One major advantage of reconfigurable computing systems is their ability to reconfigure hardware at runtime. In this paper, we study the feasibility of achieving energy efficiency in reconfigurable computing systems (e.g., FPGAs) through runtime partial reconfiguration (PR) techniques. In the ideal scenario, we use a hardware accelerator to accelerate certain parts of the program execution; when the accelerator is not active, we use partial reconfiguration to unload it to reduce power consumption. Since the reconfiguration process may introduce a high energy overhead, it is unclear whether this approach is efficient. To approach this problem, we first analytically identify the conditions under which partial reconfiguration can reduce energy consumption. Our results indicate that the key to reduce partial reconfiguration energy overhead is to minimize the time overhead of the reconfiguration process. Based on this analysis, we design and implement a fast reconfiguration engine that achieves close-to-ideal throughput on Xilinx Virtex-4 FPGAs. Our fast reconfiguration engine utilizes a master-slave DMA pair to stream data between the SRAM and the Internal Configuration Access Port (ICAP). We experimentally verify our proposed solutions and compare our design to existing energy reduction techniques, such as clock gating. The results of our study show that by using partial reconfiguration to eliminate the power consumption of the accelerator when it is inactive, we can accelerate program execution and at the same time reduce the overall energy consumption by half.

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