Vmware Scenario’s: CPU sensitive application

Vmware Scenario’s are hypothetical situations and solutions.

This came from a post on the official Vmware forums:

– We have a ESXi server with 1 Socket 4 Core CPU with Hyper theading.  We currently have 2 VM’s with 2 vCPU’s and the performance is great.  We want to add a third VM and split up the cores among the 3 VM’s.  The only issue is the third vm will be running a really old application in Windows XP.  This application is very CPU sensitive lack of resources will cause it to crash and it’s single threaded.   How do I solve this issue?

This is fine situation that takes into account the issues discussed in this article .   There are a few questions left unanswered.

First are the first two vm’s using over 75% of their two CPU’s?

– Why do I ask this question?  Well most of the time servers are not using much of there cpu.  It seems to be the most under utilized resource in most ESXi setups.  Unless we have resource contention processor co-stop does not figure into the equation.

So we are going to assume that the processors are not 75% or more used all the time.  So co-stop is now not an issue.  Given that assumption the solution might just be as simple as reservation:

Take your new virtual machine and use CPU reservation to ensure it always get’s 100% of it’s single cpu. You single threaded application will never fail and since your not using 75% or more of the resources on your other vm’s you should never even notice.

What about hypertheading?

Well there are lots of theories on this matter an it really depends on your situation.  Unless you have over subscribed your CPU then none of the theories really come into play.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.