[Rcpp-devel] RcppArmadillo BLAS/LAPACK force number of threads to 1

[Yixuan Qiu]

Good point by Dirk.

And why not just adding a line "export OPENBLAS_NUM_THREADS=1" to your
.bashrc file, or compiling OpenBlas again by setting NUM_THREADS = 1 in the
Makefile.rule?


Best,
Yixuan


2014-08-11 18:55 GMT-04:00 Dirk Eddelbuettel <edd at debian.org>:

>
> Hi Scott,
>
>
> On 12 August 2014 at 08:43, Scott Ritchie wrote:
> | Hi Everyone,
> |
> | I'm having trouble with restricting the Armadillo function "svd_econ" to
> run on
> | a single thread.
> |
> | I am able to restrict it if I `export OPENBLAS_NUM_THREADS=1` before
> opening an
> | R session, but not from within R (`Sys.setenv(OPENBLAS_NUM_THREADS=1)`
> has no
> | effect).
> |
> | I'm wondering if theirs an option native to armadillo/RcppArmadillo that
> I'm
> | missing to enable me to:
> |
> |   • Restrict the number of threads used to 1
> |   • In a library agnostic manner (i.e. if the user has a different
> LAPACK or
> |     BLAS library installed).
> |
> | or if I can "trick" Rcpp into thinking the machine only has 1 core?
>
> I fear you may be misstating / misdiagnosing the problem.
>
> I am fairly certain that there is not a single line in Rcpp or
> (Rcpp)Armadillo which sets thread counts for your LAPACK / BLAS.
>
> Rather, and this is a point that I tried to make in the 'Benchmarking GPUs
> and CPUs on Debian-based systems' package (gcbd on CRAN etc) and its
> vignette
> is that __BLAS and LAPACK sit behind a standardized interface__ and can be
> installed / swapped via plug and play. (Which in turn enables the
> benchmarking ...)
>
> If you're on a Debian-based system, just remove openblas and use atlas.
> Case
> closed.  Atlas will not multithread (unless something changed recently).
>
> There is also a helper function or package somewhere, and a post by Claudia
> Beleites on StackOverflow, which show the explicit function call to reset
> OpenBLAS in its count.  But if everything else fails -- just use a
> different
> BLAS.  I sometimes do that too when I use multicore / parallel to launch
> multiple R jobs and each one of those should not spawn additional linear
> algebra threads.
>
> Hope this helps,  Dirk
>
>
>
> | Regards,
> |
> | Scott Ritchie
> | _______________________________________________
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>
> --
> http://dirk.eddelbuettel.com | @eddelbuettel | edd at debian.org
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-- 
Yixuan Qiu <yixuan.qiu at cos.name>
Department of Statistics,
Purdue University
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