During the Monster VM Design Panel at VMworld in San Francisco and Barcelona our panel was asked about vNUMA and the impact on performance of various different settings including modifying the number of cores per virtual socket. Mark Achtemichuk (Mark A for short) has written an article on the VMware vSphere Blog taking a look at this with some great test data to go with it. I’ll give you some highlights and then you can check out the actual article for yourself.

Mark’s article goes into the history of the Cores Per Socket (Number of vCPU Cores per Virtual CPU Socket) in a bit of detail. It was really meant for licensing, not performance. As Mark shows in the article for best performance you should configure your VM’s to be wide and flat (1 vCPU per vSocket), and let vSphere and vNUMA do it’s thing to optimize performance. Except in the case where you need to configure it differently for licensing reasons.

Many times during the Monster VM Panel Discussions we were asked about NUMA and the benefits or penalties of different configuration options. Especially around vNUMA and crossing NUMA boundaries. I would like to put your mind at ease. If you’re VM is right sized, and it actually needs lots of vCPU’s and Memory, then crossing a NUMA boundary, regardless of the penalty, is much more beneficial for performance than not having the necessary resources at all. This also assumes that the hosts aren’t too aggressively overcommitted. The reason for this is that access other resources (such as network and disk) takes a lot longer than it does to make a remote memory / processor call. Plus vSphere is very intelligent when it comes to scheduling your VM’s and generally does a very good job of optimizing for performance without you needing to tweak anything. Aside from following some common sense best practices, such as sizing VM’s so they are easily divisible by the size of your NUMA nodes, you don’t usually have to tweak too much.

If you don’t know what I’m talking about, i.e. you’re not sure what NUMA is check out this WikiPedia Article on Non-Uniform Memory Access. NUMA is also often referred to as Non-uniform Memory Architecture.

To get the full low down on Cores Per Socket and vNUMA check out Mark A’s Article – Does corespersocket Affect Performance?

Final Word

For those of you going to vForum in Sydney and Singapore you’ll have your opportunity to attend the Monster VM Panel in person and ask your panelists all of the toughest Monster VM related questions you’ve got. I hope to see a lot of you there. #vForumAU #vForumSG

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This post first appeared on the Long White Virtual Clouds blog at longwhiteclouds.com, by Michael Webster +. Copyright © 2013 – IT Solutions 2000 Ltd and Michael Webster +. All rights reserved. Not to be reproduced for commercial purposes without written permission.