[R] CPU or memory

[Prof Brian Ripley]

On Wed, 8 Nov 2006, Stefan Grosse wrote:

> 64bit does not make anything faster. It is only of use if you want to
> use more then 4 GB of RAM of if you need a higher precision of your
> variables
>
> The dual core question: dual core is faster if programs are able to use
> that. What is sure that R cannot make (until now) use of the two cores
> if you are stuck on Windows. It works excellent if you use Linux. So if
> you want dual core you should work with linux (and then its faster of
> course).

Not necessarily.  We have seen several examples in which using a 
multithreaded BLAS (the only easy way to make use of multiple CPUs under 
Linux for a single R process) makes things many times slower.  For tasks 
that are do not make heavy use of linear algebra, the advantage of a 
multithreaded BLAS is small, and even from those which do the speed-up is 
rarely close to double for a dual-CPU system.

John mentioned simulations.  Often by far the most effective way to use a 
multi-CPU platform (and I have had one as my desktop for over a decade) is 
to use coarse-grained parallelism: run two or more processes each doing 
some of the simulation runs.

> The Core 2 duo is the fastest processor at the moment however.
>
> (the E6600 has a good price/performance ration)
>
> What I already told Taka is that it is probably always a good idea to
> improve your code for which purpose you could ask in this mailing
> list... (And I am very sure that you have there a lot of potential).
> Another speeding up possibility is e.g. using the atlas library...
> (where I am not sure if you already use it)
>
> Stefan
>
> John C Frain schrieb:
>> *Can I extend Taka's question?*
>> **
>> *Many of my programs in (mainly simulations in R which are cpu bound) on a
>> year old PC ( Intel(R) Pentium(R) M processor 1.73GHz or Dell GX380
>> with 2.8Gh Pentium) are taking hours and perhaps days to complete on a
>> one year old
>> PC.  I am looking at an upgrade but the variety of cpu's available is
>> confusing at least.   Does any one know of comparisons of the Pentium
>> 9x0, Pentium(r)
>> Extreme/Core 2 Duo,   AMD(r) Athlon(r) 64 , AMD(r) Athlon(r) 64
>> FX/Dual Core AM2 and
>> similar chips when used for this kind of work.  Does anyone have any advice
>> on (1)  the use of a single core or dual core cpu or (2) on the use of 32
>> bit and 64 bit cpu.  This question is now much more difficult as the numbers
>> on the various chips do not necessarily refer to the relative speed of the
>> chips.
>> *
>> *John
>>
>> * On 06/11/06, Taka Matzmoto <sell_mirage_ne at hotmail.com> wrote:
>>
>>
>>> Hi R users
>>>
>>> Having both a faster CPU and more memory will boost computing power. I was
>>> wondering if only adding more memory (1GB -> 2GB)  will significantly
>>> reduce
>>> R computation time?
>>>
>>> Taka,
>>>
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>>
>>
>>
>>
>
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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