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83 lines
2.9 KiB
Markdown
83 lines
2.9 KiB
Markdown
# Building and Running
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Benchmarks are implemented using [Google Benchmark](https://github.com/google/benchmark).
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To build the benchmarks in this directory you need to set the benchmark
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option while configuring the build with meson:
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```
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meson build -Dbenchmark=enabled --buildtype=debugoptimized
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```
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The default build type is `debugoptimized`, which is good enough for
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benchmarking, but you can also get the fastest mode with `release`
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build type:
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```
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meson build -Dbenchmark=enabled --buildtype=release
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```
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You should, of course, enable features you want to benchmark, like
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`-Dfreetype`, `-Dfontations`, `-Dcoretext`, etc.
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Then build a specific benchmark binaries with ninja, eg.:
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```
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ninja -Cbuild perf/benchmark-set
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```
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or just build the whole project:
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```
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ninja -Cbuild
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```
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Finally, to run one of the benchmarks:
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```
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./build/perf/benchmark-set
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```
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It's possible to filter the benchmarks being run and customize the output
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via flags to the benchmark binary. See the
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[Google Benchmark User Guide](https://github.com/google/benchmark/blob/main/docs/user_guide.md#user-guide) for more details.
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The most useful benchmark is `benchmark-font`. You can provide custom fonts to it too.
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For example, to run only the "paint" benchmarks, against a given font, you can do:
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```
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./build/perf/benchmark-font NotoColorEmoji-Regular.ttf --benchmark_filter="paint"
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```
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Some useful options are: `--benchmark_repetitions=5` to run the benchmark 5 times,
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`--benchmark_min_time=.1s` to run the benchmark for at least .1 seconds (defaults
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to .5s), and `--benchmark_filter=...` to filter the benchmarks by regular expression.
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To compare before/after benchmarks, you need to save the benchmark results in files
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for both runs. Use `--benchmark_out=results.json` to output the results in JSON format.
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Then you can use:
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```
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./subprojects/benchmark-1.8.4/tools/compare.py benchmarks before.json after.json
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```
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Substitute your version of benchmark instead of 1.8.4.
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# Profiling
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If you like to disable optimizations and enable frame pointers for better profiling output,
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you can do so with the following meson command:
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```
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CXXFLAGS="-fno-omit-frame-pointer" meson --reconfigure build -Dbenchmark=enabled --buildtype=debug
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ninja -Cbuild
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```
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However, this will slow down the benchmarks significantly and might give you inaccurate
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information as to where to optimize. It's better to profile the `debugoptimized` build (the default).
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Then run the benchmark with perf:
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```
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perf record -g build/perf/benchmark-subset --benchmark_filter="BM_subset_codepoints/subset_notocjk/100000" --benchmark_repetitions=5
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```
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You probably want to filter to a specific benchmark of interest and set the number of
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repititions high enough to get a good sampling of profile data.
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Finally view the profile with:
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```
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perf report
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```
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Another useful `perf` tool is the `perf stat` command, which can give you a quick overview
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of the performance of a benchmark, as well as stalled cycles, cache misses, and mispredicted branches.
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