fetch: speed up mirror-fetches with many refs

Hi,

this is the third version of my patch series which aimn to speed up mirror-fetches in repos with huge amounts of refs. Again, the only change compared to v2 is a change in commit messages: Chris has rightly pointed out that the benchmarks were a bit confusing, so I've updated them to hopefully be less so.

Thanks for your feedback!

Patrick

Patrick Steinhardt (2):
fetch-pack: use commit-graph when computing cutoff
fetch: skip computing output width when not printing anything

 builtin/fetch.c |  8 ++++++--
 fetch-pack.c    | 28 ++++++++++++++++------------
 2 files changed, 22 insertions(+), 14 deletions(-)

Range-diff against v2:
1: 6fac914f0f ! 1: 077d06764c fetch-pack: use commit-graph when computing cutoff
@@ Commit message
the commit-graph first, which is a lot more efficient.

Benchmarks in a repository with about 2,1 million refs and an up-to-date
- commit-graph show a 20% speedup when mirror-fetching:
+ commit-graph show an almost 20% speedup when mirror-fetching:

- Benchmark 1: git fetch --atomic +refs/*:refs/* (v2.35.0)
- Time (mean ± σ): 75.264 s ± 1.115 s [User: 68.199 s, System: 10.094 s]
- Range (min … max): 74.145 s … 76.862 s 5 runs
+ Benchmark 1: git fetch +refs/*:refs/* (v2.35.0)
+ Time (mean ± σ): 115.587 s ± 2.009 s [User: 109.874 s, System: 11.305 s]
+ Range (min … max): 113.584 s … 118.820 s 5 runs

- Benchmark 2: git fetch --atomic +refs/*:refs/* (HEAD)
- Time (mean ± σ): 62.350 s ± 0.854 s [User: 55.412 s, System: 9.976 s]
- Range (min … max): 61.224 s … 63.216 s 5 runs
+ Benchmark 2: git fetch +refs/*:refs/* (HEAD)
+ Time (mean ± σ): 96.859 s ± 0.624 s [User: 91.948 s, System: 10.980 s]
+ Range (min … max): 96.180 s … 97.875 s 5 runs

Summary
- 'git fetch --atomic +refs/*:refs/* (HEAD)' ran
- 1.21 ± 0.02 times faster than 'git fetch --atomic +refs/*:refs/* (v2.35.0)'
+ 'git fetch +refs/*:refs/* (HEAD)' ran
+ 1.19 ± 0.02 times faster than 'git fetch +refs/*:refs/* (v2.35.0)'

2: 4b9bbcf795 ! 2: ef1fd07be5 fetch: skip computing output width when not printing anything
@@ Commit message
don't print the summary, but still compute the length.

Skip computing the summary width when the user asked for us to be quiet.
- This gives us a small speedup of nearly 10% when doing a dry-run
- mirror-fetch in a repository with thousands of references being updated:
+ This gives us a speedup of nearly 10% when doing a mirror-fetch in a
+ repository with thousands of references being updated:

- Benchmark 1: git fetch --prune --dry-run +refs/*:refs/* (HEAD~)
- Time (mean ± σ): 34.048 s ± 0.233 s [User: 30.739 s, System: 4.640 s]
- Range (min … max): 33.785 s … 34.296 s 5 runs
+ Benchmark 1: git fetch --quiet +refs/*:refs/* (HEAD~)
+ Time (mean ± σ): 96.078 s ± 0.508 s [User: 91.378 s, System: 10.870 s]
+ Range (min … max): 95.449 s … 96.760 s 5 runs

- Benchmark 2: git fetch --prune --dry-run +refs/*:refs/* (HEAD)
- Time (mean ± σ): 30.768 s ± 0.287 s [User: 27.534 s, System: 4.565 s]
- Range (min … max): 30.432 s … 31.181 s 5 runs
+ Benchmark 2: git fetch --quiet +refs/*:refs/* (HEAD)
+ Time (mean ± σ): 88.214 s ± 0.192 s [User: 83.274 s, System: 10.978 s]
+ Range (min … max): 87.998 s … 88.446 s 5 runs

Summary
- 'git fetch --prune --dry-run +refs/*:refs/* (HEAD)' ran
- 1.11 ± 0.01 times faster than 'git fetch --prune --dry-run +refs/*:refs/* (HEAD~)'
+ 'git fetch --quiet +refs/*:refs/* (HEAD)' ran
+ 1.09 ± 0.01 times faster than 'git fetch --quiet +refs/*:refs/* (HEAD~)'

2.35.1