default number of threads should be number of physical cores, not logical

[grr]

the default number of threads should be set to the number of physical cores, not logical cores. If you have a 4 core machine with hyperthreads, the default number of threads is 8. This is actually a bit slower than if 4 threads were used, since each core is already fully utilized and the extra 4 threads incur extra context switching.

[cculianu]

Yeah you're right. I'll look at modifying this code. Not sure if go provides a platform-neutral mechanism to detect this but I'll lookk into it (it's been a while since I programmed in go).