I'm using a dual hex core machine. It has 12 real processors but shows as 24 on Linux due to hyperthreading. I'm using 10 workers so I can have them to myself while other people use the others for small stuff. I do see them go to 100% sometimes, just not during most of my loop going in and out of spmd.
By the way, is it possible to plot while still in the spmd? I like to put up a plot as I go to monitor progress.
Edric M Ellis <email@example.com> wrote in message <firstname.lastname@example.org>...
> > What size MATLABPOOL did you open? One thing to note: MATLAB doesn't > consider hyperthreaded cores when choosing how many processes to make > the default for the local scheduler - so even if all the workers were > completely busy, you might not see more than 50% utilisation. (That's > what happens here on my system - the OS thinks it has 12 cores, but > really it has 6 hyperthreaded cores, so the default is for MATLAB to > launch 6 local workers). > > > Any alternatives? For one, is there a way to gather directly worker > > to worker without exiting spmd and bringing it all to the master? > > You can use functions like either labBroadcast to send data from one > worker to all the others, and gcat or gop to perform 'reduction' > operations. Very briefly, here's how they work > > % assume matlabpool size 4 > spmd > data = rand(); > > % broadcast from lab 1, x1 gets the value from 'data' on lab 1. > x1 = labBroadcast(1, data); > > % concatenation - each lab gets x2 = [1 2 3 4]; > x2 = gcat(labindex); > > % general reduction - in this case, each lab gets > % x3 = 1 + 2 + 3 + 4 > x3 = gop(@plus, labindex); > end > > > The data is small and functions cheap, so maybe I'd be ahead to let > > everyone do the same computations just to keep things flowing. > > That sounds like a very good idea. > > Cheers, > > Edric.