unpack-trees.c: add performance tracing

We're going to optimize unpack_trees() a bit in the following
patches. Let's add some tracing to measure how long it takes before
and after. This is the baseline ("git checkout -" on gcc.git, 80k
files on worktree)

    0.018239226 s: read cache .git/index
    0.052541655 s: preload index
    0.001537598 s: refresh index
    0.168167768 s: unpack trees
    0.002897186 s: update worktree after a merge
    0.131661745 s: repair cache-tree
    0.075389117 s: write index, changed mask = 2a
    0.111702023 s: unpack trees
    0.000023245 s: update worktree after a merge
    0.111793866 s: diff-index
    0.587933288 s: git command: /home/pclouds/w/git/git checkout -

Signed-off-by: Nguyễn Thái Ngọc Duy <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pclouds

cache-tree.c

@@ -426,6 +426,7 @@ static int update_one(struct cache_tree *it,
 
 int cache_tree_update(struct index_state *istate, int flags)
 {
+	uint64_t start = getnanotime();
 	struct cache_tree *it = istate->cache_tree;
 	struct cache_entry **cache = istate->cache;
 	int entries = istate->cache_nr;
@@ -437,6 +438,7 @@ int cache_tree_update(struct index_state *istate, int flags)
 	if (i < 0)
 		return i;
 	istate->cache_changed |= CACHE_TREE_CHANGED;
+	trace_performance_since(start, "repair cache-tree");
 	return 0;
 }
 

unpack-trees.c

@@ -352,6 +352,7 @@ static int check_updates(struct unpack_trees_options *o)
 	struct progress *progress = NULL;
 	struct index_state *index = &o->result;
 	struct checkout state = CHECKOUT_INIT;
+	uint64_t start = getnanotime();
 	int i;
 
 	state.force = 1;
@@ -423,6 +424,7 @@ static int check_updates(struct unpack_trees_options *o)
 	errs |= finish_delayed_checkout(&state);
 	if (o->update)
 		git_attr_set_direction(GIT_ATTR_CHECKIN, NULL);
+	trace_performance_since(start, "update worktree after a merge");
 	return errs != 0;
 }
 
@@ -1275,6 +1277,7 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 	int i, ret;
 	static struct cache_entry *dfc;
 	struct exclude_list el;
+	uint64_t start = getnanotime();
 
 	if (len > MAX_UNPACK_TREES)
 		die("unpack_trees takes at most %d trees", MAX_UNPACK_TREES);
@@ -1423,6 +1426,7 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 			goto done;
 		}
 	}
+	trace_performance_since(start, "unpack trees");
 
 	ret = check_updates(o) ? (-2) : 0;
 	if (o->dst_index) {