[Rd] SUGGESTION: Add get/setCores() to 'parallel' (and command line option --max-cores)

Norm Matloff matloff at cs.ucdavis.edu
Sun Dec 16 01:38:50 CET 2012

Henrik Bengtsson <hb at biostat.ucsf.edu> wrote:

^ In the 'parallel' package there is detectCores(), which tries its best
^ to infer the number of cores on the current machine.  This is useful
^ if you wish to utilize the *maximum* number of cores on the machine.
^ Several are using this to set the number of cores when parallelizing,
^ sometimes also hardcoded within 3rd-party scripts/package code, but
^ there are several settings where you wish to use fewer, e.g. in a
^ compute cluster where you R session is given only a portion of the
^ cores available.  Because of this, I'd like to propose to add
^ getCores(), which by default returns what detectCores() gives, but can

Even if one has the entire machine to oneself, there is often another
very good reason not to use the maximum number of cores:  Using the
maximum number of cores may reduce performance.  This is true in
general, and sometimes especially true when the inferred number of cores
includes hyperthreading.


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