[PATCH 1/8] tree-walk: report recursion counts

["Derrick Stolee via GitGitGadget" <gitgitgadget@xxxxxxxxx>]

From: Derrick Stolee <dstolee@xxxxxxxxxxxxx>

The traverse_trees() method recusively walks through trees, but also
prunes the tree-walk based on a callback. Some callers, such as
unpack_trees(), are quite complicated and can have wildly different
performance between two different commands.

Create constants that count these values and then report the results at
the end of a process. These counts are cumulative across multiple "root"
instances of traverse_trees(), but they provide reproducible values for
demonstrating improvements to the pruning algorithm when possible.

Signed-off-by: Derrick Stolee <dstolee@xxxxxxxxxxxxx>
---
 tree-walk.c    | 33 +++++++++++++++++++++++++++++++++
 unpack-trees.c |  1 -
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/tree-walk.c b/tree-walk.c
index 0160294712b..2d6226d5f18 100644
--- a/tree-walk.c
+++ b/tree-walk.c
@@ -4,6 +4,7 @@
 #include "object-store.h"
 #include "tree.h"
 #include "pathspec.h"
+#include "json-writer.h"
 
 static const char *get_mode(const char *str, unsigned int *modep)
 {
@@ -167,6 +168,25 @@ int tree_entry_gently(struct tree_desc *desc, struct name_entry *entry)
 	return 1;
 }
 
+static int traverse_trees_atexit_registered;
+static int traverse_trees_count;
+static int traverse_trees_cur_depth;
+static int traverse_trees_max_depth;
+
+static void trace2_traverse_trees_statistics_atexit(void)
+{
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	jw_object_intmax(&jw, "traverse_trees_count", traverse_trees_count);
+	jw_object_intmax(&jw, "traverse_trees_max_depth", traverse_trees_max_depth);
+	jw_end(&jw);
+
+	trace2_data_json("traverse_trees", the_repository, "statistics", &jw);
+
+	jw_release(&jw);
+}
+
 void setup_traverse_info(struct traverse_info *info, const char *base)
 {
 	size_t pathlen = strlen(base);
@@ -180,6 +200,11 @@ void setup_traverse_info(struct traverse_info *info, const char *base)
 	info->namelen = pathlen;
 	if (pathlen)
 		info->prev = &dummy;
+
+	if (trace2_is_enabled() && !traverse_trees_atexit_registered) {
+		atexit(trace2_traverse_trees_statistics_atexit);
+		traverse_trees_atexit_registered = 1;
+	}
 }
 
 char *make_traverse_path(char *path, size_t pathlen,
@@ -416,6 +441,12 @@ int traverse_trees(struct index_state *istate,
 	int interesting = 1;
 	char *traverse_path;
 
+	traverse_trees_count++;
+	traverse_trees_cur_depth++;
+
+	if (traverse_trees_cur_depth > traverse_trees_max_depth)
+		traverse_trees_max_depth = traverse_trees_cur_depth;
+
 	if (n >= ARRAY_SIZE(entry))
 		BUG("traverse_trees() called with too many trees (%d)", n);
 
@@ -515,6 +546,8 @@ int traverse_trees(struct index_state *istate,
 	free(traverse_path);
 	info->traverse_path = NULL;
 	strbuf_release(&base);
+
+	traverse_trees_cur_depth--;
 	return error;
 }
 
diff --git a/unpack-trees.c b/unpack-trees.c
index 323280dd48b..02f484604ac 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -1559,7 +1559,6 @@ static void populate_from_existing_patterns(struct unpack_trees_options *o,
 	free(sparse);
 }
 
-
 static int verify_absent(const struct cache_entry *,
 			 enum unpack_trees_error_types,
 			 struct unpack_trees_options *);
-- 
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