Monday, June 22, 2020

Stop throwing GPU at HPC, Not all scientific problems are compute dense

The current race to exascale has put a heavy emphasis on GPU-based acceleration at the detriment of other HPC architecture. However, Crossroads and Fugaku supercomputer are demonstrating that it is not all about GPU.

The vast majority of the (pre-)exascale machines are relying heavily on GPU acceleration targeting scientific problems that can be cast as dense matrix-matrix multiplication problems.

However, there are large numbers of scientific problems that are not compute dense. And such GPU architectures are ill-equipped to accelerate these problems. Sadly, the current trends seem to have relegated those type of scientific challenges to second class citizens in the HPC world. If you look at extreme-scale graph problems by example, the graph500 benchmark clearly shows that these type of problem have been orphaned. 4 out of ten systems are more than seven years old and nearing their end of life. Moreover, the newer systems show marginal progress toward accelerating extreme-scale graph traversal. 

I understand that the current machine learning hype heavily influences the HPC ecosystem. However, we have to remind ourselves that there is life beyond FLOPS. And the Fugaku and Crossroads system demonstrates it is possible to achieve strategic compute leadership without sacrificing the architecture to the altar of exaflop compute dense gods. 

The Japanese latest ARM-based Fugaku supercomputer is demonstrating that it can address both compute dense GPU optimised and the one that not reducible to dense linear algebra and therefore incompatible with GPU technologies. The Japanese supercomputer built around the ARM v8.2A A64FX CPU just picked up the number one in the HPC Top 500 Green benchmark and the Graph500 BFS benchmark.

Hopefully, this will be a wake-up call within the HPC community to properly fund R&D efforts orthogonal to the compute dense and exaflops benchmark friendly architecture.

Update 22/06/2020 : after publishing this article Fugaku just got ranked Nb 1 at the top 500 Linpack benchmarks with close to half an exaflops! (415 Petaflops).And Fugaku is pretty much topping every single HPC ranking :

  • Top500 : Nb 1.
  • Top500-Green : Nb 1.
  • HPCG : Nb 1.
  • HPL-AI: Nb 1.
  • Graph500 : Nb 1.

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