Re: [R] Which Linux OS on Athlon amd64, to comfortably run R?

From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>
Date: Thu, 6 Dec 2007 07:07:09 +0000 (GMT)

On Thu, 6 Dec 2007, Emmanuel Charpentier wrote:

> Prof Brian Ripley a écrit :
>> Note that Ottorino has only 1GB of RAM installed, which makes a 64-bit
>> version of R somewhat moot. See chapter 8 of
>>
>> http://cran.r-project.org/doc/manuals/R-admin.html
>
> Thank you for this reminder|tip ! I didn't re-read this document since
> ... oh, my ... very early (1.x ?) versions. At which time my favorite
> peeve against R was the fixed memory allocation scheme.
>
> I would have thought that 64 bits machines could take advantage of a
> wider bus and (marginally ?) faster instructions to balance larger
> pointers. Am I mistaken ?

Yes, it is more complex than that. If you run 32-bit instructions on a x86_64, the physical bus is the same as when you run 64-bit instructions. The larger code usually means the CPU caches spill more often, and some 64-bit chips have more 32-bit than 64-bit registers which allows better scheduling.

The R-admin manual reports on some empirical testing. But when you have limited RAM the larger code and data for a 64-bit build will cause more swapping and that is likely to dominate performance issues on large problems.

Note that the comparisons depend on both the chip and the OS: it seems that on Mac OS 10.5 on a Core 2 Duo the 64-bit version is faster (on small examples). The original enquiry was about 'amd64 linux', but I've checked Intel Core 2 Duo as well: on my box 64-bit builds are faster than 32-bit ones, whereas the reverse is true for Opterons. So it seems that the architectural differences of Core 2 Duo vs AMD64 do affect the issue.

-- 
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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Received on Thu 06 Dec 2007 - 07:11:19 GMT

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