Towards sustainable exascale computing

High Performance Computing systems have shown an impressive growth so far with a performance increase of 10x every 3.6 years. Performance predictions seem to confirm this trend for the future: Roadrunner achieved 1 petaFLOPS in 2008 and 10 petaFLOPS system are expected to be operational in the next few years. If these predictions are correct, exascale performance will be achieved by 2018. Power consumption is increasing at a faster rate than performance, which is making HPC not sustainable with current technologies. A DARPA study states that exascale systems will be limited to a total power budget of 20-25 MW: in order to achieve 1 exaFLOPS, HPC systems have to provide 40 GLOPS/W, two orders of magnitude higher than the current fastest supercomputer. It seems clear that current technologies will not provide such efficiency and that there are new research challenges and opportunities on the way to the exascale era. This paper shows how a closer hardware/software interaction can improve HPC system's efficiency. New technologies will provide better power management but will also slow down applications. System software, on the other hand, can detect applications behavior and trigger the most effective hardware mechanisms without introducing excessive performance degradation.