On Thu, Nov 18 2021, Mike Hommey wrote: > On Wed, Nov 17, 2021 at 12:52:11PM +0100, Ævar Arnfjörð Bjarmason wrote: >> >> On Wed, Nov 17 2021, Mike Hommey wrote: >> >> > On Wed, Nov 17, 2021 at 10:26:27AM +0100, Ævar Arnfjörð Bjarmason wrote: >> >> >> >> On Wed, Nov 17 2021, Mike Hommey wrote: >> >> >> >> > On Tue, Nov 16, 2021 at 01:00:18PM +0100, Ævar Arnfjörð Bjarmason wrote: >> >> >> 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 >> >> >> 8650c6298c1 (doc lint: make "lint-docs" non-.PHONY, 2021-10-15). >> >> >> >> >> >> As seen in 4c64fb5aad9 (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 thatnoted 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 hyperfine -L rev HEAD~0,HEAD~1 -b 'make -C Documentation lint-docs' -p 'rm -rf Documentation/.build' 'make -C Documentation lint-docs' >> >> >> Benchmark 1: make -C Documentation lint-docs' in 'HEAD~0 >> >> >> Time (mean ± σ): 2.129 s ± 0.011 s [User: 1.840 s, System: 0.321 s] >> >> >> Range (min … max): 2.121 s … 2.158 s 10 runs >> >> >> >> >> >> Benchmark 2: make -C Documentation lint-docs' in 'HEAD~1 >> >> >> Time (mean ± σ): 2.659 s ± 0.002 s [User: 2.306 s, System: 0.397 s] >> >> >> Range (min … max): 2.657 s … 2.662 s 10 runs >> >> >> >> >> >> Summary >> >> >> 'make -C Documentation lint-docs' in 'HEAD~0' ran >> >> >> 1.25 ± 0.01 times faster than 'make -C Documentation 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. >> >> > >> >> > Something else that is racy is that $(wildcard) might be saying the >> >> > directory doesn't exist while there's another make subprocess that has >> >> > already started spawning `mkdir -p` for that directory. >> >> > That doesn't make a huge difference, but you can probably still end up >> >> > with multiple `mkdir -p` runs for the same directory. >> >> > >> >> > I think something like the following could work while avoiding those >> >> > races: >> >> > >> >> > define create_parent_dir_RULE >> >> > $(1): | $(dir $(1)). >> >> > ALL_DIRS += $(dir $(1)) >> >> > endef >> >> > >> >> > define create_parent_dir_TARGET >> >> > $(1)/.: $(dir $(1)). >> >> > echo mkdir $$(@D) >> > >> > erf, s/echo // >> > >> >> > endef >> >> > >> >> > $(eval $(call create_parent_dir_RULE, first/path/file)) >> >> > $(eval $(call create_parent_dir_RULE, second/path/file)) >> >> > # ... >> >> > >> >> > $(foreach dir,$(sort $(ALL_DIRS)),$(eval $(call create_parent_dir_TARGET,$(dir:%/=%)))) >> >> >> >> I think the "race" just isn't a problem, and makes managing this much >> >> simpler. >> >> >> >> I.e. we already rely on "mkdir -p" not failing on an existing directory, >> >> so the case where we redundantly try to create a directory that just got >> >> created by a concurrent process is OK, and as the quoted benchmark shows >> >> is much faster than a similar (but not quite the same as) a >> >> dependency-based implementaiton. >> >> >> >> I haven't implemented your solution, but it seems to be inherently more >> >> complex. >> >> >> >> I.e. with the one I've got you just stick the "mkdir if needed" >> >> one-liner in each rule, with yours you'll need to accumulate things in >> >> ALL_DIRS, and have some foreach somewhere or dependency relationship to >> >> create those beforehand if they're nested, no? >> > >> > For each rule, it would also be a oneliner to add above the rule. The rest >> > would be a prelude and a an epilogue to stick somewhere in the Makefile. >> >> How would that epilogue know to handle cases where we're running "clean" >> or whatever thing doesn't want to create the full set of directories >> we've accumulated in ALL_DIRS while parsing the Makefile? > > The epilogue only adds rules like: > > dir/subdir/.: dir/. > mkdir $(@D) > > As long as those "clean" or whatever rules don't depend on those, > nothing will happen. Ah, I see. I don't see why why this pattern would be preferrable to the $(wildcard) idiom I'm introducing, which doesn't require any boilerplate at all. We've got that in snippet form on the one hand, and then my working patch. I haven't tried to implement what you suggested, but don't see how it wouldn't be the same thing speed-wise as the explicitly enumerated dependiencies I replaced for the lint-docs target. So unless there's something broken etc. about that approach I think we should go forward with it.
