We are benchmarking existing Java programs. They are threaded applications designed to benefit from multi-core CPUs. We would like to measure the effect of the number of cor
It's called setting CPU affinity, and it's an OS setting for processes, not specific to Java.
On Linux: http://www.cyberciti.biz/tips/setting-processor-affinity-certain-task-or-process.html
On Windows: http://www.addictivetips.com/windows-tips/how-to-set-processor-affinity-to-an-application-in-windows/
On Mac it doesn't look like you can set it: https://superuser.com/questions/149312/how-to-set-processor-affinity-on-os-x