HIGH PERFORMANCE COMPUTING
“We do not have the capability to develop a chip that has this level of reliability, but Fujitsu has been doing that for years”
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Moonshot drives technology development While the development of exascale technologies are clearly much more challenging than standard HPC development, Matsuoka notes that the goals can be achieved through carefully planned partnerships. ‘Commercial technologies have skills
that we do not have. We cannot do detailed chip design. Fujitsu has been doing that for 50 to 60 years, if you count the mainframe days, so they have a wealth of experience, and the engineers and systems. Those are their assets, they are one of the few remaining companies left that can design server grade general- purpose CPUs. ‘It was a great collaboration with Riken and other universities spearheading innovations, and these elements being realised as a tangible product. Unless you have a chip that is ultra-reliable then the machine will crash every second. If you leave it academia to make a chip it would be very likely that this would happen,’ said Matsuoka. ‘We do not have the capability to
develop a chip that has this level of reliability but Fujitsu has been doing that for years. It was a fantastic combination of skillsets that allowed this moonshot-like development to come to fruition,’ added Matsuoka. The Riken centre has previously
focused on the use of Sparc-based silicon for its previous supercomputers. The K computer, for example, the predecessor to the Fugaku supercomputer at Riken today, was based on Sparc processor technology developed at Fujitsu. While it may seem that switching from one architecture to another, which uses completely different Industry Standard Architecture (ISA), would suggest that much of the work would be replacing the old technology with new, there is significant technology transfer from the K computer to Fugaku. ‘If you look at the processor
architecture, what the processor has to do on a very basic level is to understand
6 Scientific Computing World Autumn 2020
the instruction set. Instruction set architectures are like languages. You can convey the same meaning but there are different languages that you may choose to use,’ said Matsuoka. ‘However, if a language is only spoken by a thousand people, then you do not have the knowledge and resources that would be available in a more common language.’ ‘While Sparc, at one time, was very mainstream, in the heydays of Risk – maybe 20 to 30 years ago – the importance of Sparc diminished over time, and it has been replaced with X86 and other technologies,’ noted Matsuoka. ‘Fujitsu stuck with Sparc because they had considerable assets in Sparc-based codes.’
When planning the initial stages of
Fugaku around ten years ago, Riken and its partners were looking to adopt a new ISA for the next generation of supercomputers. ‘It would be a big risk and cost for Fujitsu
to switch to another ISA, but, on the other hand, if they stuck to Sparc they would be diminished into obscurity,’ stressed Matsuoka. ‘For HPC it is critically important that we
achieve generality, because we have gone mainstream.’ Matsuoka also noted that the ISA could
have been x86 but ‘there are some issues with x86 both at the system level and also from a licencing point of view, which made it almost impossible’. He continued: ‘Arm was the obvious
choice because it had already become a standard in the embedded space. In the
end, it was decided that we would use Arm and the rest is history,’
The legacy of the K computer With this large change in technology and all the development that went into the new system and its associated technologies, what lessons or knowledge has been taken forward and helped the development of this new system? From the perspective of professor Matsuoka, there has been a significant transfer of technology which benefits scientists, and also makes it easier for technology development in the future. Matsuoka states: ‘Then the question is,
is there any legacy of K embedded into the machine or the architecture? The answer from the ISA perspective is, of course, no, because it is a completely different language, so to speak, but there are many other remnants that exist. ‘The most pronounced is the fact that
when Fujitsu designs its chips they divide it into the front and backend. The back end is fairly oblivious to the instruction set, because every language basically does the same thing. The backend of Fujitsu has been inherited over many years. It has been used for K, of course with evolutions, with gradual evolutions to add features but basically, it is the same backend. ‘For Fugaku, the backend is an evolution of the design but there are commonalities with K’s backend. It is not a direct re- utilisation, execution is much wider. There are memory enhancements and many other enhancements, but the baseline architecture is the same,’ he said.
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