mirror of
https://github.com/uutils/coreutils
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47 lines
1.7 KiB
Markdown
47 lines
1.7 KiB
Markdown
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## Benchmarking cut
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### Performance profile
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In normal use cases a significant amount of the total execution time of `cut`
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is spent performing I/O. When invoked with the `-f` option (cut fields) some
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CPU time is spent on detecting fields (in `Searcher::next`). Other than that
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some small amount of CPU time is spent on breaking the input stream into lines.
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### How to
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When fixing bugs or adding features you might want to compare
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performance before and after your code changes.
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- `hyperfine` can be used to accurately measure and compare the total
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execution time of one or more commands.
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```
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$ cargo build --release --package uu_cut
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$ hyperfine -w3 "./target/release/cut -f2-4,8 -d' ' input.txt" "cut -f2-4,8 -d' ' input.txt"
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```
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You can put those two commands in a shell script to be sure that you don't
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forget to build after making any changes.
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When optimizing or fixing performance regressions seeing the number of times a
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function is called, and the amount of time it takes can be useful.
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- `cargo flamegraph` generates flame graphs from function level metrics it records using `perf` or `dtrace`
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```
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$ cargo flamegraph --bin cut --package uu_cut -- -f1,3-4 input.txt > /dev/null
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```
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### What to benchmark
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There are four different performance paths in `cut` to benchmark.
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- Byte ranges `-c`/`--characters` or `-b`/`--bytes` e.g. `cut -c 2,4,6-`
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- Byte ranges with output delimiters e.g. `cut -c 4- --output-delimiter=/`
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- Fields e.g. `cut -f -4`
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- Fields with output delimiters e.g. `cut -f 7-10 --output-delimiter=:`
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Choose a test input file with large number of lines so that program startup time does not significantly affect the benchmark.
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