[R-pkg-devel] NOTE: Installation took CPU time 3.5 times elapsed time

[Ivan Krylov]

On Tue, 29 Jul 2025 07:25:46 -0500
Dirk Eddelbuettel <edd using debian.org> wrote:

> But note that my machine has no -flto=$N for
> some N but rather '-flto=auto' which also results in the NOTE.
> 
> So an extra check may be needed to not issue the nag if LTO is used?

You're right, -flto=auto chooses the number of LTO processes
automatically if the Make jobserver is not available. Rven if I set
MAKEFLAGS=-j2 before running R CMD INSTALL, that information is not
propagated to g++, so it runs on all logical processors.

This could be the only way to make GCC use noticeably more than one
process by itself, I couldn't find anything else right now.

As a short-term solution, the "specialChecks" system operated by Prof.
Kurt Hornik can switch to -flto=2. For the more distant future, making
this message "INFO" instead of "NOTE" or possibly raising the limit
when LTO is used could make sense.

-- 
Best regards,
Ivan