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

Not exactly true, this depends on the overall software architecture. There's a reason of keeping more threads than available cores in case some of the threads are suspended by the OS because they're waiting for an I/O to complete. This may be an explicit I/O invocation (such as synchronous reading from file), as well as implicit, such as system paging handling.

Actually I've read in one book that keeping the number of threads twice the number of CPU cores is is a good practice.