sparse-index: count lstat() calls

The clear_skip_worktree.. methods already report some statistics about
how many cache entries are checked against path_found() due to having
the skip-worktree bit set. However, due to path_found() performing some
caching, this isn't the only information that would be helpful to
report.

Add a new lstat_count member to the path_found_data struct to count the
number of times path_found() calls lstat(). This will be helpful to help
explain performance problems in this method as well as to demonstrate
future changes to the caching algorithm in a more concrete way than
end-to-end timings.

Signed-off-by: Derrick Stolee <[email protected]>
Reviewed-by: Elijah Newren <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: derrickstolee

sparse-index.c

@@ -442,6 +442,7 @@ void ensure_correct_sparsity(struct index_state *istate)
 struct path_found_data {
 	struct strbuf dir;
 	int dir_found;
+	size_t lstat_count;
 };
 
 #define PATH_FOUND_DATA_INIT { \
@@ -469,6 +470,7 @@ static int path_found(const char *path, struct path_found_data *data)
 	/*
 	 * If path itself exists, return 1.
 	 */
+	data->lstat_count++;
 	if (!lstat(path, &st))
 		return 1;
 
@@ -493,6 +495,7 @@ static int path_found(const char *path, struct path_found_data *data)
 	strbuf_reset(&data->dir);
 	strbuf_add(&data->dir, path, newdir - path + 1);
 
+	data->lstat_count++;
 	data->dir_found = !lstat(data->dir.buf, &st);
 
 	return 0;
@@ -524,6 +527,8 @@ static int clear_skip_worktree_from_present_files_sparse(struct index_state *ist
 
 	trace2_data_intmax("index", istate->repo,
 			   "sparse_path_count", path_count);
+	trace2_data_intmax("index", istate->repo,
+			   "sparse_lstat_count", data.lstat_count);
 	trace2_region_leave("index", "clear_skip_worktree_from_present_files_sparse",
 			    istate->repo);
 	clear_path_found_data(&data);
@@ -553,6 +558,8 @@ static void clear_skip_worktree_from_present_files_full(struct index_state *ista
 
 	trace2_data_intmax("index", istate->repo,
 			   "full_path_count", path_count);
+	trace2_data_intmax("index", istate->repo,
+			   "full_lstat_count", data.lstat_count);
 	trace2_region_leave("index", "clear_skip_worktree_from_present_files_full",
 			    istate->repo);
 	clear_path_found_data(&data);