[R-sig-Debian] parallel BLAS for Ubuntu 11.10

[Dirk Eddelbuettel]

On 11 November 2011 at 11:45, Douglas Bates wrote:
| Added back the cc: to the R-SIG-Debian list
| 
| On Fri, Nov 11, 2011 at 11:13 AM, Paul Johnson <pauljohn32 at gmail.com> wrote:
| > Speaking of GotoBLAS, have you run into the problem of thread
| > management conflicts with RMPI?  In order to use GotoBLAS, the
| > submission script on our cluster has to explicitly restrict GotoBLAS's
| > effort to claim threads or else the jobs slow to a crawl as threads
| > multiply out of control.  It got to be enough of a hassle that I
| > stepped back from the whole Goto experience.
| >
| > Is it not a trouble now?
| 
| OpenBLAS will try to grab as many threads as there are cores available
| if you do not specify otherwise.  This is rather impolite behavior but
| comes from people wanting to squeeze out every possible cycle that
| they can.
| 
| One nice thing about the libopenblas-base package when recompiled
| locally is that there are several different environment variables that
| can be used to control the number of threads that it uses.  You can
| always set the environment variable
| 
| OMP_NUM_THREADS=2
| 
| but that will apply to all code using openmp.  If you set
| 
| OPENBLAS_NUM_THREADS=2
| 
| you can separately control other code using openmp.  The parallel
| package in R-2.14.0 and later uses similar controls.

... because it also uses the OpenMP constructs provided by gcc:

That said, I just grep'ed madly in the sources of parallel (as per R 2.14.0)
and didn't see it, nor did I see it in the vignette. I could swear I read it
in an earlier pre-release version of the parallel vignette. Hmm.

Dirk

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