Cloudtidings.com

In a recent update of the phase II of Project VRC, VMware was behind Hyper-V R2 and XenServer.

Although XenServer and  Hyper-V R2 performed nearly identical, Vmware get behind by 10%-30%. VMware responded to the findings  and wrote a fix for VMware vSphere 4.0 to try to close the gap :

 "…What we discovered led us to create a vSphere patch that would allow users to improve performance in some benchmarking environments."

There are three specific conditions that can excite this condition:

1. A Xeon 5500 series processor is present with Hyper-Threading enabled,
2. CPU utilization is near saturation, and
3. A roughly one-to-one mapping between vCPUs and logical processors.

In this scenario, VMware vSphere favors fairness over throughput and sometimes pauses one vCPU to dedicate a whole core to another vCPU, eliminating gains provided by Hyper-Threading