Le Tue, 8 Nov 2011 16:25:22 -0800, Nat Echols <nathaniel.ech...@gmail.com> a écrit :
> On Tue, Nov 8, 2011 at 4:22 PM, Francois Berenger <beren...@riken.jp> > wrote: > > In the past I have been quite badly surprised by > > the no-acceleration I gained when using OpenMP > > with some of my programs... :( You need big parallel jobs and avoid synchronisations, barriers or this kind of things. Using data reduction is much more efficient. It's working very well for structure factors calculations for exemple. > > Amdahl's law is cruel: > > http://en.wikipedia.org/wiki/Amdahl's_law You can have much less than 5% of serial code. I have more problems with L2 misse cache events and memory bandwidth. A quad cores means 4 times the bandwidth necessary for a single process... If your code is already a bit greedy, the scale up is not good. Pascal
