git/shared.mak
Ævar Arnfjörð Bjarmason 0b6d0bc924 Makefiles: add and use wildcard "mkdir -p" template
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>
2022-03-03 14:14:55 -08:00

104 lines
2.9 KiB
Makefile

### Remove GNU make implicit rules
## This speeds things up since we don't need to look for and stat() a
## "foo.c,v" every time a rule referring to "foo.c" is in play. See
## "make -p -f/dev/null | grep ^%::'".
%:: %,v
%:: RCS/%,v
%:: RCS/%
%:: s.%
%:: SCCS/s.%
## Likewise delete default $(SUFFIXES). See:
##
## info make --index-search=.SUFFIXES
.SUFFIXES:
### Flags affecting all rules
# A GNU make extension since gmake 3.72 (released in late 1994) to
# remove the target of rules if commands in those rules fail. The
# default is to only do that if make itself receives a signal. Affects
# all targets, see:
#
# info make --index-search=.DELETE_ON_ERROR
.DELETE_ON_ERROR:
### Global variables
## comma, empty, space: handy variables as these tokens are either
## special or can be hard to spot among other Makefile syntax.
comma := ,
empty :=
space := $(empty) $(empty)
### Quieting
## common
QUIET_SUBDIR0 = +$(MAKE) -C # space to separate -C and subdir
QUIET_SUBDIR1 =
ifneq ($(findstring w,$(MAKEFLAGS)),w)
PRINT_DIR = --no-print-directory
else # "make -w"
NO_SUBDIR = :
endif
ifneq ($(findstring s,$(MAKEFLAGS)),s)
ifndef V
## common
QUIET_SUBDIR0 = +@subdir=
QUIET_SUBDIR1 = ;$(NO_SUBDIR) echo ' ' SUBDIR $$subdir; \
$(MAKE) $(PRINT_DIR) -C $$subdir
QUIET = @
QUIET_GEN = @echo ' ' GEN $@;
QUIET_MKDIR_P_PARENT = @echo $(wspfx_SQ) MKDIR -p $(@D);
## Used in "Makefile"
QUIET_CC = @echo ' ' CC $@;
QUIET_AR = @echo ' ' AR $@;
QUIET_LINK = @echo ' ' LINK $@;
QUIET_BUILT_IN = @echo ' ' BUILTIN $@;
QUIET_LNCP = @echo ' ' LN/CP $@;
QUIET_XGETTEXT = @echo ' ' XGETTEXT $@;
QUIET_MSGFMT = @echo ' ' MSGFMT $@;
QUIET_GCOV = @echo ' ' GCOV $@;
QUIET_SP = @echo ' ' SP $<;
QUIET_HDR = @echo ' ' HDR $(<:hcc=h);
QUIET_RC = @echo ' ' RC $@;
QUIET_SPATCH = @echo ' ' SPATCH $<;
## Used in "Documentation/Makefile"
QUIET_ASCIIDOC = @echo ' ' ASCIIDOC $@;
QUIET_XMLTO = @echo ' ' XMLTO $@;
QUIET_DB2TEXI = @echo ' ' DB2TEXI $@;
QUIET_MAKEINFO = @echo ' ' MAKEINFO $@;
QUIET_DBLATEX = @echo ' ' DBLATEX $@;
QUIET_XSLTPROC = @echo ' ' XSLTPROC $@;
QUIET_GEN = @echo ' ' GEN $@;
QUIET_STDERR = 2> /dev/null
QUIET_LINT_GITLINK = @echo ' ' LINT GITLINK $<;
QUIET_LINT_MANSEC = @echo ' ' LINT MAN SEC $<;
QUIET_LINT_MANEND = @echo ' ' LINT MAN END $<;
export V
endif
endif
### Templates
## mkdir_p_parent: lazily "mkdir -p" the path needed for a $@
## file. Uses $(wildcard) to avoid the "mkdir -p" if it's not
## needed.
##
## Is racy, but in a good way; we might redundantly (and safely)
## "mkdir -p" when running in parallel, but won't need to exhaustively create
## individual rules for "a" -> "prefix" -> "dir" -> "file" if given a
## "a/prefix/dir/file". This can instead be inserted at the start of
## the "a/prefix/dir/file" rule.
define mkdir_p_parent_template
$(if $(wildcard $(@D)),,$(QUIET_MKDIR_P_PARENT)$(shell mkdir -p $(@D)))
endef