It depends even more heavily on the "threading" implementation on your hardware. Some CPUs are designed to run a bunch of threads to keep the chip busy (like th

It depends even more heavily on the "threading" implementation on your hardware. Some CPUs are designed to run a bunch of threads to keep the chip busy (like the Niagara family Ultrasparcs) and others have SMT bolted on as an afterthought that mostly doesn't help (Pentium 4 "HyperThreading" or whatever Intel calls it). Then there's the AMD Bulldozer approach which is kind of between multicore and SMT, with some shared and some dedicated resources per thread. Then there's the Tera MTA style approach where you basically switch threads on every instruction to hide memory latency. Etc etc.