t/perf/README

   1 Git performance tests
   2 =====================
   3
   4 This directory holds performance testing scripts for git tools.  The
   5 first part of this document describes the various ways in which you
   6 can run them.
   7
   8 When fixing the tools or adding enhancements, you are strongly
   9 encouraged to add tests in this directory to cover what you are
  10 trying to fix or enhance.  The later part of this short document
  11 describes how your test scripts should be organized.
  12
  13
  14 Running Tests
  15 -------------
  16
  17 The easiest way to run tests is to say "make".  This runs all
  18 the tests on the current git repository.
  19
  20     === Running 2 tests in this tree ===
  21     [...]
  22     Test                                     this tree
  23     ---------------------------------------------------------
  24     0001.1: rev-list --all                   0.54(0.51+0.02)
  25     0001.2: rev-list --all --objects         6.14(5.99+0.11)
  26     7810.1: grep worktree, cheap regex       0.16(0.16+0.35)
  27     7810.2: grep worktree, expensive regex   7.90(29.75+0.37)
  28     7810.3: grep --cached, cheap regex       3.07(3.02+0.25)
  29     7810.4: grep --cached, expensive regex   9.39(30.57+0.24)
  30
  31 You can compare multiple repositories and even git revisions with the
  32 'run' script:
  33
  34     $ ./run . origin/next /path/to/git-tree p0001-rev-list.sh
  35
  36 where . stands for the current git tree.  The full invocation is
  37
  38     ./run [<revision|directory>...] [--] [<test-script>...]
  39
  40 A '.' argument is implied if you do not pass any other
  41 revisions/directories.
  42
  43 You can also manually test this or another git build tree, and then
  44 call the aggregation script to summarize the results:
  45
  46     $ ./p0001-rev-list.sh
  47     [...]
  48     $ GIT_BUILD_DIR=/path/to/other/git ./p0001-rev-list.sh
  49     [...]
  50     $ ./aggregate.perl . /path/to/other/git ./p0001-rev-list.sh
  51
  52 aggregate.perl has the same invocation as 'run', it just does not run
  53 anything beforehand.
  54
  55 You can set the following variables (also in your config.mak):
  56
  57     GIT_PERF_REPEAT_COUNT
  58         Number of times a test should be repeated for best-of-N
  59         measurements.  Defaults to 3.
  60
  61     GIT_PERF_MAKE_OPTS
  62         Options to use when automatically building a git tree for
  63         performance testing. E.g., -j6 would be useful. Passed
  64         directly to make as "make $GIT_PERF_MAKE_OPTS".
  65
  66     GIT_PERF_MAKE_COMMAND
  67         An arbitrary command that'll be run in place of the make
  68         command, if set the GIT_PERF_MAKE_OPTS variable is
  69         ignored. Useful in cases where source tree changes might
  70         require issuing a different make command to different
  71         revisions.
  72
  73         This can be (ab)used to monkeypatch or otherwise change the
  74         tree about to be built. Note that the build directory can be
  75         re-used for subsequent runs so the make command might get
  76         executed multiple times on the same tree, but don't count on
  77         any of that, that's an implementation detail that might change
  78         in the future.
  79
  80     GIT_PERF_REPO
  81     GIT_PERF_LARGE_REPO
  82         Repositories to copy for the performance tests.  The normal
  83         repo should be at least git.git size.  The large repo should
  84         probably be about linux.git size for optimal results.
  85         Both default to the git.git you are running from.
  86
  87 You can also pass the options taken by ordinary git tests; the most
  88 useful one is:
  89
  90 --root=<directory>::
  91         Create "trash" directories used to store all temporary data during
  92         testing under <directory>, instead of the t/ directory.
  93         Using this option with a RAM-based filesystem (such as tmpfs)
  94         can massively speed up the test suite.
  95
  96
  97 Naming Tests
  98 ------------
  99
 100 The performance test files are named as:
 101
 102         pNNNN-commandname-details.sh
 103
 104 where N is a decimal digit.  The same conventions for choosing NNNN as
 105 for normal tests apply.
 106
 107
 108 Writing Tests
 109 -------------
 110
 111 The perf script starts much like a normal test script, except it
 112 sources perf-lib.sh:
 113
 114         #!/bin/sh
 115         #
 116         # Copyright (c) 2005 Junio C Hamano
 117         #
 118
 119         test_description='xxx performance test'
 120         . ./perf-lib.sh
 121
 122 After that you will want to use some of the following:
 123
 124         test_perf_fresh_repo    # sets up an empty repository
 125         test_perf_default_repo  # sets up a "normal" repository
 126         test_perf_large_repo    # sets up a "large" repository
 127
 128         test_perf_default_repo sub  # ditto, in a subdir "sub"
 129
 130         test_checkout_worktree  # if you need the worktree too
 131
 132 At least one of the first two is required!
 133
 134 You can use test_expect_success as usual. In both test_expect_success
 135 and in test_perf, running "git" points to the version that is being
 136 perf-tested. The $MODERN_GIT variable points to the git wrapper for the
 137 currently checked-out version (i.e., the one that matches the t/perf
 138 scripts you are running).  This is useful if your setup uses commands
 139 that only work with newer versions of git than what you might want to
 140 test (but obviously your new commands must still create a state that can
 141 be used by the older version of git you are testing).
 142
 143 For actual performance tests, use
 144
 145         test_perf 'descriptive string' '
 146                 command1 &&
 147                 command2
 148         '
 149
 150 test_perf spawns a subshell, for lack of better options.  This means
 151 that
 152
 153 * you _must_ export all variables that you need in the subshell
 154
 155 * you _must_ flag all variables that you want to persist from the
 156   subshell with 'test_export':
 157
 158         test_perf 'descriptive string' '
 159                 foo=$(git rev-parse HEAD) &&
 160                 test_export foo
 161         '
 162
 163   The so-exported variables are automatically marked for export in the
 164   shell executing the perf test.  For your convenience, test_export is
 165   the same as export in the main shell.
 166
 167   This feature relies on a bit of magic using 'set' and 'source'.
 168   While we have tried to make sure that it can cope with embedded
 169   whitespace and other special characters, it will not work with
 170   multi-line data.