Date: Fri, 23 May 2014 14:37:37 +0200 From: Andreas Nilsson <andrnils@gmail.com> To: Ian Lepore <ian@freebsd.org> Cc: Dimitry Andric <dim@freebsd.org>, stable@freebsd.org, Luigi Rizzo <rizzo@iet.unipi.it> Subject: Re: build order race after SUBDIR_PARALLEL (264303) Message-ID: <CAPS9%2BSvaStD9C8n282Nf1=dLrx3CkbRUw1ew6-MDfrOE0_Kp-g@mail.gmail.com> In-Reply-To: <1400848012.1152.311.camel@revolution.hippie.lan> References: <20140523065653.GA86035@onelab2.iet.unipi.it> <1400848012.1152.311.camel@revolution.hippie.lan>
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On Fri, May 23, 2014 at 2:26 PM, Ian Lepore <ian@freebsd.org> wrote: > On Fri, 2014-05-23 at 08:56 +0200, Luigi Rizzo wrote: > > Hi, > > I have recently hit a problem when building stable/10 with > > "make -j 8" which i tracked down to svn 264303, the > > MFC of the SUBDIR_PARALLEL build feature. > > > > With a large number of parallel tasks (and GCC; > > it is a race condition so timing matters), the build fails > > during the toolchain target with this: > > > > --- sig_party.o --- > > cc -O2 -pipe > -I/usr/home/luigi/FreeBSD/R10/lib/libngatm/../../sys/contrib/ngatm > -I/usr/home/luigi/FreeBSD/R10/../usr/obj-pico-amd64/usr/home/luigi/FreeBSD/R10/lib/libngatm > > -I/usr/home/luigi/FreeBSD/R10/lib/libngatm/../../contrib/ngatm/libngatm > -std=gnu99 -fstack-protector -Wsystem-headers -Werror -Wall > -Wno-format-y2k -W -Wno-unused-parameter - > > Wstrict-prototypes -Wmissing-prototypes -Wpointer-arith -Wreturn-type > -Wcast-qual -Wwrite-strings -Wswitch -Wshadow -Wunused-parameter > -Wcast-align -Wchar-subscripts -Winline > > -Wnested-externs -Wredundant-decls -Wold-style-definition > -Wno-pointer-sign -c > /usr/home/luigi/FreeBSD/R10/lib/libngatm/../../sys/contrib/ngatm/netnatm/sig/sig_party.c > -o sig_ > > party.o > > --- all_subdir_libproc --- > > > /usr/home/luigi/FreeBSD/R10/../usr/obj-pico-amd64/usr/home/luigi/FreeBSD/R10/tmp/usr/bin/ld: > cannot find -lsupc++ > > *** [libproc.so.2] Error code 1 > > > > make[5]: stopped in /usr/home/luigi/FreeBSD/R10/lib/libproc > > 1 error > > ... > > > > > > Turns out that before SUBDIR_PARALLEL, libsupc++ was built > > before libproc thus satisfying the dependency; but with > > -j XXX we cannot guarantee the ordering and there is no > > explicit constraint or .ORDER in the makefiles to build > > things in the correct order. > > > > This is a race condition so you may or may not see the problem > > depending on what you are building and where. > > > > I am seeing the problem consistently on stable/10 after 264303 > > when building toolchain with GCC (not clang) on an 8-core machine > > and make -j 8 > > > > Building the above with -j 4 seem to work fine, > > as it works building HEAD with -j 8 > > > > cheers > > luigi > > Aha. I asked for exactly this info on the commit list (so you can > ignore that request). Warner & I kicked around some ideas on how to > solve this a while back, I'll see if I can make some progress towards > better dependency controls for SUBDIR_PARALLEL this weekend. > > -- Ian > > > Sorry for a perhaps a cheeky question, but is this not all due to not telling make the dependencies, and/or due to "recursive" make? When is decided to learn make (although that was mainly gnu make ) I found the following http://aegis.sourceforge.net/auug97.pdf very enlightening. I do realise that such a redesign is a tremendous effort. Best regards Andreas
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