On 27 Mar 2014, at 19:12, Jilles Tjoelker <jil...@stack.nl> wrote: > On Thu, Mar 27, 2014 at 11:05:00AM -0600, Warner Losh wrote: >> On Mar 26, 2014, at 4:30 PM, Dimitry Andric <d...@freebsd.org> wrote: >>> Author: dim >>> Date: Wed Mar 26 22:30:38 2014 >>> New Revision: 263778 >>> URL: http://svnweb.freebsd.org/changeset/base/263778 > >>> Log: >>> Add a SUBDIR_PARALLEL option to bsd.subdir.mk, to allow make to process >>> all the SUBDIR entries in parallel, instead of serially. Apply this >>> option to a selected number of Makefiles, which can greatly speed up the >>> build on multi-core machines, when using make -j. > >>> This can be extended to more Makefiles later on, whenever they are >>> verified to work correctly with parallel building. > >> Why not have this ‘opt out’ rather than ‘opt in’ like it is now? Are >> there any known bad dependencies this introduces? > > I'm paranoid about build systems ;) It is easy to add dependencies > across directories and as long as directories are built in sequence, > nothing goes wrong. > > In fact, I had enabled SUBDIR_PARALLEL in sys/modules/Makefile as well, > but this caused mysterious failures with some kernels such as mips > ADM5120.
There are a bunch of other parts that don't really like parallel builds at the moment. For example, gnu/usr.bin/binutils needs its libraries (libbfd.a, etc) built first, before it can link the programs. Similar for gnu/usr.bin/cc, which needs libiberty, libcpp, etc before being able to build the rest of gcc. Most of these cases can hopefully be solved by adding .WAIT targets at strategic points in the SUBDIR lists, but this also needs a bit of extra logic in bsd.subdir.mk. -Dimitry
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