The new Green500 list, the one that ranks Top500 supercomps by their FLOPS/Watt efficiency is out, and the new #1 is again an IBM BG/Q prototype. The machine, scoring at 2,097 MFLOPS/W is about 25% more efficient than the previous BG/Q prototype, which scored 1,684 MFLOPS/W. The BG/Q design is based on low-power PowerPC A2 chips, each one containing 16 cores. Unfortunately I am unable to find more information that would explain why this new prototype is more than 2x more efficient than production GPU supercomps such as GSIC's Tsubame 2.0 (958.35 MFLOPS/W), or, even more intriguing: what did they change in between the two prototypes that boosted the efficiency in 25%?
Interestingly, Nagasaki University scored #3 deploying a GPU cluster that achieves 1375.88 MFLOPS/W. This system is based on ATI/AMD cards. Nvidia GPUs have a much higher presence in HPC, but when it comes to Green500 the gap is much closer, with two AMD systems and 3 NVIDIA systems in the top 10.
Also interesting is the fact that the top supercomputer in the Top500 list (The Fujitsu-based K Computer) is #6 in the Green500 list at a respectable 824.56 MFLOPS/W. This demonstrates the efficiency of the Fujitsu SPARC64 VIIIfx chips and the Tofu interconnect.
More information: Top500 and Green500
