On Mon, Jun 26, 2023 at 03:09:57PM +0000, Derrick Stolee via GitGitGadget wrote:
> +for pattern in "refs/heads/" "refs/tags/" "refs/remotes"
> +do
> + test_perf "count $pattern: git for-each-ref | wc -l" "
> + git for-each-ref $pattern | wc -l
> + "
> +
> + test_perf "count $pattern: git for-each-ref --count-match" "
> + git for-each-ref --count-matches $pattern
> + "
> +done
I don't think this is a very realistic perf test, because for-each-ref
is doing a bunch of work to generate its default format, only to have
"wc" throw most of it away. Doing:
git for-each-ref --format='%(refname)' | wc -l
is much better (obviously you have to remember to do that if you care
about optimizing your command, but that's true of --count-matches, too).
Running hyperfine with three variants shows that the command above is
competitive with --count-matches, though slightly slower (hyperfine
complains about short commands and outliers because these runtimes are
so tiny in the first place; I omitted those warnings from the output
below for readability):
Benchmark 1: ./git-for-each-ref refs/remotes/ | wc -l
Time (mean ± σ): 6.1 ms ± 0.2 ms [User: 3.0 ms, System: 3.6 ms]
Range (min … max): 5.6 ms … 7.1 ms 397 runs
Benchmark 2: ./git-for-each-ref --format="%(refname)" refs/remotes/ | wc -l
Time (mean ± σ): 3.3 ms ± 0.2 ms [User: 2.2 ms, System: 1.5 ms]
Range (min … max): 3.0 ms … 4.0 ms 774 runs
Benchmark 3: ./git-for-each-ref --count-matches refs/remotes/
Time (mean ± σ): 2.4 ms ± 0.1 ms [User: 1.5 ms, System: 0.9 ms]
Range (min … max): 2.2 ms … 3.4 ms 1018 runs
Summary
'./git-for-each-ref --count-matches refs/remotes/' ran
1.33 ± 0.10 times faster than './git-for-each-ref --format="%(refname)" refs/remotes/ | wc -l'
2.48 ± 0.17 times faster than './git-for-each-ref refs/remotes/ | wc -l'
I will note this is an unloaded multi-core system, which gives the piped
version a slight edge. Total CPU is probably more interesting than
wall-clock time, but all of these are so short that I think the results
should be taken with a pretty big grain of salt (I had to switch from
the "powersave" to "performance" CPU governor just to get more
consistent results).
-Peff
