@matheusbsbs / matheus-bagliano / commits / 8466efa4bd

t/perf/p3400: speed up setup using fast-import

The setup phase in 't/perf/p3400-rebase.sh' generates 100 commits to simulate a noisy history. It currently uses a shell loop that invokes 'git add', 'git commit', 'test_seq', and 'sort' in each iteration. This incurs significant overhead due to repeated process spawning. Optimize the setup by using 'git fast-import' to generate the commit history. Additionally, pre-compute the forward and reversed file contents to avoid repetitive execution of 'seq' and 'sort'. To ensure the test measures rebase performance against a consistent object layout (rather than the suboptimal pack/loose objects created by the raw import), perform a full repack (`git repack -a -d`) at the end of the setup. This reduces the setup time significantly while maintaining the validity of the subsequent performance tests. Performance enhancement (Average value of 5 tests): Real Rebase Before: 29.045s 13.34s After: 21.989s 12.84s Measured on Lenovo Yoga 2020, Ubuntu 24.04. Signed-off-by: Tian Yuchen <a3205153416@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Tian Yuchen committed Jan 31, 2026 at 01:01 UTC 8466efa4bd92b970f7a37159404aef33296d9d46
1 file changed +38 -15
t/perf/p3400-rebase.sh
+38 -15
@@ -9,21 +9,44 @@ test_expect_success 'setup rebasing on top of a lot of changes' '
9 git checkout -f -B base &&
10 git checkout -B to-rebase &&
11 git checkout -B upstream &&
12 - for i in $(test_seq 100)
13 - do
14 - # simulate huge diffs
15 - echo change$i >unrelated-file$i &&
16 - test_seq 1000 >>unrelated-file$i &&
17 - git add unrelated-file$i &&
18 - test_tick &&
19 - git commit -m commit$i unrelated-file$i &&
20 - echo change$i >unrelated-file$i &&
21 - test_seq 1000 | sort -nr >>unrelated-file$i &&
22 - git add unrelated-file$i &&
23 - test_tick &&
24 - git commit -m commit$i-reverse unrelated-file$i ||
25 - return 1
26 - done &&
12 + test_seq 1000 >content_fwd &&
13 + sort -nr content_fwd >content_rev &&
14 + (
15 + for i in $(test_seq 100)
16 + do
17 + test_tick &&
18 + echo "commit refs/heads/upstream" &&
19 + echo "committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE" &&
20 + echo "data <<EOF" &&
21 + echo "commit$i" &&
22 + echo "EOF" &&
23 +
24 + if test "$i" = 1; then
25 + echo "from refs/heads/upstream^0"
26 + fi &&
27 +
28 + echo "M 100644 inline unrelated-file$i" &&
29 + echo "data <<EOF" &&
30 + echo "change$i" &&
31 + cat content_fwd &&
32 + echo "EOF" &&
33 +
34 + echo "commit refs/heads/upstream" &&
35 + echo "committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE" &&
36 + echo "data <<EOF" &&
37 + echo "commit$i-reverse" &&
38 + echo "EOF" &&
39 + echo "M 100644 inline unrelated-file$i" &&
40 + echo "data <<EOF" &&
41 + echo "change$i" &&
42 + cat content_rev &&
43 + echo "EOF" || exit 1
44 + done
45 + ) >fast_import_stream &&
46 +
47 + git fast-import <fast_import_stream &&
48 + git repack -a -d &&
49 + git checkout -f upstream &&
50 git checkout to-rebase &&
51 test_commit our-patch interesting-file
52 '