On Fri, Jan 16, 2009 at 6:30 PM, Matthieu Brucher <matthieu.bruc...@gmail.com> wrote: > 2009/1/16 James Mills <prolo...@shortcircuit.net.au>: >> I've noticed over the past few weeks lots of questions >> asked about multi-processing (including myself). > > Funny, I was going to blog about this, but not just for Python. > >> For those of you new to multi-processing, perhaps this >> thread may help you. Some things I want to start off >> with to point out are: >> >> "multiprocessing will not always help you get things done faster." > > Of course. There are some programs that are I/O or memory bandwidth > bound. So if one of those bottlenecks is common to the cores you use, > you can't benefit from their use. > >> "be aware of I/O bound applications vs. CPU bound" > > Exactly. We read a lot about fold...@home, s...@home, they can be > distributed, as it is more or less "take a chunk, process it somewhere > and when you're finish tell me if there something interesting in it". > Not a lot of communications between the nodes. Then, there are other > applications that process a lot of data, they must read data from > memory, make one computation, read other data, compute a little bit > (finite difference schemes), and here we are memory bandwidth bound, > not CPU bound. > >> "multiple CPUs (cores) can compute multiple concurrent expressions - >> not read 2 files concurrently" > > Let's say that this is true for the usual computers. Clusters can make > concurrent reads, as long as there is the correct architecture behind. > Of course, if you only have one hard disk, you are limited. > >> "in some cases, you may be after distributed processing rather than >> multi or parallel processing" > > Of course. Clusters can be expensive, their interconnections even > more. So if your application is made of independent blocks that can > run on small nodes, without much I/Os, you can try distributed > computing. If you need big nodes with high-speed interconnections, you > will have to use parallel processing. > > This is just what my thoughts on the sucjet are, but I think I'm not > far from the truth. Of course, if I'm proved wrong, I'll be glad to > hear why.
Thank you Matthieu for your response. Very good comments on some of the points I raised. Hopefully those interested in the topic will learn from this thread. cheers James PS: I assumed you meant to post back to the list and not just me :) -- http://mail.python.org/mailman/listinfo/python-list
