[R] re: smp in Linux

[Thomas Lumley]

On Wed, 10 Mar 1999, Kenneth Nordstrom wrote:
 
> A question to all you R-gurus:
> 
> Can R (or S-plus, for that matter) make efficient use
> of multiple Intel Processors running under Linux (within 
> the same PC, not over a net)? 
> With the release of the new 2.2 kernel, this would seem 
> a interesting and cost-efficient way of boosting the 
> computational power of Intel/Linux platforms when using 
> R (or S-plus).

R is not currently multithreaded or otherwise parallelised. Threading is
in the list of things that would be interesting to do sometime in the
distant future. It will be hard.

There are possibilities for parallelisation short of making R fully
threaded.  One more-or-less straightforward one would be to replace the
matrix operations with efficient parallel code. This wouldn't help a lot
since R doesn't spend that much time doing matrix operations.  Another
possibility would be to run the graphics drivers in parallel with the main
code. This wouldn't help much, either, unless you routinely draw
high-resolution images or overloaded scatterplots.

A third possibility, which would be more difficult but might actually gain
something is to thread the "findVarInFrame" search. I did some profiling
last year sometime and this was taking up 20% of the execution time on
the examples I looked at. Cutting this in half might actually be 
noticeable.

On the other hand, most of the problems I have where speed is an issue are
simulations or bootstrapping problems that scale almost perfectly by
running 1/n as many on each of n processors.  I have managed 190% CPU
utilisation by two copies of R on a dual Pentium Pro even under an older
Linux kernel.


Thomas Lumley
Assistant Professor, Biostatistics
University of Washington, Seattle

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