[R-pkg-devel] Too many cores used in examples (not caused by data.table)

? Thu, 19 Oct 2023 05:57:54 +0000
"Helske, Jouni" <jouni.helske at jyu.fi> ?????:

But I just realised that bssm uses Armadillo via RcppArmadillo, which
uses OpenMP by default for some elementwise operations. So, I wonder
if that could be the culprit?

I wasn't able to reproduce the NOTE either, despite manually setting
the environment variable
_R_CHECK_EXAMPLE_TIMING_CPU_TO_ELAPSED_THRESHOLD=2 before running R CMD
check, but I think I can see the code using OpenMP. Here's what I did:

0. Temporarily lower the system protections against capturing
performance traces of potentially sensitive parts:

echo -1 | sudo tee /proc/sys/kernel/perf_event_paranoid

(Set it back to 3 after you're done.)

1. Run the following command with the development version of the
package installed:

env OPENBLAS_NUM_THREADS=1 \
 perf record --call-graph drawf,4096 \
 R -e 'library(bssm); system.time(replicate(100, example(exchange)))'

OPENBLAS_NUM_THREADS=1 will prevent OpenBLAS from spawning worker
threads if you have it installed. (A different BLAS may need different
environment variables.)

2. Run `perf report` and browse collected call stack information.

The call stacks are hard to navigate, but I think they are not pointing
towards Armadillo. At least, setting ARMA_OPENMP_THREADS=1 doesn't
help, but setting OMP_THREAD_LIMIT=1 does.

Best regards,
Ivan