For each thread of a computer program to be executed on a multiple-processor computer system, an affinity identifier is associated to the thread by the computer program. The affinity identifiers of the threads denote how closely related the threads are. For each thread, a processor of the multiple-processor computer system on which the thread is to be executed is selected based on the affinity identifiers of the threads, by an operating system being executed on the multiple-processor computer system and in relation to which the computer programs are to be executed. Each thread is then executed by the processor selected for the thread.