From b4a5074609596d4c75b32b490d963dc14253a22c Mon Sep 17 00:00:00 2001
From: dim <dim@FreeBSD.org>
Date: Wed, 9 Apr 2014 18:16:58 +0000
Subject: MFC r263778:

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.

I tested this on a 24-core machine, with make -j48 buildworld (N = 6):

		before    stddev       after    stddev
		=======   ======       =======  ======
real time        1741.1     16.5         959.8     2.7
user time       12468.7     16.4       14393.0    16.8
sys  time        1825.0     54.8        2110.6    22.8

(user+sys)/real     8.2                   17.1

E.g. the build was approximately 45% faster in real time.  On machines
with less cores, or with lower -j settings, the speedup will not be as
impressive.  But at least you can now almost max out a machine with
buildworld!

Submitted by:	jilles

MFC r263833:

Enable parallel building for gnu/usr.bin and usr.bin/clang too.
---
 share/mk/bsd.subdir.mk | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

(limited to 'share/mk')

diff --git a/share/mk/bsd.subdir.mk b/share/mk/bsd.subdir.mk
index 12dd4de..0ceda56 100644
--- a/share/mk/bsd.subdir.mk
+++ b/share/mk/bsd.subdir.mk
@@ -71,7 +71,26 @@ ${SUBDIR}: .PHONY .MAKE
 .for __target in all all-man checkdpadd clean cleandepend cleandir \
     cleanilinks depend distribute lint maninstall manlint obj objlink \
     realinstall regress tags ${SUBDIR_TARGETS}
+.ifdef SUBDIR_PARALLEL
+.for __dir in ${SUBDIR}
+${__target}: ${__target}_subdir_${__dir}
+${__target}_subdir_${__dir}: .MAKE
+	@${_+_}set -e; \
+		if test -d ${.CURDIR}/${__dir}.${MACHINE_ARCH}; then \
+			${ECHODIR} "===> ${DIRPRFX}${__dir}.${MACHINE_ARCH} (${__target:realinstall=install})"; \
+			edir=${__dir}.${MACHINE_ARCH}; \
+			cd ${.CURDIR}/$${edir}; \
+		else \
+			${ECHODIR} "===> ${DIRPRFX}${__dir} (${__target:realinstall=install})"; \
+			edir=${__dir}; \
+			cd ${.CURDIR}/$${edir}; \
+		fi; \
+		${MAKE} ${__target:realinstall=install} \
+		    DIRPRFX=${DIRPRFX}$$edir/
+.endfor
+.else
 ${__target}: _SUBDIR
+.endif
 .endfor
 
 .for __target in files includes
-- 
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