1. A computer-implemented method comprising: detecting an event calling for a migration of a computer workload from a source processor set to a target processor set; in response to said detecting, first allocating processes of said workload so that some of said processes are executed on said source processor set and some are executed on a second processor set of processor units; and then second allocating processes of said workload so that no process of said workload is executing on said source processor set and at least some of said processes are executing on said second processor set, said second processor set being said target processor set or being an intermediate processor set from which said workload is migrated to said target processor set.