`make[1]: warning: -j256 forced in makefile: resetting jobserver mode.`

[paulmenzel]

OpenBLAS 0.3.33, GNU Make 4.4

$ make -j300 DYNAMIC_ARCH=1 NO_LAPACKE=1 PREFIX=/usr EPREFIX=/usr BINDIR=/usr/bin SBINDIR=/usr/sbin LIBEXECDIR=/usr/libexec SYSCONFDIR=/etc SHAREDSTATEDIR=/var LOCALSTATEDIR=/var LIBDIR=/usr/lib INCLUDEDIR=/usr/include DATAROOTDIR=/usr/share DATADIR=/usr/share INFODIR=/usr/share/info LOCALEDIR=/usr/share/locale MANDIR=/usr/share/man DOCDIR=/usr/share/doc/openblas
make[1]: Entering directory '/dev/shm/bee-pmenzel/openblas/openblas-0.3.33-0/source/interface'
make[1]: warning: -j256 forced in makefile: resetting jobserver mode.
[ … repeats for other directories … ]

Unfortunately, I couldn’t find where 256 comes from.

[martin-frbg]

Maybe 256 is an internal limit in (perhaps just your build of) gmake 4.4, or you supplied the -j300 argument while the build system applied its default of "number of cores in the build host" which happened to be 256 ? In any case, this should have no impact on the build.

[paulmenzel]

I use -j300 to build a lot of software, and it’s only shown with OpenBLAS.

[martin-frbg]

Can you try adding MAKE_NB_JOBS=-1 to the command line (as documented in Makefile.rule), in order to disable the builtin method of setting -j ? Otherwise the build system produces its own MAKEFLAGS = -jN setting in the generated Makefile.conf, and you'll get the warning (though as far as I can tell, the "manually" defined "-j" number still wins.

[paulmenzel]

Can you try adding MAKE_NB_JOBS=-1 to the command line (as documented in Makefile.rule), in order to disable the builtin method of setting -j ?

Indeed, that helped.

Otherwise the build system produces its own MAKEFLAGS = -jN setting in the generated Makefile.conf,
and you'll get the warning

Understood. At least for me that wasn’t clear, when reading the comment before reporting the issue:

OpenBLAS/Makefile.rule

Lines 200 to 205 in 662d80b

	# Force number of make jobs. The default is the number of logical CPU of the host.
	# This is particularly useful when using distcc.
	# A negative value will disable adding a -j flag to make, allowing to use a parent
	# make -j value. This is useful to call OpenBLAS make from an other project
	# makefile
	# MAKE_NB_JOBS = 2

It only talks about parent make, and – at least for me – the normal usage of make with the switch -j is not affected.

(though as far as I can tell, the "manually" defined "-j" number still wins.

OpenBLAS/getarch.c

Lines 2131 to 2142 in 662d80b

	#ifdef MAKE_NB_JOBS
	#if MAKE_NB_JOBS > 0
	printf("MAKEFLAGS += -j %d\n", MAKE_NB_JOBS);
	#else
	// Let make use parent -j argument or -j1 if there
	// is no make parent
	#endif
	#elif NO_PARALLEL_MAKE==1
	printf("MAKEFLAGS += -j 1\n");
	#else
	printf("MAKEFLAGS += -j %d\n", get_num_cores());
	#endif

It does not look like it. MAKE_NB_JOBS is undefined in my build, and then the last branch takes affect setting -j to get_num_cores().

Thank you for clearing this up, but having to set a variable to get the well established make -j… working as expected is surprising. ;-)

[paulmenzel]

Commit ba024fc (Allow to force the number of parallel make job) introducing this oddity says:

This is particularly useful when using distcc

@jeromerobert, I know it’s over ten years old, but is there really no other way?

[martin-frbg]

Can probably cobble up something using findstring on the contents of MAKEFLAGS to ensure that the MAKE_NB_FLAGS=-1 gets set automatically when there's already a -j in MAKEFLAGS. Not that this was the most pressing shortcoming in OpenBLAS...