Interesting PEZY-SC4s

Summary

Japan has a long history of building domestic supercomputer architectures dating back to the 1980s. PEZY Computing is one player in Japan’s supercomputing scene alongside Fujitsu and NEC, and has taken several spots in the Green500 list. RIKEN’s Exascaler-1.4 used PEZY-SC chips to take first place in Green500’s November 2015 rankings. More recently, PEZY-SC3 placed 12th on Green500’s November 2021 list. PEZY presented their newest architecture, PEZY-SC4S, at Hot Chips 2025. While the physical product is not yet available, PEZY is presenting results of simulations and is talking about the architecture of SC4s.PEZY targets highly efficient FP64 compute by running a massively parallel array of execution units at lower clocks and voltages than contemporary GPUs. At the same time, it tries to avoid glass jaw performance behavior with low branching penalties and a sophisticated cache hierarchy. Their PEZY-SC products connect to a host system via PCIe, much like a GPU. The ‘s’ in SC4s denotes a scaled down model that uses a smaller die and draws less power. For example, PEZY-SC3 used a 786 mm2 die on TSMC’s 7nm process and drew up to 470W. PEZY-SC3s uses a smaller 109 mm2 die with a milder 80W power draw, and has 512 Processing Elements (PEs) compared to 4096 on the larger PEZY-SC3.PEZY-SC4s is large for a ‘s’ part, with the same per-clock throughput as SC3. A bump from 1.2 to 1.5 GHz gives it a slight lead in overall throughput compared to SC3, and places it well ahead of SC3s.From an organization perspective, a PEZY PE is somewhat analogous to an execution unit partition on a GPU, like AMD’s SIMD or Nvidia’s SM sub-partitions. They’re very small cores that hide latency using thread level parallelism. On PEZY-SC4s, a PE has eight hardware threads, a bit like SMT8 on a CPU. These eight threads are arranged in pairs of “front” and “back” threads, but it’s probably more intuitive to see this is two groups of four threads. One four-thread group is active at a time. Hardware c...