So, I have this PoC patch below on top of this patch series for some months now; actually this series was all fallout from working on this patch. It makes 'make -j<N> coccicheck' much faster (speedup of over 99% :) in some scenarios that, in my experience, occur rather frequently when working on Coccinelle semantic patches (as opposed to occasionally running 'make coccicheck' to see whether there are any regressions).
However, it's not ready for inclusion as it is, because, unfortunately, the improvements are not without some disadvantages, as explained in the second half of the commit message below. Anyway, I'm sending this out, because I don't see how I could make it any better, but other contributors working on semantic patches might still find it useful to keep this in their own fork, even in its current form. And perhaps someone will come up with a brilliant idea to address those disadvantages... Also available at: https://github.com/szeder/git make-coccicheck-finegrained -- >8 -- Subject: [PATCH] [PoC] coccinelle: make Coccinelle-related make targets more fine-grained When running 'make coccicheck', each semantic patch is applied to all source files in a separate shell for loop. This approach has the following disadvantages: 1. Even if you only modified a single C source file, that shell loop will still iterate over all source files and apply the semantic patches to all of them, wasting a lot of time. 2. If you apply only a single semantic patch (either implicitly, after you modified only one of them (and the results of the previous 'make coccicheck' are still there), or explicitly, by running e.g. 'make contrib/coccinelle/array.cocci.patch'), then you won't be able to exploit multiple CPU cores to speed up the operation, because that shell loop will iterate over all source files sequentially. 3. 'make coccicheck' can only use as many parallel jobs as the number of semantic patches, so even if you have more available CPU cores than that, you can't exploit them all to speed up this operation. 4. During 'make coccicheck' there is only a single SPATCH contrib/coccinelle/<whatever>.cocci line (or as many lines as the number of parallel jobs) of output when starting to apply each semantic patch, and then comes a long silence without any indication of progress, because applying some of our semantic patches to all source files can take over a minute. This can trick developers new to semantic patches into thinking that something went wrong, hung, ended up in an endless loop, etc. It certainly confused my the first time. Let's add a bit of Makefile metaprogramming to generate finer-grained make targets applying one semantic patch to only a single source file, and specify these as dependencies of the targets applying one semantic patch to all source files. This way that shell loop can be avoided, semantic patches will only be applied to changed source files, and the same semantic patch can be applied in parallel to multiple source files. The only remaining sequential part is aggregating the suggested transformations from the individual targets into a single patch file, which is comparatively cheap (especially since ideally there aren't any suggestions). This change brings spectacular speedup in the scenario described in point (1) above. When the results of a previous 'make coccicheck' are there, the time needed to run touch apply.c ; time make -j4 coccicheck went from 3m42s to 1.848s, which is just over 99% speedup, yay!, and 'apply.c' is the second longest source file in our codebase. In the scenario in point (2), running touch contrib/coccinelle/array.cocci ; time make -j4 coccicheck went from 56.364s to 35.883s, which is ~36% speedup. All the above timings are best-of-five on a machine with 2 physical and 2 logical cores. I don't have the hardware to bring any numbers for point (3). The time needed to run 'make -j4 coccicheck' in a clean state didn't change, it's ~3m42s both with and without this patch. Unfortunately, this new approach has some disadvantages compared to the current situation: - [RFC] With this patch 'make coccicheck's output will look like this ('make' apparently doesn't iterate over semantic patches in lexicographical order): SPATCH commit.cocci abspath.c SPATCH commit.cocci advice.c <... lots of lines ...> SPATCH array.cocci http-walker.c SPATCH array.cocci remote-curl.c which means that the number of lines in the output grows from "Nr-of-semantic-patches" to "Nr-of-semantic-patches * Nr-of-source-files". Now, while this certainly addresses point (4) above, it can be considered too much, and I'm not sure that (4) is that big an issue to justify this much output. OTOH, I couldn't yet figure out a way to print a single 'SPATCH contrib/coccinelle/<whatever>.cocci' line at the beginning of applying that semantic patch without triggering unnecessary work, effectively killing most of the runtime benefits. Or to somehow iterate over source files in the outer loop and over semantic patches in the inner loop, so we could have one output line per file. - [RFC] The overhead of applying a semantic patch to all source files became larger. 'make coccicheck' currently runs only one shell process and creates two output files for each semantic patch. With this patch it will run approx. "Nr-of-semantic-patches * Nr-of-source-files" shell processes and create twice as many output files. This overhead can be quantified by measuring the runtime of: make -j4 SPATCH=true coccicheck and this patch increases it from 0.142s to 1.479s. While this is indeed an order of magnitude increase, it's still negligible compared to the "real" runtime of 3m42s. So the increased overhead doesn't seem to matter on Linux, but I would expect that it's worse on OSX and Windows; though I'm not sure whether Coccinelle (with all its OCaml dependencies) works on those platforms in the first place. - [RFC] This approach uses $(eval), which we haven't used in any of our Makefiles yet. I wonder whether it's portable enough. And it's ugly and complicated. Signed-off-by: SZEDER Gábor <szeder....@gmail.com> --- Makefile | 52 ++++++++++++++++++++++++----------- contrib/coccinelle/.gitignore | 3 +- 2 files changed, 38 insertions(+), 17 deletions(-) diff --git a/Makefile b/Makefile index d616c04125..f516dd93d1 100644 --- a/Makefile +++ b/Makefile @@ -2674,25 +2674,44 @@ COCCI_SOURCES = $(filter-out sha1collisiondetection/%,$(C_SOURCES)) else COCCI_SOURCES = $(filter-out sha1dc/%,$(C_SOURCES)) endif +COCCI_SEM_PATCHES = $(wildcard contrib/coccinelle/*.cocci) -%.cocci.patch: %.cocci $(COCCI_SOURCES) - @echo ' ' SPATCH $<; \ - ret=0; \ - for f in $(COCCI_SOURCES); do \ - $(SPATCH) --sp-file $< $$f $(SPATCH_FLAGS) || \ - { ret=$$?; break; }; \ - done >$@+ 2>$@.log; \ - if test $$ret != 0; \ +define cocci_template +$(cocci_sem_patch)_dirs := $$(addprefix $(cocci_sem_patch).patches/,$$(sort $$(dir $$(COCCI_SOURCES)))) + +$$($(cocci_sem_patch)_dirs): + @mkdir -p $$@ + +# e.g. 'contrib/coccinelle/strbuf.cocci.patches/builtin/commit.c.patch' +# Applies one semantic patch to _one_ source file. +$(cocci_sem_patch).patches/%.patch: % $(cocci_sem_patch) + @printf ' SPATCH %-25s %s\n' $$(notdir $(cocci_sem_patch)) $$<; \ + if ! $$(SPATCH) --sp-file $(cocci_sem_patch) $$< $$(SPATCH_FLAGS) >$$@ 2>$$@.log; \ then \ - cat $@.log; \ + rm -f $$@; \ + cat $$@.log; \ exit 1; \ - fi; \ - mv $@+ $@; \ - if test -s $@; \ - then \ - echo ' ' SPATCH result: $@; \ fi -coccicheck: $(addsuffix .patch,$(wildcard contrib/coccinelle/*.cocci)) + +# e.g. 'contrib/coccinelle/strbuf.cocci.patch' +# Applies one semantic patch to _all_ source files. +$(cocci_sem_patch).patch: $(cocci_sem_patch) $$($(cocci_sem_patch)_dirs) $$(patsubst %,$(cocci_sem_patch).patches/%.patch,$(COCCI_SOURCES)) + @>$$@+; \ + for f in $$(filter %.patch,$$^); do \ + if test -s $$$$f; \ + then \ + cat $$$$f >>$$@+; \ + fi \ + done; \ + mv $$@+ $$@; \ + if test -s $$@; then \ + echo ' ' SPATCH result: $$@; \ + fi +endef + +$(foreach cocci_sem_patch,$(COCCI_SEM_PATCHES),$(eval $(cocci_template))) + +coccicheck: $(addsuffix .patch,$(COCCI_SEM_PATCHES)) .PHONY: coccicheck @@ -2907,7 +2926,8 @@ profile-clean: $(RM) $(addsuffix *.gcno,$(addprefix $(PROFILE_DIR)/, $(object_dirs))) cocciclean: - $(RM) contrib/coccinelle/*.cocci.patch* + $(RM) contrib/coccinelle/*.cocci.patch + $(RM) -r contrib/coccinelle/*.cocci.patches/ clean: profile-clean coverage-clean cocciclean $(RM) *.res diff --git a/contrib/coccinelle/.gitignore b/contrib/coccinelle/.gitignore index d3f29646dc..7ae6ffa983 100644 --- a/contrib/coccinelle/.gitignore +++ b/contrib/coccinelle/.gitignore @@ -1 +1,2 @@ -*.patch* +*.cocci.patch +*.cocci.patches/ -- 2.18.0.408.g42635c01bc
