A method and system for providing performance estimations for a specified power budget provides an indication of the impact on processing performance when closed-loop power/performance control is employed to meet the specified power budget. A workload, which may be the actual workload, or a test workload is run to determine actual power consumption at intervals during the execution of the workload. The power values are examined and if they exceed the specified budget, which may be one of multiple possible budget values, an estimate of the amount by and duration for which the closed-loop power/performance control would have to reduce the performance of the system for each interval in order to provide an estimate of actual performance for the budgetary level(s). The estimate is informed by tests of the workload at each power/performance level to provide a non-linear estimate of the relationship between performance and power for the particular workload.
