| 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 | Output format is in seconds "Elapsed(User + System)" |
| 32 | |
| 33 | You can compare multiple repositories and even git revisions with the |
| 34 | 'run' script: |
| 35 | |
| 36 | $ ./run . origin/next /path/to/git-tree p0001-rev-list.sh |
| 37 | |
| 38 | where . stands for the current git tree. The full invocation is |
| 39 | |
| 40 | ./run [<revision|directory>...] [--] [<test-script>...] |
| 41 | |
| 42 | A '.' argument is implied if you do not pass any other |
| 43 | revisions/directories. |
| 44 | |
| 45 | You can also manually test this or another git build tree, and then |
| 46 | call the aggregation script to summarize the results: |
| 47 | |
| 48 | $ ./p0001-rev-list.sh |
| 49 | [...] |
| 50 | $ ./run /path/to/other/git -- ./p0001-rev-list.sh |
| 51 | [...] |
| 52 | $ ./aggregate.perl . /path/to/other/git ./p0001-rev-list.sh |
| 53 | |
| 54 | aggregate.perl has the same invocation as 'run', it just does not run |
| 55 | anything beforehand. |
| 56 | |
| 57 | You can set the following variables (also in your config.mak): |
| 58 | |
| 59 | GIT_PERF_REPEAT_COUNT |
| 60 | Number of times a test should be repeated for best-of-N |
| 61 | measurements. Defaults to 3. |
| 62 | |
| 63 | GIT_PERF_MAKE_OPTS |
| 64 | Options to use when automatically building a git tree for |
| 65 | performance testing. E.g., -j6 would be useful. Passed |
| 66 | directly to make as "make $GIT_PERF_MAKE_OPTS". |
| 67 | |
| 68 | GIT_PERF_MAKE_COMMAND |
| 69 | An arbitrary command that'll be run in place of the make |
| 70 | command, if set the GIT_PERF_MAKE_OPTS variable is |
| 71 | ignored. Useful in cases where source tree changes might |
| 72 | require issuing a different make command to different |
| 73 | revisions. |
| 74 | |
| 75 | This can be (ab)used to monkeypatch or otherwise change the |
| 76 | tree about to be built. Note that the build directory can be |
| 77 | re-used for subsequent runs so the make command might get |
| 78 | executed multiple times on the same tree, but don't count on |
| 79 | any of that, that's an implementation detail that might change |
| 80 | in the future. |
| 81 | |
| 82 | GIT_PERF_REPO |
| 83 | GIT_PERF_LARGE_REPO |
| 84 | Repositories to copy for the performance tests. The normal |
| 85 | repo should be at least git.git size. The large repo should |
| 86 | probably be about linux.git size for optimal results. |
| 87 | Both default to the git.git you are running from. |
| 88 | |
| 89 | GIT_PERF_EXTRA |
| 90 | Boolean to enable additional tests. Most test scripts are |
| 91 | written to detect regressions between two versions of Git, and |
| 92 | the output will compare timings for individual tests between |
| 93 | those versions. Some scripts have additional tests which are not |
| 94 | run by default, that show patterns within a single version of |
| 95 | Git (e.g., performance of index-pack as the number of threads |
| 96 | changes). These can be enabled with GIT_PERF_EXTRA. |
| 97 | |
| 98 | GIT_PERF_USE_SCALAR |
| 99 | Boolean indicating whether to register test repo(s) with Scalar |
| 100 | before executing tests. |
| 101 | |
| 102 | You can also pass the options taken by ordinary git tests; the most |
| 103 | useful one is: |
| 104 | |
| 105 | --root=<directory>:: |
| 106 | Create "trash" directories used to store all temporary data during |
| 107 | testing under <directory>, instead of the t/ directory. |
| 108 | Using this option with a RAM-based filesystem (such as tmpfs) |
| 109 | can massively speed up the test suite. |
| 110 | |
| 111 | |
| 112 | Naming Tests |
| 113 | ------------ |
| 114 | |
| 115 | The performance test files are named as: |
| 116 | |
| 117 | pNNNN-commandname-details.sh |
| 118 | |
| 119 | where N is a decimal digit. The same conventions for choosing NNNN as |
| 120 | for normal tests apply. |
| 121 | |
| 122 | |
| 123 | Writing Tests |
| 124 | ------------- |
| 125 | |
| 126 | The perf script starts much like a normal test script, except it |
| 127 | sources perf-lib.sh: |
| 128 | |
| 129 | #!/bin/sh |
| 130 | # |
| 131 | # Copyright (c) 2005 Junio C Hamano |
| 132 | # |
| 133 | |
| 134 | test_description='xxx performance test' |
| 135 | . ./perf-lib.sh |
| 136 | |
| 137 | After that you will want to use some of the following: |
| 138 | |
| 139 | test_perf_fresh_repo # sets up an empty repository |
| 140 | test_perf_default_repo # sets up a "normal" repository |
| 141 | test_perf_large_repo # sets up a "large" repository |
| 142 | |
| 143 | test_perf_default_repo sub # ditto, in a subdir "sub" |
| 144 | |
| 145 | test_checkout_worktree # if you need the worktree too |
| 146 | |
| 147 | At least one of the first two is required! |
| 148 | |
| 149 | You can use test_expect_success as usual. In both test_expect_success |
| 150 | and in test_perf, running "git" points to the version that is being |
| 151 | perf-tested. The $MODERN_GIT variable points to the git wrapper for the |
| 152 | currently checked-out version (i.e., the one that matches the t/perf |
| 153 | scripts you are running). This is useful if your setup uses commands |
| 154 | that only work with newer versions of git than what you might want to |
| 155 | test (but obviously your new commands must still create a state that can |
| 156 | be used by the older version of git you are testing). |
| 157 | |
| 158 | For actual performance tests, use |
| 159 | |
| 160 | test_perf 'descriptive string' ' |
| 161 | command1 && |
| 162 | command2 |
| 163 | ' |
| 164 | |
| 165 | test_perf spawns a subshell, for lack of better options. This means |
| 166 | that |
| 167 | |
| 168 | * you _must_ export all variables that you need in the subshell |
| 169 | |
| 170 | * you _must_ flag all variables that you want to persist from the |
| 171 | subshell with 'test_export': |
| 172 | |
| 173 | test_perf 'descriptive string' ' |
| 174 | foo=$(git rev-parse HEAD) && |
| 175 | test_export foo |
| 176 | ' |
| 177 | |
| 178 | The so-exported variables are automatically marked for export in the |
| 179 | shell executing the perf test. For your convenience, test_export is |
| 180 | the same as export in the main shell. |
| 181 | |
| 182 | This feature relies on a bit of magic using 'set' and 'source'. |
| 183 | While we have tried to make sure that it can cope with embedded |
| 184 | whitespace and other special characters, it will not work with |
| 185 | multi-line data. |
| 186 | |
| 187 | Rather than tracking the performance by run-time as `test_perf` does, you |
| 188 | may also track output size by using `test_size`. The stdout of the |
| 189 | function should be a single numeric value, which will be captured and |
| 190 | shown in the aggregated output. For example: |
| 191 | |
| 192 | test_perf 'time foo' ' |
| 193 | ./foo >foo.out |
| 194 | ' |
| 195 | |
| 196 | test_size 'output size' |
| 197 | wc -c <foo.out |
| 198 | ' |
| 199 | |
| 200 | might produce output like: |
| 201 | |
| 202 | Test origin HEAD |
| 203 | ------------------------------------------------------------- |
| 204 | 1234.1 time foo 0.37(0.79+0.02) 0.26(0.51+0.02) -29.7% |
| 205 | 1234.2 output size 4.3M 3.6M -14.7% |
| 206 | |
| 207 | The item being measured (and its units) is up to the test; the context |
| 208 | and the test title should make it clear to the user whether bigger or |
| 209 | smaller numbers are better. Unlike test_perf, the test code will only be |
| 210 | run once, since output sizes tend to be more deterministic than timings. |