Translations:OpenACC Tutorial - Adding directives/17/en

Those who have used OpenMP before will be familiar with the directive based nature of OpenACC. There is however one major difference between OpenMP and OpenACC directives:

• OpenMP directives are by design prescriptive in nature. This means that the compiler is required to perform the requested parallelization, no matter whether this is good from a performance stand point or not. This yields very reproducible results from one compiler to the next. This also means that parallelization will be performed the same way, whatever the hardware the code runs on. However, not every architecture performs best with code written the same way. Sometimes, it may be beneficial to switch the order of loops for example. If one were to parallelize a code with OpenMP and wanted it to perform optimally on multiple different architectures, they would have to write different sets of directives for different architectures.