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Power is arguably the critical resource in computer system design today. In this work, we focus on maximizing performance of a chip multiprocessor (CMP) system, for a given power budget, by developing techniques to budget power between processor cores and caches. Dynamic cache configuration can reduce cache capacity and associativity, thereby freeing up chip power, but may increase the miss rate (and potentially memory power). Dynamic voltage and frequency scaling (DVFS) can exploit the saved power to increase core performance, potentially increasing system performance. Detailed simulation models show that carefully budgeting power between cores and caches can improve system performance 2-16% for 11 of 17 workloads. To intelligently budget power between cores and caches, we investigate using hardware support to drive analytical models of system power and performance. Online estimation enables real-time feedback and adaptation to dynamic changes such as operating system interactions or changing workload mixes. We demonstrate an integrated online framework that combines a cache reuse model, performance model, power model and DVFS model to identify optimal power-budgeted configurations.