Add a template to do the "mkdir -p" of $(@D) (the parent dir of $@)
for us, and use it for the "make lint-docs" targets I added in
8650c6298c (doc lint: make "lint-docs" non-.PHONY, 2021-10-15).
As seen in 4c64fb5aad (Documentation/Makefile: fix lint-docs mkdir
dependency, 2021-10-26) maintaining these manual lists of parent
directory dependencies is fragile, in addition to being obviously
verbose.
I used this pattern at the time because I couldn't find another method
than "order-only" prerequisites to avoid doing a "mkdir -p $(@D)" for
every file being created, which as noted in [1] would be significantly
slower.
But as it turns out we can use this neat trick of only doing a "mkdir
-p" if the $(wildcard) macro tells us the path doesn't exist. A re-run
of a performance test similar to that noted downthread of [1] in [2]
shows that this is faster, in addition to being less verbose and more
reliable (this uses my "git-hyperfine" thin wrapper for "hyperfine"[3]):
$ git -c hyperfine.hook.setup= hyperfine -L rev HEAD~1,HEAD~0 -s 'make -C Documentation lint-docs' -p 'rm -rf Documentation/.build' 'make -C Documentation -j1 lint-docs'
Benchmark 1: make -C Documentation -j1 lint-docs' in 'HEAD~1
Time (mean ± σ): 2.914 s ± 0.062 s [User: 2.449 s, System: 0.489 s]
Range (min … max): 2.834 s … 3.020 s 10 runs
Benchmark 2: make -C Documentation -j1 lint-docs' in 'HEAD~0
Time (mean ± σ): 2.315 s ± 0.062 s [User: 1.950 s, System: 0.386 s]
Range (min … max): 2.229 s … 2.397 s 10 runs
Summary
'make -C Documentation -j1 lint-docs' in 'HEAD~0' ran
1.26 ± 0.04 times faster than 'make -C Documentation -j1 lint-docs' in 'HEAD~1'
So let's use that pattern both for the "lint-docs" target, and a few
miscellaneous other targets.
This method of creating parent directories is explicitly racy in that
we don't know if we're going to say always create a "foo" followed by
a "foo/bar" under parallelism, or skip the "foo" because we created
"foo/bar" first. In this case it doesn't matter for anything except
that we aren't guaranteed to get the same number of rules firing when
running make in parallel.
1. https://lore.kernel.org/git/211028.861r45y3pt.gmgdl@evledraar.gmail.com/
2. https://lore.kernel.org/git/211028.86o879vvtp.gmgdl@evledraar.gmail.com/
3. https://gitlab.com/avar/git-hyperfine/
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The $(QUIET) variables we define are largely duplicated between our
various Makefiles, let's define them in the new "shared.mak" instead.
Since we're not using the environment to pass these around we don't
need to export the "QUIET_GEN" and "QUIET_BUILT_IN" variables
anymore. The "QUIET_GEN" variable is used in "git-gui/Makefile" and
"gitweb/Makefile", but they've got their own definition for those. The
"QUIET_BUILT_IN" variable is only used in the top-level "Makefile". We
still need to export the "V" variable.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Move these variables over to the shared.mak, we'll make use of them in
a subsequent commit.
Note that there's reason for these to be "simply expanded variables",
i.e. to use ":=" assignments instead of lazily expanded "="
assignments. We could use "=", but let's leave this as-is for now for
ease of review.
See 425ca6710b (Makefile: allow combining UBSan with other
sanitizers, 2017-07-15) for the commit that introduced these.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This was added in 30248886ce (Makefile: disable default implicit
rules, 2010-01-26), let's move it to the top of "shared.mak" so it'll
apply to all our Makefiles.
This doesn't benefit the main Makefile at all, since it already had
the rule, but since we're including shared.mak in other Makefiles
starts to benefit them. E.g. running the 'man" target is now faster:
$ git -c hyperfine.hook.setup= hyperfine -L rev HEAD~1,HEAD~0 -s 'make -C Documentation man' 'make -C Documentation -j1 man'
Benchmark 1: make -C Documentation -j1 man' in 'HEAD~1
Time (mean ± σ): 121.7 ms ± 8.8 ms [User: 105.8 ms, System: 18.6 ms]
Range (min … max): 112.8 ms … 148.4 ms 26 runs
Benchmark 2: make -C Documentation -j1 man' in 'HEAD~0
Time (mean ± σ): 97.5 ms ± 8.0 ms [User: 80.1 ms, System: 20.1 ms]
Range (min … max): 89.8 ms … 111.8 ms 32 runs
Summary
'make -C Documentation -j1 man' in 'HEAD~0' ran
1.25 ± 0.14 times faster than 'make -C Documentation -j1 man' in 'HEAD~1'
The reason for that can be seen when comparing that run with
"--debug=a". Without this change making a target like "git-status.1"
will cause "make" to consider not only "git-status.txt", but
"git-status.txt.o", as well as numerous other implicit suffixes such
as ".c", ".cc", ".cpp" etc. See [1] for a more detailed before/after
example.
So this is causing us to omit a bunch of work we didn't need to
do. For making "git-status.1" the "--debug=a" output is reduced from
~140k lines to ~6k.
1. https://lore.kernel.org/git/220222.86bkyz875k.gmgdl@evledraar.gmail.com/
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Override built-in rules of GNU make that use a wildcard target. This
can speeds things up significantly as we don't need to stat() so many
files. GNU make does that by default to see if it can retrieve their
contents from RCS or SCCS. See [1] for an old mailing list discussion
about how to disable these.
The speed-up may vary. I've seen 1-10% depending on the speed of the
local disk, caches, -jN etc. Running:
strace -f -c -S calls make -j1 NO_TCLTK=Y
Shows that we reduce the number of syscalls we make, mostly in "stat"
calls.
We could also invoke make with "-r" by setting "MAKEFLAGS = -r"
early. Doing so might make us a bit faster still. But doing so is a
much bigger hammer, since it will disable all built-in rules,
some (all?) of which can be seen with:
make -f/dev/null -p | grep -v -e ^# -e ^$
We may have something that relies on them, so let's go for the more
isolated optimization here that gives us most or all of the wins.
1. https://lists.gnu.org/archive/html/help-make/2002-11/msg00063.html
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We have various behavior that's shared across our Makefiles, or that
really should be (e.g. via defined templates). Let's create a
top-level "shared.mak" to house those sorts of things, and start by
adding the ".DELETE_ON_ERROR" flag to it.
See my own 7b76d6bf22 (Makefile: add and use the ".DELETE_ON_ERROR"
flag, 2021-06-29) and db10fc6c09 (doc: simplify Makefile using
.DELETE_ON_ERROR, 2021-05-21) for the addition and use of the
".DELETE_ON_ERROR" flag.
I.e. this changes the behavior of existing rules in the altered
Makefiles (except "Makefile" & "Documentation/Makefile"). I'm
confident that this is safe having read the relevant rules in those
Makfiles, and as the GNU make manual notes that it isn't the default
behavior is out of an abundance of backwards compatibility
caution. From edition 0.75 of its manual, covering GNU make 4.3:
[Enabling '.DELETE_ON_ERROR' is] almost always what you want
'make' to do, but it is not historical practice; so for
compatibility, you must explicitly request it.
This doesn't introduce a bug by e.g. having this
".DELETE_ON_ERROR" flag only apply to this new shared.mak, Makefiles
have no such scoping semantics.
It does increase the danger that any Makefile without an explicit "The
default target of this Makefile is..." snippet to define the default
target as "all" could have its default rule changed if our new
shared.mak ever defines a "real" rule. In subsequent commits we'll be
careful not to do that, and such breakage would be obvious e.g. in the
case of "make -C t".
We might want to make that less fragile still (e.g. by using
".DEFAULT_GOAL" as noted in the preceding commit), but for now let's
simply include "shared.mak" without adding that boilerplate to all the
Makefiles that don't have it already. Most of those are already
exposed to that potential caveat e.g. due to including "config.mak*".
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
