A method of controlling a datacenter (1), for example a cloud datacenter, and a computer management system (3) for managing a datacenter comprising a plurality of servers (2) configured to execute a plurality of jobs is provided. The method comprises receiving a request to execute a job from a user (4), determining an allocated server (2) on which to execute the job, and executing the job on the allocated server (2). The determining the allocated server (2) on which to execute the job comprises: classifying the job according to its resource requirement, selecting a subset of the servers (2) that fulfill the resource requirements of the job, determining the allocated server (2) that can execute the job with a favorable energy efficiency, wherein a total resource estimate for all jobs running on the server (2) from time to time exceeds the resources of at least one of the servers (2). Accordingly, the datacenter (1) may over allocate the capacity of the physical servers (2), to overcome the overestimation of required resources by users (4).