From matloff at cs.ucdavis.edu  Sun Dec 16 01:38:50 2012
From: matloff at cs.ucdavis.edu (Norm Matloff)
Date: Sat, 15 Dec 2012 16:38:50 -0800
Subject: [Rd] SUGGESTION: Add get/setCores() to 'parallel' (and command
 line option --max-cores)
Message-ID: <20121216003850.GB9435@laura>

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.

Norm



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