CPU Entiltiement problem in VM Host

[Mahesh Babbar]

I stucked up with a problem on design of HP Integrity VM. Here i have a BL870C with 2 dual core CPU and 32GB memory. We have to design the VMs in such a way that all with get 50% of CPU resources as guarantee. So we changed the entitilment of machines to 50%,and created such 8VMs. But now the thing is that the 8th machine is not starting because of lack of cpu resources.

1/ So may i know How can we identify how much CPU resource should need for VM host functioning, so that i can restrict the allocation of CPU resource to VM guest.

2/ May i know the minimum amount of CPU needed for VM host.

3/ May i know how to restrict a VM Guest from using full CPU resources.

Means, By setting entitlement ,we can guarantee this much amount of CPU resourec to that Guest. But on some case the VM guest CPU utilization increased very much and it effected other VM also. How can we set a maximum of CPU usage for each VM guests


Thanks in advance for your valid suggetion for our design

[Dennis Handly]

>2 dual core CPU

Make it simple for us dummies, how many cores to you have, 4 or 2?

How hard is it to change to 40%, to see if there is some overhead?

[Torsten.]

Hi,

regarding the entitlement you should review the manual section about this:

section 3.2.4 Entitlement in current version 4.0 manual.

At least in this version you can also set a maximum other than 100%, e.g.

> hpvmmodify -p 1 -e 10:50

> hpvmstatus -r
[Virtual Machine Resource Entitlement]
[Virtual CPU entitlement]
Percent Cumulative
Virtual Machine Name VM # #VCPUs Entitlement Maximum Usage Usage
==================== ===== ====== =========== ======= ======= ================
hpvm01 1 1 10.0% 50.0% 0.0% 0

[Mahesh Babbar]

I am having total 4 cores and i required to create 8 VM with 40 or 50%, Please may i know how much cpu resources should be reserved for VM Host operation.Do we have any formula for this?

[Eric SAUBIGNAC]

Bonjour WWDC,

You should work in a relative way to set entitlement. Just a simple example : suppose you have one host with one cpu 1P/1C. Suppose you have 2 VM, with 1 vCPU each. Suppose you want that under CPU pressure one VM get 25% of physical CPU and the other one 75%. Following your approach I guess you would give an entitlement of 25% to VM 1 and 75% to VM 2. Right ?

The problem is that once a VM is started you will not be able to start the second one, because you don't have 100% CPU free for VM usage : when starting a VM, HPVM checks that it will be able to give to the VM the requested entitlement. As far as I know there is no formula to compute how much the host needs, no more formula to compute CPU overhead. You can try to give 24% to one VM, 74% to the other one, but you are not sure that it will always work.

In a relative approach, you say that the second VM will have 3 more times power than the first one. So give the lowest entitlement to VM 1, that is 5%, and 15% to the second one. In case of CPU pressure from both VM, the remaining free cpu will be shared between VM according to the ratio 5/15 wich is the same than 25/75.

In your case, if I understand correctly your needs, it seems that you want to give half a core to each VM. Right ? May be the more simple way to do that is to give one vCPU and a 5% entitlement to each VM. If all of the 8 VM experiments CPU pressure at the same time, each VM should get around half a core, depending on CPU used by host itself.

As said torsten, you can now set with HPVM 4.0 a capping value to limit CPU usage of each VM.

If you want to manage more finely your VMs you can also try gWLM : http://docs.hp.com/en/vsemgmt/gwlm.html

Regards

Eric

PS : Je viens de consulter ton profil et je t'invite donc a jeter un oeil a l'URL http://forums13.itrc.hp.com/service/forums/helptips.do?#28 ;-)

[likid0]

4 cpus - 8 vms

Give them 5% entiltenment ,and you will be fine