[R-SIG-Mac] FAQ? Mac distributed/multiple processor solutions?

[Prof Brian Ripley]

On Thu, 6 Dec 2007, Ken Beath wrote:

> On 05/12/2007, at 5:57 AM, Thomas Lumley wrote:
>
>> On Tue, 4 Dec 2007, Rob Forsyth wrote:
>>> options here. I am working on an iMac G5 and could access (at home -
>>> i.e. not on a LAN) another G5 and a G4. I've come across the R/MPI
>>> package but would appreciate advice as to how easy this is to set up
>>> (would it actually be simpler to divide the job "manually"?).
>>
>> With only three computers it would be easiest to divide the job
>> manually.
>>
>
> Much easier, and if you have access to a machine with multiple
> processors, simply duplicate the R process to have the same number as
> the number of processors, and then run them simultaneously. Not as
> elegant and maybe not as efficient as other methods, but effective.

But those processes need to do different things (and record the results in 
different files), which is what Thomas means by 'divide the job manually'.

Incidentally, I find it useful to run slightly more R processes than the 
number of processors, to ensure full CPU usage when one of the processes 
is in an I/O wait or hits a swapping trap.  (Provided you have ample RAM 
or you will get additional swapping.)

Even with many processors it may be easisest to do this manually.  Our 
geneticists do simulation-based inference by running separate simulation 
runs on up to 100s of processors simultaneously: the scheduler works 
better with independent jobs.

-- 
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