Hierarchical make: How to avoid unnecessarily going into certain directories?

[Peng Yu]

Hi,

My questions is how to more efficiently run make in hierarchy of
directories. Let me give the following example to demonstrate what I
mean.

I have the following two directories leaf/ and internal/, each of
which has a Makefile as shown below. Note that the targets in leaf/
don't depend any files that are not in leaf/; targets in internal/
depend on targets in leaf/.

To make sure everything is updated, I have a Makefile (also shown
below). Note that I have to set ".PHONY: leaf/.dir", because GNU Make
has to go into this directory to test if anything need to be made. But
the problem is that GNU Make always go to internal/ to check if
anything need to be updated, even if the time stamps of leaf/.dir and
internal/.dir can be used  to determine if make need to go to
internal/.

I guess this is because that once make has an dependence graph build
internally, it is not going to check if it actually need to update a
rule, but rather it propagates the updates. I'm wondering if there is
a way to change my Makefiles or supply some options to make to avoid
go into internal/ if it is unnecessary?

$ ls leaf/
input1.txt  input2.txt  Makefile
$ ls internal/
Makefile
$ cat leaf/Makefile
.PHONY: all clean

all:.dir
.INTERMEDIATE: all-dir
.dir: all-dir
        touch $@

all-dir: result1.txt
result1.txt: input1.txt
        touch $@

all-dir: result2.txt
result2.txt: input2.txt
        touch $@

clean:
        $(RM) .dir result1.txt result2.txt

$ cat internal/Makefile
.PHONY: all clean

all:.dir
.INTERMEDIATE: all-dir
.dir: all-dir
        touch $@

all-dir: result1.txt
result1.txt: ../leaf/result1.txt
        touch $@

all-dir: result2.txt
result2.txt: ../leaf/result2.txt
        touch $@

clean:
        $(RM) .dir result1.txt result2.txt

$ cat Makefile
.PHONY: all clean

# I need set leaf/.dir as .PHONY, because I always
#       need to go in this directory to test
#       if anything needed to be updated.
#       But internal/.dir is always going to be updated.
#       I think this is because GNU Make doesn't check
# the rule "internal/.dir: leaf/.dir" need be updated or not
# , because it assumes that leaf/.dir is remade so internal/.dir
# should be remade.
#
.PHONY: leaf/.dir
all: leaf/.dir
leaf/.dir:
        $(MAKE) -C $(dir $@)

all: internal/.dir
internal/.dir: leaf/.dir
        $(MAKE) -C $(dir $@)

clean:
        $(MAKE) -C leaf clean; $(MAKE) -C internal clean

$ make
make -C leaf/
make[1]: Entering directory `/tmp/hierachy/leaf'
touch result1.txt
touch result2.txt
touch .dir
make[1]: Leaving directory `/tmp/hierachy/leaf'
make -C internal/
make[1]: Entering directory `/tmp/hierachy/internal'
touch result1.txt
touch result2.txt
touch .dir
make[1]: Leaving directory `/tmp/hierachy/internal'
$ make
make -C leaf/
make[1]: Entering directory `/tmp/hierachy/leaf'
make[1]: Nothing to be done for `all'.
make[1]: Leaving directory `/tmp/hierachy/leaf'
make -C internal/
make[1]: Entering directory `/tmp/hierachy/internal'
make[1]: Nothing to be done for `all'.
make[1]: Leaving directory `/tmp/hierachy/internal'

####
Note that make still goes into internal to check if anything should be
made, even if it doesn't have to.


-- 
Regards,
Peng