[R] (performance) time in Windows vs Linux

[Raymond Wan]

Hi Brian,

Thank you for the clarification -- the first part does set the record 
straight about what I thought about R.  I would expect a program to run 
on a single core by default unless something specifically (and somewhat 
non-trivial) was done to it.


Prof Brian Ripley wrote:
>> If you want to check if R is running on more than one core, then 
>> obviously R should appear more than once and with two different values 
>> under CPU.
> 
> Not so: that will happen if multiple copies of R are running, not if a 
> single copy of R is running multiple threads.


Ah, yes, you are right -- there is a big difference.  The former works 
for both multiple copies of R or a single program [purposely not saying 
"R" here to keep it general] running on multiple cores [distributed 
memory parallelization].  It doesn't work for multiple threads, though.

(As an aside for anyone else interested, my Debian distribution has the 
package "r-cran-rmpi", which is described as the "GNU R package 
interfacing MPI libraries"...so that seems to be another way to use 
multiple cores, though I have never used it...)

Ray