Abstract. Cache affinity between a process and a processor is observed when the processor cache has accumulated some amount of the process state, i.e., data or instructions. Cache affinity is exploited by OS schedulers: they tend to reschedule processes to run on a recently used processor. On conventional (unicore) multiprocessor systems, exploitation of cache affinity improves performance. It is not yet known, however, whether similar performance improvements would be observed on multicore processors. Understanding these effects is crucial for design of efficient multicore scheduling algorithms. Our study analyzes performance effects of cache affinity exploitation on multicore processors. We find that performance improvements on multicore uniprocessors are not significant. At the same time, performance improvements on multicore multiprocessors are rather pronounced.