I am running R 2.4.1 on the new 8-core Mac Pro with the parSapply
function from the Snow package. Tests using 2,4, and 8 threads with
makeCluster() yield somewhat disappointing results. The 4 thread process
is fastest. With 8 threads, all the cores max out at about 70% power,
and even then it is slower than the 4 thread process which maxes out the
4 threads at about 90-95%. This suggests the additional 4 cores on the
Mac Pro do not improve performance in an embarrassingly parallel R/Snow
environment...
The function I tested in parSapply runs a regression (a call to "lm"). I
am using Snow/rpvm package combination. There is no issue of limited
memory. There are over 3 gigs of free RAM in the tests.