[gentoo-user] Re: "emerge --jobs=1 ..." vs "MAKEOPTS=-j1 emerge ..."

["Holger Hoffstätte" <holger@applied-asynchrony.com>]

On 2020-06-21 11:53, Dr Rainer Woitok wrote:
> Greetings,
> 
> is there any difference between running "emerge --jobs=1 ..."  and runn-
> ing "MAKEOPTS=-j1 emerge ..."?

--jobs=1 starts one package build at a time, possibly using many parallel
processes - depending on MAKEOPTS and how the build works.

MAKEOPTS sets the number of parallel processes within one package build.

They are complementary, and you can combine them. However frequently
a series of packages have dependencies (a before b before c), so starting
multiple --jobs may not have any effect. Or it may, e.g. in the case of
rebuilds or independent packages that often only use one process to build,
e.g. perl modules or something smaller. --jobs can really make a difference
since otherwise you would suffer from portage/script/shell overhead relative
to the actual work being performed.

make offers the -l parameter that constrains the number of processes by
load, and adjusts them accordingly. As an example, with 8 cores you could
use MAKEOPTS="-j8 -l8" to enable inter-ebuild parallelism and a max. load
for one package, then start several --jobs to build independent packages
without waiting for each other.

Hope this helps.

-h