Benchmarking and accounting for the (private) cloud

During the past two years large parts of the CERN batch farm have been moved to virtual machines running on the CERN internal cloud. During this process a large fraction of the resources, which had previously been used as physical batch worker nodes, were converted into hypervisors. Due to the large spread of the per-core performance in the farm, caused by its heterogenous nature, it is necessary to have a good knowledge of the performance of the virtual machines. This information is used both for scheduling in the batch system and for accounting. While in the previous setup worker nodes were classified and benchmarked based on the purchase order number, for virtual batch worker nodes this is no longer possible; the information is now either hidden or hard to retrieve. Therefore we developed a new scheme to classify worker nodes according to their performance. The new scheme is flexible enough to be usable both for virtual and physical machines in the batch farm. With the new classification it is possible to have an estimation of the performance of worker nodes also in a very dynamic farm with worker nodes coming and going at a high rate, without the need to benchmark each new node again. An extension to public cloud resources is possible if all conditions under which the benchmark numbers have been obtained are fulfilled.