Number of processor core vs the size of a thread pool

Question

Many times I\'ve heard that it is better to maintain the number of threads in a thread pool below the number of cores in that system. Having twice or more threads than the numbe

Answer 1

That's not true, unless the number of threads is vastly more than the number of cores. The reasoning is that additional threads will mean additional context switches. But it's not true because an operating system will only make unforced context switches if those context switches are beneficial, and additional threads don't force additional context switches.

If you create an absurd number of threads, that wastes resources. But none of this is anything compared to how bad creating too few threads is. If you create too few threads, an unexpected block (such as a page fault) can result in CPUs sitting idle, and that swamps any possible harm from a few extra context switches.