On Thu, Nov 24, 2011 at 4:10 PM, Jed Brown <[email protected]> wrote:

On Thu, Nov 24, 2011 at 16:01, Barry Smith <[email protected]> wrote:

...

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.

What exactly should I be looking at? Can't you have all the threads spin on a normal shared variable (not a mutex) that is only written by the thread that needs to spark them? Or use a fetch-and-add atomic if you want to keep track of how many are running or limit the number? The latter could use a tree to get logarithmic cost, but if they are stored next to each other, you would still have O(P) cache invalidations.

This is one great reason that vectorization works and pthreads is crap. I am not totally sold on the thread block system, but it looks like genius compared to pthreads. I would start there. Matt -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener