Am Sun, Jul 02, 2023 at 06:02:43PM -0400 schrieb Jeff King: > On Sun, Jul 02, 2023 at 08:56:11AM -0400, Jeff King wrote: > > > My biggest question would be whether this introduces any performance > > penalty for the more common cases (lightweight tags and single-level > > annotated tags). The answer is "no", I think; we are already paying the > > cost to parse every object to find out if it's a tag, and your new loop > > only does an extra parse if we see a tag-of-tag. Good. > > Reading more carefully, I think this does actually change the > performance a bit, because we end up parsing the pointed-to commits, as > well. So here's before and after your patch running "git for-each-ref > --points-at=HEAD" on linux.git (785 refs, all but 3 are tags): > > Benchmark 1: ./git.old for-each-ref --points-at=HEAD > Time (mean ± σ): 11.4 ms ± 0.2 ms [User: 6.5 ms, System: 4.9 ms] > Range (min … max): 11.0 ms … 12.3 ms 239 runs > > Benchmark 2: ./git.new for-each-ref --points-at=HEAD > Time (mean ± σ): 20.6 ms ± 0.5 ms [User: 10.4 ms, System: 10.2 ms] > Range (min … max): 19.8 ms … 22.7 ms 133 runs > > Summary > './git.old for-each-ref --points-at=HEAD' ran > 1.80 ± 0.06 times faster than './git.new for-each-ref --points-at=HEAD' > > The absolute numbers are pretty small, but the percent change isn't > great. I'll send some patches in a minute that can be applied on top to > improve this case, as well as fix the other issues I pointed out in the > existing code. I have to admit I was not entirely sure about the performance implications. The relative performance drop is indeed substantial. Thanks for the thorough review and swiftly taking care of these! -- Jan
