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

[Helske, Jouni]

Thanks for the help, I now tried resubmitting with Sys.setenv("OMP_THREAD_LIMIT" = 2) at the top of the exchange example, but I still get the same note:

Examples with CPU time > 2.5 times elapsed time
          user system elapsed ratio
exchange 1.196   0.04   0.159 7.774

Not sure what to try next.

Best,
Jouni
________________________________
From: Ivan Krylov <krylov.r00t using gmail.com>
Sent: Friday, October 20, 2023 16:54
To: Helske, Jouni <jouni.helske using jyu.fi>
Cc: r-package-devel using r-project.org <r-package-devel using r-project.org>
Subject: Re: [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 using 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

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