The commissioning of CMS computing centres in the worldwide LHC computing Grid

The computing system of the CMS experiment uses distributed resources from more than 60 computing centres worldwide. Located in Europe, America and Asia, these centres are interconnected by the Worldwide LHC Computing Grid. The operation of the system requires a stable and reliable behavior of the underlying infrastructure. CMS has established a procedure to extensively test all relevant aspects of a Grid site, such as the ability to efficiently use their network to transfer data, services relevant for CMS and the capability to sustain the various CMS computing workflows (Monte Carlo simulation, event reprocessing and skimming, data analysis) at the required scale. This contribution describes in detail the procedure to rate CMS sites depending on their performance, including the complete automation of the program, the description of monitoring tools, and its impact in improving the overall reliability of the Grid from the point of view of the CMS computing system.