[RFC PATCH 0/8] speed up 'make clean'

Approximately five years ago, I stopped building the documentation locally and instead started using the 'pre-built' documentation repos from git://git.kernel.org/pub/scm/git/git-{htmldocs,manpages}.git. I placed them next to the git repository (ie. as siblings) and wrote a script (mk-dist-doc.sh) to reproduce the effect of 'make dist-doc', using git-archive, to place the distribution tarballs at the top of the git repo worktree.

[During the creation of these patches, I actually did a 'make' in the Documentation directory and was surprised that it succeeded! However, it reminded me why I stopped building the docs! :-P ]

This meant that the Documentation directory was essentially unused for build purposes, so that a 'make clean' should have nothing to do in that directory. However, on cygwin, I noticed a long pause during a 'make clean' in that directory and, further, it seemed to be GEN-erating some files! I put an item on my TODO list to take a look at that - during the v2.28.0 cycle, I finally found time to look at this issue! :-D

This patch series is the result. Note that this was mainly about speeding up 'make clean' on cygwin (and the performance numbers in the patches reflect use on cygwin). Tonight, I did some timings on Linux as well, so that I could show this table:

              CYGWIN              LINUX
v2.29.0   23.339s              1.709s
Patch #1  12.364s  -47.02%     0.877s  -48.68%
Patch #2  10.361s  -16.20%     0.805s   -8.21%
Patch #3   8.430s  -18.64%     0.672s  -16.52%
Patch #4   6.454s  -23.44%     0.484s  -27.98%
Patch #5   6.428s   -0.40%     0.503s   +3.93%
Patch #6   6.440s   +0.19%     0.517s   +2.78%
Patch #7   6.430s   -0.16%     0.515s   -0.39%
Patch #8   4.064s  -36.80%     0.322s  -37.48%

         23.339/4.064 = 5.74   1.709/0.322 = 5.31 

Note that patches 5-7 are just preparatory patches for the final patch, and are not expected to show any improvement.

This series is marked RFC because I forgot that 'git-gui' patches need to be separately submitted to Pratyush Yadav, the git-gui maintainer. So, I need to drop patch #4 from this series and submit that to Pratyush (the commit message needs to be re-written as well). Unfortunately, this means that the following commit messages will need to be re-written (and timings re-done).

Also, since this series is based on v2.29.0, I had anticipated some conflicts with the 'rs/dist-doc-with-git-archive' branch when merging this with the 'master', 'next' and 'seen' branches. I have just done a trial merge with each branch and, to my surprise, there were no conflicts and they (auto) merged clean. ;)

However, I can certainly rebase these onto the 'master' branch, if that would be easier to deal with. (There has to be a v2 anyway, so ...)

I should note here that the main idea used in these patches, to use the $(MAKECMDGOALS) variable to conditionally include some files, can be defeated by invoking make with multiple goals. For example, if you were to do 'make clean all', then $(MAKECMDGOALS) would be 'clean all' and not 'clean'.

However, doing so with the top-level Makefile would only negate the effect of the last patch, since all of the sub-makes are issued as 'make -C <dir> clean'. So, all of the conditional includes in patches #1-4 will work as intended (and show the noted improvement).

[Yes, 'cd Documentation; make clean all' will be slower that a doing separate 'make clean; make', but the extra 10s, or so, will be swamped by the documentation build time! ;-) ]

ATB, Ramsay Jones

Ramsay Jones (8):
  Documentation/Makefile: conditionally include doc.dep
  Documentation/Makefile: conditionally include ../GIT-VERSION-FILE
  gitweb/Makefile: conditionally include ../GIT-VERSION-FILE
  git-gui/Makefile: conditionally include GIT-VERSION-FILE
  Makefile: don't try to clean old debian build product
  Makefile: don't use a versioned temp distribution directory
  Makefile: don't delete dist tarballs directly by name
  Makefile: conditionally include GIT-VERSION-FILE

 .gitignore             |  1 +
 Documentation/Makefile |  4 ++++
 Makefile               | 28 +++++++++++++++++++---------
 git-gui/Makefile       |  2 ++
 gitweb/Makefile        |  2 ++
 5 files changed, 28 insertions(+), 9 deletions(-)