Reducing the power consumption of applications has become is one of the key challenges in high performance computing. Recent processor architectures differentiate the processor core frequency (that affects the computation units and the L1 and L2 caches) from its uncore frequency (that affects the last level cache and the memory controller). As a consequence, in addition to tuning processor core frequency with DVFS, power consumption can also be controlled through Uncore Frequency Scaling (UFS). In this paper, we study how the uncore frequency impacts parallel applications performance and power consumption. We also propose DUF, a runtime system that dynamically adapts the uncore frequency in order to reduce an application power consumption with a user-defined limit on performance degradation. We evaluate DUF on 3 different architectures. The evaluation shows that when allowing a 10 % performance degradation, DUF can reduce the power consumption of applications by up to 21 %. We also show that DUF can reduce the total energy consumption of by up to 16.56%.