VMWare ESXi and IRQ balancing

I've only read about this topic a handful of times. I found an article at www.vmguy.com here that sums up the consensus on this HT issue (direct from the article):

There are pros and cons to using HT in ESX.

Pros

• Better co-scheduling of SMP VM’s

  Hyperthreading provides more CPU contexts and because of this, SMP VM’s can be scheduled to run in scenarios which would not have enough CPU contexts without Hyperthreading.

• Typical applications see performance improvement in the 0-20% range (the same as non-virtualized workloads).

Cons

• Processor resources are shared with Hyperthreading enabled

Processor resources are shared such as the L2 and L3 caches. This means that the two threads running on the same processor compete for the same resources if they both have high demand for them. This can, in turn, degrade performance.

All things considered, it is difficult to generalize the performance impact of Hyperthreading. It is highly dependant on the workload of the VM. One additional point is that you can always utilize the CPU min and max values on a per-VM or Resource Pool basis to reserve certain amounts of CPU for your most critical workloads. As with the majority of performance items I enounter, test, test, test. Try out the workloads and see what works the best on the hardware you have available.

Again, this is directly from the article. I'm not certain that HT is worth it as I too use AMD Opterons so I can't speak from experience.

You have to pay for vSphere with its various modules and extra features but not to use the vSphere Client to connect to a free ESXi.

I think where you may be getting the license message from is although ESXi is free, you still need to request a free license key from VMWare.

Login to your ESXi box with vSphere Client and go to Configuration -> Licensed Features -> Edit.

If you are set to evaluation mode, that is what you are getting the license warning from.

VMWare should have emailed you a license key when you signed up on their website to download ESXi. If not, you can go through the download steps again and the license key should be on one of the pages.

For me, if I go to https://www.vmware.com/products/esxi/ hit Download, login with my free VMWare account, then on the page with all of the download links, at the top of the list is my ESXi License.

The reason you are seeing the license message about vSphere is that in the Evaluation mode, some of the extra features that are only available with vSphere are enabled, once you enter a free ESXi license, those will be disabled and you won't get prompted anymore.

Also, you can use the vCenter Converter in the standalone mode (runs off of your workstation) for free with ESXi. This tool is immensely useful for moving VMs on and off of ESXi. http://www.vmware.com/products/converter/.