From: Derrick Stolee <dstolee@xxxxxxxxxxxxx>
The previous change reduced time spent in strlen() while comparing
consecutive paths in verify_cache(), but we can do better. The
conditional checks the existence of a directory separator at the correct
location, but only after doing a string comparison. Swap the order to be
logically equivalent but perform fewer string comparisons.
To test the effect on performance, I used a repository with over three
million paths in the index. I then ran the following command on repeat:
git -c index.threads=1 commit --amend --allow-empty --no-edit
Here are the measurements over 10 runs after a 5-run warmup:
Benchmark #1: v2.30.0
Time (mean ± σ): 854.5 ms ± 18.2 ms
Range (min … max): 825.0 ms … 892.8 ms
Benchmark #2: Previous change
Time (mean ± σ): 833.2 ms ± 10.3 ms
Range (min … max): 815.8 ms … 849.7 ms
Benchmark #3: This change
Time (mean ± σ): 815.5 ms ± 18.1 ms
Range (min … max): 795.4 ms … 849.5 ms
This change is 2% faster than the previous change and 5% faster than
v2.30.0.
Signed-off-by: Derrick Stolee <dstolee@xxxxxxxxxxxxx>
---
cache-tree.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/cache-tree.c b/cache-tree.c
index 4274de75bac..3f1a8d4f1b7 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -191,8 +191,8 @@ static int verify_cache(struct cache_entry **cache,
const char *next_name = next_ce->name;
int this_len = ce_namelen(this_ce);
if (this_len < ce_namelen(next_ce) &&
- strncmp(this_name, next_name, this_len) == 0 &&
- next_name[this_len] == '/') {
+ next_name[this_len] == '/' &&
+ strncmp(this_name, next_name, this_len) == 0) {
if (10 < ++funny) {
fprintf(stderr, "...\n");
break;
--
gitgitgadget
