[R] No performance increase from dual-core processors?

Prof Brian Ripley ripley at stats.ox.ac.uk
Tue Dec 27 08:32:20 CET 2005

R only runs multiple computational threads as part of a BLAS/LAPACK addon 
on Unix-alikes, so no speed-up is expected from dual processors (which 
includes Intel's HyperThreading, as well as dual-cored systems).

A faster processor would give you considerable increases even single-core,
and a 2.8GHz Pentium is quite slow compared to an Athlon64 or Opteron
(as you have found: P4 systems are slow for their clock speeds compared to 
PIIIs (such as Pentium M) or almost anything else).  My 2GHz Pentium M 
laptop is faster than my 2.8GHz P4 home desktop, and an Opteron 252 is 
considerably faster again (even running a 64-bit OS and build of R).

BTW, testing 500,000 normals is a single R command and is for me fast 
enough to be hard to time accurately:

> system.time(x <- rnorm(5e5))
[1] 0.10 0.01 0.10 0.00 0.00

on an Opteron 252.

On Mon, 26 Dec 2005, Adam Petrie wrote:

> Hey all,
> I was planning on getting a new computer for the new year to help with
> my dissertation research, and recently had an opportunity to compare the
> performance of my 1.6 GHz Pentium M laptop, and a 2.8 GHz dual-core
> Pentium processor (both running WinXP professional 32-bit).  I run a lot
> of long simulations, so I was hoping to get something that would speed
> them up.  I ran a few quick computation tests (e.g.  generating 500,000
> normals), and found the performance increase of the 2.8 dual-core over
> my 1.6M laptop to be negligable (and in fact sometimes slower).  One
> thing I did notice that if I look at the CPU usage of my laptop when
> it's performing the simulations the laptop is at about 100%, while the
> dual-core reaches 50% (and seems to refuse to go higher than 50% no
> matter what).  Of course if I load up 2 instances of R I can get them to
> run the simulations simultaneously in about the same amount of time, but
> this doesn't help me get to the end of a very long simulation quicker.
> This got me thinking that no matter what kind of processor I get, I'm
> not going to be getting a large speed increase over what I already
> have.  Does anyone have any insight into various setups/processors that
> would help me speed up my work (e.g. maybe run R through linux, Pentium
> extreme edition, etc)?
> Thanks in advance,
> Adam Petrie
> Rensselaer Polytechnic Institute
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Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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