Hi,

I had the course for VCP but not yet taken the exam. But im struggling in explaining an question from my colleagues.

If you install an 2008R2 server with 2 CPU, why dosent it improve performance if you up this to 4 CPU ? It gets even worse ?

As i took the course we discussed this thing, but i can not say that i actually understood the answer.

This has to do with Waiting time on CPU. How to set an CPU to use 1 whole CPU singlehanded and share with another server ? Is the best practice to use MHz reservation or use shares (Set one server to be 4000/4000 shares f.ex)

Could someone elaborate on this topic and help me better understand ?

Regards

>> If you install an 2008R2 server with 2 CPU, why dosent it improve performance if you up this to 4 CPU ? It gets even worse ?
How many VMs / vCPUs are you running on the host? How many physical CPU cores does the host have? It sounds like ESXi having trouble scheduling CPU resources. If you're seeing high wait times that might be the case.

>> How to set an CPU to use 1 whole CPU singlehanded
Are you looking to dedicate a CPU core to a vCPU?

>> Is the best practice to use MHz reservation or use shares (Set one server to be 4000/4000 shares f.ex)
It'll depend on your scenario. A reservation guarantees that your VM will get the resources it needs. Shares impact how much resources a VM will get when a resource is low. If you have plenty of CPU shares don't play a role.

Hi,

How many VMs / vCPUs are you running on the host? How many physical CPU cores does the host have? It sounds like ESXi having trouble scheduling CPU resources. If you're seeing high wait times that might be the case.
> The host is Quad CPU so it has 4 cores. It's running 5 VM. How to best check if the wait time is high ? What the difference between CPU wait and CPU Ready time ?

Are you looking to dedicate a CPU core to a vCPU?
> Yes Too see if this improve performance (Vm that runs many small Perl scripts)

It'll depend on your scenario. A reservation guarantees that your VM will get the resources it needs. Shares impact how much resources a VM will get when a resource is low. If you have plenty of CPU shares don't play a role.
> What i am trying to achive is to get better performance from my VM that is running all these Perl scripts. I wont it to respond faster and reduce amount of time it takes.

regards

Take a look at the performance tab for the VM in the vSphere client. Look at the CPU performance counters:
Ready - time that the VM needed CPU but couldn't get it
Wait - time that the VM got CPU, but didn't need it
Demand - what the VM wanted if there was no CPU contention

You won't be able to set affinity with just 4 CPU cores if the VM has 4 vCPUs. If you drop it down to 2 CPUs, then look at the VM properties (Edit Settings > Resources > Advanced CPU > Scheduling Affinity