Re: hyperthreading being a terrible idea in general
which doesn't help much performance much if any for most workloads
This is very application dependent. If you're getting L3 cache misses then the HyperThreading helps, it's just doing a context switch in HW. If your application is clever enough not to spend most of its time waiting to get data from memory then HW multithreading won't work. I seem to remember that for the TPC-C benchmark it made about a 50% difference when you enabled the HyperThreading, but then TPC-C is a bloody stupid app. Mind the biggest problem with had with TPC-C and the multithreading was that for the CPU involved a certain DB vendor doubled the license fee, so you got a 50% speed up for a 100% cost up.