On 8/11/07, Hugh Perkins
- parallelism must be quite coarse to offset overheads (which I think is the problem with expecting things like map and fold to parallelised automagically; they're just too small grained for it to be worthwhile)
Someone else said that. I dont understand what you mean.
There are many papers about this in the Parallel Logic Programming area. It is commonly called "Embarrassing Parallelism". Creating a thread, or even just scheduling a chunk of work for evaluation has packaging-up costs, synchronization costs, and so on. It is all too easy for these costs to outweigh the work to be done, so by parallelizing your code, you make it run slower. So, if you want to parallelize "map f xs", unless f is *really* expensive, you'll only get a benefit if you can break xs into chunks of e.g. 10^3 elements or more, and more like 10^5 or more for more usual 'f's. Some tasks, like Monte Carlo integration are very amenable to such, but most tasks are not. cheers, T. -- Dr Thomas Conway drtomc@gmail.com Silence is the perfectest herald of joy: I were but little happy, if I could say how much.