Scott Drummonds on Virtualization

Optimizing vSphere for Hyper-threading


VMware’s Jeff Buell has been looking into High Performance Computing (HPC) in support of a new addition to the office of the CTO.  Jeff just posted an article on VROOM! showing outstanding memory bandwidth in vSphere virtual machines.  No one should be surprised by this–virtual machine memory bandwidth has rarely been a problem.  But Jeff did discuss a advanced configuration parameter that should pique everyone’s curiosity: NUMA.preferHT.

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How Many Virtual CPUs Per VM?


Virtual machine sizing is a tricky issue for many VMware administrators. It is important to find the right number of virtual CPUs to maximize application performance and minimize wasted CPU cycles. The optimal number of vCPUs can never be easily identified. But I can offer a few suggestions to help get this number right.

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vSphere 4.0, Hyper-Threading, and Terminal Services


I recently wrote a blog article detailing Hyper-Threading (HT) and its effect on vSphere.  An astute reader pointed out, a recent update to Project VRC‘s terminal services analysis suggests disappointment with HT on vSphere.  We spent a lot of time looking at those results to understand why they contradicted the body of performance data, which show HT offering 10-30% gain on vSphere. What we discovered led us to create a vSphere patch that would allow users to improve performance in some benchmarking environments.

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Hyper-Threading on vSphere


I continue to receive many questions from our customers on the expected performance gains of the new version of Hyper-Threading in Intel’s Core i7 processors. The answer requires a little bit of discussion on Hyper-Threading, a little bit on ESX, and comes with some performance data. If you are still interested, read on.

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Inaccuracy of In-guest Performance Counters


Every couple of months I receive a request for an explanation as to why performance counters in a virtual machine cannot be trusted.  While it is unfairly cynical to say that in-guest counters are never right, accurate capacity management and troubleshooting should rely on the counters provided by vSphere in either vCenter or esxtop.  The explanation is too short to merit a white paper but I hope a blog article will serve as the authoritative comment on the subject.

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Four Things You Should Know About ESX 4's Scheduler


[This is the last re-post of old community content.  But this content is important enough to be worth a re-post.]

I spend a great deal of time answering customers’ questions about the scheduler. Never have so many questions been asked about such an abstruse component for which so little user influence is possible. But CPU scheduling is central to system performance, so VMware strives to provide as much information on the subject as possible. In this blog entry, I want to point out a few nuggets of information on the CPU scheduler. These four bullets answer 95% of the questions I get asked.

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