I am running an extreemly CPU intensive multi-body simulation which lend itself nicely to parallel processing. We have run several tests with the same simulation using a single-threaded compilation and a multi-threaded compilation. We have run the same simulation with the hyper-threading on and off. Here are the results:
The 12-body simulation on the dual-dual core Xeon machine runs about 70% faster when using the multi-threaded compilation compared to the single-threaded compilarion.
When we turn hyper-threading on, the execution of the multi-threaded compilation slows down about 15%. In this CPU intensive simulation, the 8 processor threads fight for CPU time and only average about 50% CPU time for each hyper-thread. With the hyper-threading off, the same simulation uses all four CPUs at almost 100% throughout the simulation.
So, we are are turning hyper-threading off because most of our processor time is spent running these CPU intensive simulations.