On 23 February 2024 at 09:35, Robin Liu wrote: | Hi all, | | Here is an R script that uses Armadillo to decompose a large matrix and print | the first 10 eigenvalues. | | library(RcppArmadillo) | library(Rcpp) | | src <- | r"(#include <RcppArmadillo.h> | | // [[Rcpp::depends(RcppArmadillo)]] | | // [[Rcpp::export]] | arma::vec getEigenValues(arma::mat M) { | return arma::eig_sym(M); | })" | | size <- 10000 | m <- matrix(rnorm(size^2), size, size) | m <- m * t(m) | | # This line compiles the above code with the -fopenmp flag. | sourceCpp(code = src, verbose = TRUE, rebuild = TRUE) | result <- getEigenValues(m) | print(result[1:10]) | | When I run this code on server A, I see that arma can implicitly leverage all | available cores by running top -H. However, on server B it can only use one | core despite multiple being available: there is just one process entry in top | -H. Both processes successfully exit and return an answer. The process on | server B is of course much slower.
It is documented in the package how this is applied and the policy is to NOT blindly enforce one use case (say all cores, or half, or a magically chosen value of N for whatever value of N) but to follow the local admin setting and respecting standard environment variables. So I suspect that your machine 'B' differs from machine 'A' in this regards. Not that this is a _run-time_ and not _compile-time_ behavior. As it is for multicore-enabled LAPACK and BLAS libraries, the OpenMP library and basically most software of this type. You can override it, see RcppArmadillo::armadillo_set_number_of_omp_threads RcppArmadillo::armadillo_get_number_of_omp_threads Can you try and see if these help you? Dirk | Here is the compilation on server A: | /usr/local/lib/R/bin/R CMD SHLIB --preclean -o 'sourceCpp_2.so' | 'file197c21cbec564.cpp' | g++ -std=gnu++11 -I"/usr/local/lib/R/include" -DNDEBUG -I../inst/include | -fopenmp -I"/usr/local/lib/R/site-library/Rcpp/include" -I"/usr/local/lib/R/ | site-library/RcppArmadillo/include" -I"/tmp/RtmpwhGRi3/ | sourceCpp-x86_64-pc-linux-gnu-1.0.9" -I/usr/local/include -fpic -g -O2 | -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time | -D_FORTIFY_SOURCE=2 -g -c file197c21cbec564.cpp -o file197c21cbec564.o | g++ -std=gnu++11 -shared -L/usr/local/lib/R/lib -L/usr/local/lib -o | sourceCpp_2.so file197c21cbec564.o -fopenmp -llapack -lblas -lgfortran -lm | -lquadmath -L/usr/local/lib/R/lib -lR | | and here it is for server B: | /sw/R/R-4.2.3/lib64/R/bin/R CMD SHLIB --preclean -o 'sourceCpp_2.so' | 'file158165b9c4ae1.cpp' | g++ -std=gnu++11 -I"/sw/R/R-4.2.3/lib64/R/include" -DNDEBUG -I../inst/include | -fopenmp -I"/home/my_username/.R/library/Rcpp/include" -I"/home/ my_username | /.R/library/RcppArmadillo/include" -I"/tmp/RtmpvfPt4l/ | sourceCpp-x86_64-pc-linux-gnu-1.0.10" -I/usr/local/include -fpic -g -O2 -c | file158165b9c4ae1.cpp -o file158165b9c4ae1.o | g++ -std=gnu++11 -shared -L/sw/R/R-4.2.3/lib64/R/lib -L/usr/local/lib64 -o | sourceCpp_2.so file158165b9c4ae1.o -fopenmp -llapack -lblas -lgfortran -lm | -lquadmath -L/sw/R/R-4.2.3/lib64/R/lib -lR | | I thought that the -fopenmp flag should let arma implicitly parallelize matrix | computations. Any hints as to why this may not work on server B? | | The actual code I'm running is an R package that includes RcppArmadillo and | RcppEnsmallen. Server B is the login node to an hpc cluster, but the code does | not use all cores on the compute nodes either. | | Best, | Robin | _______________________________________________ | Rcpp-devel mailing list | Rcpp-devel@lists.r-forge.r-project.org | https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel -- dirk.eddelbuettel.com | @eddelbuettel | e...@debian.org _______________________________________________ Rcpp-devel mailing list Rcpp-devel@lists.r-forge.r-project.org https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel