Multiprocessor research at Åbo Akademi Ralph-Johan Back

Early 80’s Work on distributed systems –joint work with Reino Kurki-Suonio –formalizing, constructing, analyzing, verifying distributed systems –point-to-point networks, wlans, etc –courses on distributed systems at ÅA –research on language CSP (C.A.R. Hoare) –very theoretical work, needed some practical case studies to look at

Mid 80’s Inmos starts designing the transputer –Special processor that has four links for communication with neighbours –Specially designed for building parallel processors T800

Hathi-project VTT Oulu contacted us, wanted to build a parallel computer –Tapani Äijänen, Kari Leppänen from VTT TEKES project (Hathi, ): –VTT built hardware –ÅA built software First version: Hathi-1, 16 processors –Mats Aspnäs project manager from ÅA Used for experimentation Lots of case studies in building parallel systems

Finsoft III program TEKES starts a new large research program (Finsoft, in three parts, ) –I was director of Finsoft III- parallel processing and neural networks –12 different research projects in Finsoft III, 7 in parallel processing and 5 in neural networks –ÅA had 2 large projects: Millipede and Centipede Millipede: Massively parallel processors Centipede: Construction and correctness of Parallel Systems –Quite a large number of people enganged in Millipede U. Solin, Hong Shen got Ph.D. from this many M.Sc. thesis.

Millipede Built Hathi-2 in Millipede –VTT/Oulu built hardware –ÅA built software Largest supercomputer in Finland at that time –Connected to the university network (internet) –A reasonable number of research groups were using Hathi-2, in different universities –Different kinds of applications, mainly CS and scientific computing Many Ph.D. and M.Sc thesis around Hathi-1 and Hahi-2.

Hathi-2 Hathi-2 construction –100 Transputer 800 floating point processors –Connected in a mesh structure –Dynamically reconfigurable connection structure –25 smaller Transputers connected in a ring, to monitor and control the floating point processors Physically –size of a larger refrigator, –with 25 boards, –each board containing 4 T800 and 1 smaller transputer

Hathi-2 Hathi-2 system software –Reconfiguring the conection structure –Mapping logical processor structure onto physical structure –Monitoring software for performance measurements Hathi-2 application software –Nuclear physics –Solving differential equations –CFD (Computational fluid dynamics) –Cosmology –Full text retrieval –....

Main challenges Writing software as collection of parallel processes was difficult –Occam language from Inmos based on CSP –orchestrating communication by means of message passing –problems with deadlocks and livelocks Lots of algorithmic problems –laying out a logical process net on a physical processor network required strong heuristics –Monitoring computation without interfering required careful embedded system design –Partitioning software to allow for parallel computation In the end, writing software for massively parallel processors was not that much more difficult that writing ordinary software

Early 90’ I went for a sabbatical to Caltech ( ) –Center for massively parallel computer research –Chuck Seiz built first cosmic cube –Chuck was working on really large processor array (16K processors) However –I worked mostly on formal methods in programming –And participated in Alain Martins group on the design of asynchronous VLSI circuits –Was not that intrested in multiprocessor hardware design

T9000 transputer We planned to build Hathi-3 –T800 processors had become too slow compared to the competitors We needed the new T9000 transputers –very efficient –had wormhole routing, so arbitrary dynamic routing at run time –competed with best Intel and Motorola processors at that time Inmos had difficulties in building T9000 in quantity –quality of produced processors was not good enough –Inmos was bought up by other companies –in the end, they stopped the development of a new transputer generation

End of Hathi Did not want to continue working with other processors – Intel or Motorola processors were much inferior to Inmos transputers for parallel systems –Could not build own transputer Hathi-3 was never built Hathi-2 was deplugged in