and won't treat HT cores as physical cores. So you can enable HT and gain some performance boost, about 10-15%.

---

MCITP: SA, MCTS Hyper-V, VCP 3/4, VMware vExpert

http://blog.vadmin.ru

[dbadhani]

Thanks for the quick response.

Let me rephrase my question. If I had allocated 1vcpu to a VM in a non-HT host, when I move it to a ESX host with HT enabled, should I double the number of vpcus to get the same performance as the original?

Thanks,

Deven

[mcowger]

No - it will retain the same performance (assuming the CPU is similar, of course).

--Matt

VCP, VCDX #52, Unix Geek, Storage Nerd