CPU Reservation Upper Limit?

[Rhidian]

Hi,

Does anyone know how the upper limit for the CPU reservation is calculated as it doesn't seem to correspond to the CPU summery etc, additionally does anyone have any input on the best way to guarantee say 1/16 of a core share?

[mittim12]

I'm not sure I understand the question completely.  If you don't specify a CPU limit then the machine would be limited by the number of vCPU assigned to the VM.

[Rhidian]

Apologies for not being clear.

On my host the summery page gives the CPU capacity as 16 x 2.4 GHz made up from 4 sockets with 4 cores per socket and HyperThreading set to inactive, if I look at an example virtual machine under the resources TAB I can assign a max CPU reservation of 208176MHz how is this number calculated?

4 x 4 = 16

16 x 2400 = 38400

38400 - 208176 =  -169776

If I check the cluster summery the total CPU resources is shown as 307GHz based on 8 hosts and 128 processors, how is this number calculated as the resource allocation TAB shows a total capacity of 275520MHz?

In addition to the above I would like some idea's on the best way to restrict a virtual machine to 1/16th of a processor, is it to add a reservation per CPU etc?

[mohdbaqari]

This can't happen. You can't reserve CPU resources more than whats physically available. I have also checked this in my lab and confirmed it. Also, to restrict CPU per VM you need to use limits and not reservations.

[Rhidian]

I have answered my own question the limit seems to be coming from the parent cluster minus any reservation as seen on the resource allocation TAB although the summery of the cluster shows different numbers is there a document or URL detailing where and what these metric are calculating?

[mohdbaqari]

- I am working in ESXi 5 and can till that this is not 100% true.

- Although the max number in the limit field will show the total CPU of the cluster, you won't be able to set the limit beyond the value of the host.

[AndreTheGiant]

Are you working with VM properties of at resource pool level (this is not 100% clean)?

Also you are talking about reservation and limit that are two different concept: reservation is the minumum resource guarantee, limit is the maxium usable resources.

About the CPU HT does not change how is calculated, you must consider the phisical core speed and this become the virtual CPU (or virtual core in vSphere 5) speed. The resource in MHz is a total in a VM.

[Rhidian]

I'm trying to make sense of all the numbers to be honest but at the VM level the upper CPU reservation is being derived from the cluster CPU resources minus any reservation and not the host CPU resources, additionally the information on the summery page of the cluster is different to what is displayed on the resource allocation TAB i.e. 307GHz and 275520 MHz.

[AndreTheGiant]

The upper level is not relevant, because you have another hard-limit: the number of vCPU (x the number of vCores).

You cannot go higher than this limit (unless you add other vCPU).

Same is for RAM...