Code_Saturne has recently obtained a “gold award” in parallel computing on United Kingdom’s HPCxsupercomputer, located at Daresbury Laboratory. This very satisfying result is a reward for the work undertaken for some years nowby the Code_Saturne development team on the optimisation of the code and its adaptation to High Performance Computing.
HPCx supercomputer at Daresbury Laboratory (UK) (photo credits Daresbury Laboratory, used with permission)
Unlike the vector supercomputers of lastdecade, today’s machines are generally composed of quite simple processors, but in large number (sometimes up to hundreds of thousands). During a computation, the considered domain is divided in as many sub-volumes as the number of processors used. Hence, each processor only deals with a fraction of the domain, on which computations are much faster. But on the other hand, these sub-volumes need to communicate with one another. When increasing the number of processors used for a computation, the time used for proper calculation decreases, but the communication phase takes longer. Eventually, the time spent in communications will become predominant and counteract the effect of the increase in the number of processors. The “scalability” of a software measures its behavior with respect to an increase in the number of processors used for a calculation. The more optimised its communication phases are, the more efficient the code will remain on a large number of processors. The current test was carried out by Daresbury Laboratory on the HPCx machine, in collaboration with the University of Manchester. It consists in analysing the performances of Code_Saturne when multiplying the number of processors by two. To obtain a “gold award”, the code must be at least 1.7 times faster on 1024 processors than on 512 (in case of optimal scalability, with no efficiency loss due to communications, the code would ideally run twice as fast). The result obtained by Code_Saturne is 1.84, well above the required limit.
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DaresburyLaboratory is a member of the Science and Technology Facilities Council, in charge of world-class, large scale research facilities in the UK (high performance computing, synchrotrons, lasers, ...).