A Sunday 20 February 2011 00:01:59 Sturla Molden escrigué: > pthreads will give you better control than OpenMP, but are messy and > painful to work with. > > With MPI you have separate processes, so everything is completely > isolated. It's more difficult to program and debug than OpenMP code, > but will usually perform better.
To be more specific, MPI will perform better if you don't need to share the memory of your working set among all your processes, but in case you need to do this, threads (pthreads, OpenMP) lets you access all parts of the working set in memory much more easily. In fact, all the threads of a process can access the complete working set transparently and efficiently (although this is precisely why they are trickier to program: you have to explicitly avoid simultaneous writing in the same memory area), not to mention that threads are much cheaper to create than processes. Generally speaking, if your problem is large, CPU intensive and not very memory bounded, MPI usually leads to better results. Otherwise threads tend to do a better job. The thing is that memory is increasingly becoming more and more a bottleneck nowadays, so threads are here to stay for a long, long time (which is certainly unfortunate for programmers, specially for pthreads ones :). -- Francesc Alted _______________________________________________ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
