Performance Monitoring

An apparatus comprises at least one memory system component configured to handle memory transactions for accessing data. The apparatus also comprises performance monitoring circuitry configured to determine an interference-specific performance value indicative of a performance impact associated with a given memory system component handling at least one interfering memory transaction, where handling of an interfering memory transaction comprises use of memory system resource which would have otherwise been available for handling at least one affected memory transaction. The performance monitoring circuitry is configured to make the interference-specific performance value available to a resource control agent.