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

[Douglas Bates]

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.