Wasted resources in gang scheduling

Gang scheduling (the scheduling of a number of interacting threads to run simultaneously on distinct processors) can leave processors idle if the sizes of the gangs do not match the number of available processors. Given an optimal offline algorithm it is shown that the wasted processing power can range from 0% to 50%, depending on the distribution of gang sizes. Focusing on the uniform and the harmonic distributions, rather than worst-case distributions, it is shown that if there are no restrictions on how the processors are partitioned, these distributions cause no waste with an offline algorithm but a waste of 20% to 37% for online algorithms. Using the distributed hierarchical control scheme, which is similar to buddy systems for memory allocation, a waste of 10% to 20% should be expected for offline algorithms, and 21% to 51% for online algorithms