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Jeff King 2d86a96220 t: avoid sed-based chain-linting in some expensive cases
Commit 878f988350 (t/test-lib: teach --chain-lint to detect broken
&&-chains in subshells, 2018-07-11) introduced additional chain-lint
tests which add an extra "sed" pipeline to each test we run. This has a
measurable impact on runtime. Here are timings with and without a new
environment variable (added by this patch) that lets you disable just
the additional sed-based chain-lint tests:

  Benchmark #1: GIT_TEST_CHAIN_LINT_HARDER=1 make test
    Time (mean ± σ):     64.202 s ±  1.030 s    [User: 622.469 s, System: 301.402 s]
    Range (min … max):   61.571 s … 65.662 s    10 runs

  Benchmark #2: GIT_TEST_CHAIN_LINT_HARDER=0 make test
    Time (mean ± σ):     57.591 s ±  0.333 s    [User: 529.368 s, System: 270.618 s]
    Range (min … max):   57.143 s … 58.309 s    10 runs

  Summary
    'GIT_TEST_CHAIN_LINT_HARDER=0 make test' ran
      1.11 ± 0.02 times faster than 'GIT_TEST_CHAIN_LINT_HARDER=1 make test'

Of course those extra lint checks are doing something useful, so paying
a few extra seconds (at least on Linux) isn't so bad (though note the
CPU time; we're bounded in our parallel run here by the slowest test, so
it really is ~120s of CPU improvement).

But we can observe that there are some test scripts where they produce a
much stronger effect, and provide less value. In t0027 and t3070 we run
a very large number of small tests, all driven by a series of
functions/loops which are filling in the test bodies. There we get much
less bang for our buck in terms of bug-finding versus CPU cost.

This patch introduces a mechanism for controlling when those extra
lint checks are run, at two levels:

  - a user can ask to disable or to force-enable the checks by setting
    GIT_TEST_CHAIN_LINT_HARDER

  - if the user hasn't specified a preference, individual scripts can
    disable the checks by setting GIT_TEST_CHAIN_LINT_HARDER_DEFAULT;
    scripts which don't set that get the current behavior of enabling
    them.

In addition, this patch flips the default for t0027 and t3070's
mass-generated sections to disable the extra checks. Here are the timing
results for t0027:

  Benchmark #1: GIT_TEST_CHAIN_LINT_HARDER=1 ./t0027-auto-crlf.sh
    Time (mean ± σ):     17.078 s ±  0.848 s    [User: 14.878 s, System: 7.075 s]
    Range (min … max):   15.952 s … 18.421 s    10 runs

  Benchmark #2: GIT_TEST_CHAIN_LINT_HARDER=0 ./t0027-auto-crlf.sh
    Time (mean ± σ):      9.063 s ±  0.759 s    [User: 7.890 s, System: 3.362 s]
    Range (min … max):    7.747 s … 10.619 s    10 runs

  Benchmark #3: ./t0027-auto-crlf.sh
    Time (mean ± σ):      9.186 s ±  0.881 s    [User: 7.957 s, System: 3.427 s]
    Range (min … max):    7.796 s … 10.498 s    10 runs

  Summary
    'GIT_TEST_CHAIN_LINT_HARDER=0 ./t0027-auto-crlf.sh' ran
      1.01 ± 0.13 times faster than './t0027-auto-crlf.sh'
      1.88 ± 0.18 times faster than 'GIT_TEST_CHAIN_LINT_HARDER=1 ./t0027-auto-crlf.sh'

We can see that disabling the checks for the whole script buys us an
almost 2x speedup. But the new default behavior, disabling them only for
the mass-generated part, gets us most of that speedup (but still leaves
the checks on for further manual tests people might write).

  As a side note, I'd caution about comparing runtimes and CPU seconds
  between this timing and the earlier "make test" one. In "make test",
  we're running a lot of scripts in parallel, so the CPU is throttling
  down (and thus a CPU second saved here would count for more during a
  parallel run; the same work takes more CPU seconds there).

We get similar results for t3070:

  Benchmark #1: GIT_TEST_CHAIN_LINT_HARDER=1 ./t3070-wildmatch.sh
    Time (mean ± σ):     20.054 s ±  3.967 s    [User: 16.003 s, System: 8.286 s]
    Range (min … max):   11.891 s … 23.671 s    10 runs

  Benchmark #2: GIT_TEST_CHAIN_LINT_HARDER=0 ./t3070-wildmatch.sh
    Time (mean ± σ):     12.399 s ±  2.256 s    [User: 7.542 s, System: 5.342 s]
    Range (min … max):    9.606 s … 15.727 s    10 runs

  Benchmark #3: ./t3070-wildmatch.sh
    Time (mean ± σ):     10.726 s ±  3.476 s    [User: 6.790 s, System: 4.365 s]
    Range (min … max):    5.444 s … 15.376 s    10 runs

  Summary
    './t3070-wildmatch.sh' ran
      1.16 ± 0.43 times faster than 'GIT_TEST_CHAIN_LINT_HARDER=0 ./t3070-wildmatch.sh'
      1.87 ± 0.71 times faster than 'GIT_TEST_CHAIN_LINT_HARDER=1 ./t3070-wildmatch.sh'

Again, we get almost a 2x speedup disabling these. In this case, there
are no tests not covered by the script's "default to disable" behavior,
so the second two benchmarks should be the same (and while they do
differ, you can see the variance is quite high but they're within one
standard deviation).

So it seems like for these two scripts, at least, disabling the extra
checks is a reasonable tradeoff. Sadly, the overall runtime of "make
test" on my system doesn't get much faster. But that's because we're
mostly limited by the cost of the single biggest test. Here are the
top-5 tests by wall-clock time from a parallel run, before my patch:

  57.9192368984222 t9001-send-email.sh
  45.6329638957977 t0027-auto-crlf.sh
  32.5278220176697 t3070-wildmatch.sh
  22.2701289653778 t7610-mergetool.sh
  20.8635759353638 t1701-racy-split-index.sh

And after:

  57.1476998329163 t9001-send-email.sh
  33.776211977005 t0027-auto-crlf.sh
  21.3116669654846 t7610-mergetool.sh
  20.7748689651489 t1701-racy-split-index.sh
  19.6957249641418 t7112-reset-submodule.sh

We dropped 12s from t0027, and t3070 dropped off our list entirely at
around 16s. In both cases we're bound by t9001, but its slowness is
due to the actual tests, so we'll have to deal with it in a different
way. But this reduces overall CPU, and means that dealing with t9001 (by
improving the speed of send-email or splitting it apart) will let us
reduce our overall runtime even on multi-core machines.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2021-05-13 15:50:44 +09:00
.github
Documentation Git 2.31.1 2021-03-26 14:49:41 -07:00
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t t: avoid sed-based chain-linting in some expensive cases 2021-05-13 15:50:44 +09:00
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abspath.c
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add-interactive.h
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advice.c
advice.h
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alias.h
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alloc.h
apply.c
apply.h
archive-tar.c
archive-zip.c
archive.c
archive.h
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attr.h
banned.h
base85.c
bisect.c
bisect.h
blame.c
blame.h
blob.c
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bloom.c
bloom.h
branch.c
branch.h
builtin.h
bulk-checkin.c
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bundle.c
bundle.h
cache-tree.c
cache-tree.h
cache.h
chdir-notify.c
chdir-notify.h
check-builtins.sh
check_bindir
checkout.c
checkout.h
chunk-format.c
chunk-format.h
color.c
color.h
column.c
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combine-diff.c
command-list.txt
commit-graph.c
commit-graph.h
commit-reach.c
commit-reach.h
commit-slab-decl.h
commit-slab-impl.h
commit-slab.h
commit.c
commit.h
common-main.c
config.c
config.h
config.mak.dev
config.mak.in
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configure.ac
connect.c
connect.h
connected.c
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convert.c
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copy.c
credential.c
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csum-file.c
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ctype.c
daemon.c
date.c
decorate.c
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delta-islands.c
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delta.h
detect-compiler
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diff-lib.c
diff-merges.c
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diff-no-index.c
diff.c
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diffcore-break.c
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list-objects-filter-options.c
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lockfile.c
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log-tree.c
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ls-refs.c
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mailinfo.c
mailinfo.h
mailmap.c
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match-trees.c
mem-pool.c
mem-pool.h
merge-blobs.c
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merge-ort-wrappers.c
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merge-ort.c
merge-ort.h
merge-recursive.c
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merge.c
mergesort.c
mergesort.h
midx.c
midx.h
name-hash.c
notes-cache.c
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stable-qsort.c
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strmap.h
strvec.c
strvec.h
sub-process.c
sub-process.h
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tempfile.c
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tmp-objdir.c
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usage.c
userdiff.c
userdiff.h
utf8.c
utf8.h
varint.c
varint.h
version.c
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walker.h
wildmatch.c
wildmatch.h
worktree.c
worktree.h
wrap-for-bin.sh
wrapper.c
write-or-die.c
ws.c
wt-status.c
wt-status.h
xdiff-interface.c
xdiff-interface.h
zlib.c

README.md

Build status

Git - fast, scalable, distributed revision control system

Git is a fast, scalable, distributed revision control system with an unusually rich command set that provides both high-level operations and full access to internals.

Git is an Open Source project covered by the GNU General Public License version 2 (some parts of it are under different licenses, compatible with the GPLv2). It was originally written by Linus Torvalds with help of a group of hackers around the net.

Please read the file INSTALL for installation instructions.

Many Git online resources are accessible from https://git-scm.com/ including full documentation and Git related tools.

See Documentation/gittutorial.txt to get started, then see Documentation/giteveryday.txt for a useful minimum set of commands, and Documentation/git-<commandname>.txt for documentation of each command. If git has been correctly installed, then the tutorial can also be read with man gittutorial or git help tutorial, and the documentation of each command with man git-<commandname> or git help <commandname>.

CVS users may also want to read Documentation/gitcvs-migration.txt (man gitcvs-migration or git help cvs-migration if git is installed).

The user discussion and development of Git take place on the Git mailing list -- everyone is welcome to post bug reports, feature requests, comments and patches to git@vger.kernel.org (read Documentation/SubmittingPatches for instructions on patch submission). To subscribe to the list, send an email with just "subscribe git" in the body to majordomo@vger.kernel.org. The mailing list archives are available at https://lore.kernel.org/git/, http://marc.info/?l=git and other archival sites.

Issues which are security relevant should be disclosed privately to the Git Security mailing list git-security@googlegroups.com.

The maintainer frequently sends the "What's cooking" reports that list the current status of various development topics to the mailing list. The discussion following them give a good reference for project status, development direction and remaining tasks.

The name "git" was given by Linus Torvalds when he wrote the very first version. He described the tool as "the stupid content tracker" and the name as (depending on your mood):

  • random three-letter combination that is pronounceable, and not actually used by any common UNIX command. The fact that it is a mispronunciation of "get" may or may not be relevant.
  • stupid. contemptible and despicable. simple. Take your pick from the dictionary of slang.
  • "global information tracker": you're in a good mood, and it actually works for you. Angels sing, and a light suddenly fills the room.
  • "goddamn idiotic truckload of sh*t": when it breaks