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high-performance computing

industry to have a widely used standard approach to programming accelerated systems, so it is hoped that the major participants continue to drive towards this goal as fast as is reasonably possible. OpenMP and OpenACC offer an

evolutionary strategy for moving serial codes to parallel systems, and parallel codes to accelerated systems. Once the hot spots in a code have been identified, adding pragmas in that area can help the compiler to optimise these time-consuming sections of code. Although this strategy won’t always give the best performance without additional tuning, it does mean there is a very low barrier for entry into the world of accelerated computing. Te accelerated computing market is

evolving rapidly, while standardisation is generally delayed until a market is more stable. A standard way of building applications that use accelerators (most likely with OpenMP) would provide a benefit to users, in that they would only have to port a code once and could then target whatever accelerator was the flavour of the day. Having said that, tuning would be required to get the very best out of each target architecture – but at least an application would be portable between accelerated


architectures. Progress is being made (the latest OpenMP standard – OpenMP 4.0 – includes support for accelerators that is similar to that offered in the initial version of OpenACC), but faster progress would help the market for accelerators grow, and make life easier for users. Tis year, 2014, will see a number of

important compiler vendors producing OpenMP 4.0-compliant compilers (which includes the first cut at accelerator directives). While the underlying philosophy of what is offered by OpenMP for accelerators is the same as that provided by OpenACC, there are differences in implementation that may make it difficult to reconcile the latest version of OpenACC (which relies on greater compiler automation) with an easy evolution of OpenMP. Perhaps the battle between OpenMP and OpenACC will be fought, not l @scwmagazine FEBRUARY/MARCH 2014 19


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