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

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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>
This commit is contained in:
Tian Yuchen
2026-01-31 01:01:23 +08:00
committed by Junio C Hamano
parent ea717645d1
commit 8466efa4bd
1 changed files with 38 additions and 15 deletions
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53
t/perf/p3400-rebase.sh
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@@ -9,21 +9,44 @@ test_expect_success 'setup rebasing on top of a lot of changes' '
git checkout -f -B base &&
git checkout -B to-rebase &&
git checkout -B upstream &&
for i in $(test_seq 100)
do
# simulate huge diffs
echo change$i >unrelated-file$i &&
test_seq 1000 >>unrelated-file$i &&
git add unrelated-file$i &&
test_tick &&
git commit -m commit$i unrelated-file$i &&
echo change$i >unrelated-file$i &&
test_seq 1000 | sort -nr >>unrelated-file$i &&
git add unrelated-file$i &&
test_tick &&
git commit -m commit$i-reverse unrelated-file$i ||
return 1
done &&
test_seq 1000 >content_fwd &&
sort -nr content_fwd >content_rev &&
(
for i in $(test_seq 100)
do
test_tick &&
echo "commit refs/heads/upstream" &&
echo "committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE" &&
echo "data <<EOF" &&
echo "commit$i" &&
echo "EOF" &&
if test "$i" = 1; then
echo "from refs/heads/upstream^0"
fi &&
echo "M 100644 inline unrelated-file$i" &&
echo "data <<EOF" &&
echo "change$i" &&
cat content_fwd &&
echo "EOF" &&
echo "commit refs/heads/upstream" &&
echo "committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE" &&
echo "data <<EOF" &&
echo "commit$i-reverse" &&
echo "EOF" &&
echo "M 100644 inline unrelated-file$i" &&
echo "data <<EOF" &&
echo "change$i" &&
cat content_rev &&
echo "EOF" || exit 1
done
) >fast_import_stream &&
git fast-import <fast_import_stream &&
git repack -a -d &&
git checkout -f upstream &&
git checkout to-rebase &&
test_commit our-patch interesting-file
'