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As clock frequency and die area increase, achieving energy efficiency, while distributing a low skew, global clock signal becomes increasingly difficult. Challenges imposed by deep-submicron technologies can be alleviated by using a multiple voltage/multiple frequency island design style, otherwise called the globally asynchronous, locally synchronous (GALS) design paradigm. This paper proposes a clustered architecture that enables application-adaptive energy efficiency through the use of dynamic voltage scaling for application code that is rendered non-critical for the overall performance, at run-time. As opposed to task scheduling using dynamic voltage scaling (DVS) that exploits workload variations across applications, our approach targets workload variations within the same application, while on-the fly classifying code as critical or noncritical and adapting to changes in the criticality of such code portions. Our results show that application adaptive variable voltage/variable frequency clustered architectures are up to 22% better in energy and 11% better in energy-delay product than their non-adaptive counterparts, while providing up to 31% more energy savings when compared to DVS applied globally.