On Nov 24, 2011, at 3:56 PM, Jed Brown wrote: > On Thu, Nov 24, 2011 at 15:44, Barry Smith <bsmith at mcs.anl.gov> wrote: > I totally agree with you on this. Where we disagree is thatI don't believe > that MPI or pthreads have what is needed. For example since pthreads > sequentializes the waking up threads it cannot be used in a way scalable to > hundreds of threads. > > Can't the threads all be live and poll on a shared variable?
Yes, but they can only get access to that shared variable one at a time: first get's it, then second get's it, then third gets, .... Ok for a couple of cores but not for dozens. Take a look at src/sys/objects/pthread.c for the various ways we have coded for "waking" the threads. Maybe I am missing something but this is the best Kerry and I could figure out. Barry > Or do you need a kernel-level primitive to activate a bunch of threads in one > call? (I think this depends whether you want to have more threads than > cores.) In any case, wouldn't that just be pthreads+1?
