R devel - May 2024 - confint Attempts to Use All Server CPUs by Default

Hello,

Would a less resource-intensive value, such as 1, be a safer default CPU value
for confint? I noticed excessive CPU usage on a I.T. administrator-managed
server which was being three-quarters used by another staff member when the
confidence interval calculation in an R Markdown document suddenly changed from
two seconds to ninety seconds because of competition for CPUs between users.
Also, there is no mention of such parallel processing in ?confint, so it was not
clear at first where to look for performance degradation. It could at least be
described in the manual page so that users would know that export
OPENBLAS_NUM_THREADS=1 is a solution.

--------------------------------------
Dario Strbenac
University of Sydney
Camperdown NSW 2050
Australia

? Tue, 21 May 2024 08:00:11 +0000
Dario Strbenac via R-devel <r-devel at r-project.org> ?????:
> Would a less resource-intensive value, such as 1, be a safer default
> CPU value for confint?
Which confint() method do you have in mind? There is at least four of
them by default in R, and many additional classes could make use of
stats:::confint.default by implementing vcov().
> Also, there is no mention of such parallel processing in ?confint, so
> it was not clear at first where to look for performance degradation.
> It could at least be described in the manual page so that users would
> know that export OPENBLAS_NUM_THREADS=1 is a solution.
There isn't much R can do about the behaviour of the BLAS, because
there is no standard interface to set the number of threads. Some BLASes
(like ATLAS) don't even offer it as a tunable number at all [*].

A system administrator could link the installation of R against
FlexiBLAS [**], provide safe defaults in the environment variables and
educate the users about its tunables [***], but that's a choice just
like it had been a choice to link R against a parallel variant of
OpenBLAS on a shared computer. This is described in R Installation and
Administration, section A.3.1 [****].

-- 
Best regards,
Ivan

[*]
https://math-atlas.sourceforge.net/faq.html#tnum

[**]
https://www.mpi-magdeburg.mpg.de/projects/flexiblas

[***]
https://search.r-project.org/CRAN/refmans/flexiblas/html/flexiblas-threads.html

[****]
https://cran.r-project.org/doc/manuals/R-admin.html#BLAS