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coccicheck: optionally batch spatch invocations

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In our "make coccicheck" rule, we currently feed each source file to its
own individual invocation of spatch. This has a few downsides:

  - it repeats any overhead spatch has for starting up and reading the
    patch file

  - any included header files may get processed from multiple
    invocations. This is slow (we see the same header files multiple
    times) and may produce a resulting patch with repeated hunks (which
    cannot be applied without further cleanup)

Ideally we'd just invoke a single instance of spatch per rule-file and
feed it all source files. But spatch can be rather memory hungry when
run in this way. I measured the peak RSS going from ~90MB for a single
file to ~1900MB for all files. Multiplied by multiple rule files being
processed at the same time (for "make -j"), this can make things slower
or even cause them to fail (e.g., this is reported to happen on our
Travis builds).

Instead, let's provide a tunable knob. We'll leave the default at "1",
but it can be cranked up to "999" for maximum CPU/memory tradeoff, or
people can find points in between that serve their particular machines.

Here are a few numbers running a single rule via:

  SIZES='1 4 16 999'
  RULE=contrib/coccinelle/object_id.cocci
  for i in $SIZES; do
    make clean
    /usr/bin/time -o $i.out --format='%e | %U | %S | %M' \
      make $RULE.patch SPATCH_BATCH_SIZE=$i
  done
  for i in $SIZES; do
    printf '%4d | %s\n' $i "$(cat $i.out)"
  done

which yields:

     1 | 97.73 | 93.38 | 4.33 | 100128
     4 | 52.80 | 51.14 | 1.69 | 135204
    16 | 35.82 | 35.09 | 0.76 | 284124
   999 | 23.30 | 23.13 | 0.20 | 1903852

The implementation is done with xargs, which should be widely available;
it's in POSIX, we rely on it already in the test suite. And "coccicheck"
is really a developer-only tool anyway, so it's not a big deal if
obscure systems can't run it.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King 2019-05-06 19:43:34 -04:00 committed by Junio C Hamano
parent 83232e3864
commit 960154b9c1
1 changed files with 6 additions and 7 deletions
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13
Makefile
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@ -1174,8 +1174,10 @@ PTHREAD_CFLAGS =
SPARSE_FLAGS ?=
SP_EXTRA_FLAGS =
# For the 'coccicheck' target
# For the 'coccicheck' target; setting SPATCH_BATCH_SIZE higher will
# usually result in less CPU usage at the cost of higher peak memory.
SPATCH_FLAGS = --all-includes --patch .
SPATCH_BATCH_SIZE = 1
include config.mak.uname
-include config.mak.autogen
@ -2790,12 +2792,9 @@ endif
%.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; \
if ! echo $(COCCI_SOURCES) | xargs -n $(SPATCH_BATCH_SIZE) \
$(SPATCH) --sp-file $< $(SPATCH_FLAGS) \
>$@+ 2>$@.log; \
then \
cat $@.log; \
exit 1; \