[PATCH] trace: measure where the time is spent in the index-heavy operations

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

All the known heavy code blocks are measured (except object database
access). This should help identify if an optimization is effective or
not. An unoptimized git-status would give something like below (92% of
time is accounted).

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 This was in my old index-helper series. The series was replaced by
 fsmonitor but perhaps some measurements like this still helps.

 In my old version I measured packed-refs read time too. But
 packed-refs is mmap'd now, no need to worry about it (or at least its
 initial cost).

 diff-lib.c      |  4 ++++
 dir.c           |  2 ++
 name-hash.c     |  3 +++
 preload-index.c |  2 ++
 read-cache.c    | 11 +++++++++++
 5 files changed, 22 insertions(+)

diff --git a/diff-lib.c b/diff-lib.c
index 8104603a3b..a228e1a219 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -92,6 +92,7 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 	int diff_unmerged_stage = revs->max_count;
 	unsigned ce_option = ((option & DIFF_RACY_IS_MODIFIED)
 			      ? CE_MATCH_RACY_IS_DIRTY : 0);
+	uint64_t start = getnanotime();
 
 	diff_set_mnemonic_prefix(&revs->diffopt, "i/", "w/");
 
@@ -246,6 +247,7 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 	}
 	diffcore_std(&revs->diffopt);
 	diff_flush(&revs->diffopt);
+	trace_performance_since(start, "diff-files");
 	return 0;
 }
 
@@ -512,6 +514,7 @@ static int diff_cache(struct rev_info *revs,
 int run_diff_index(struct rev_info *revs, int cached)
 {
 	struct object_array_entry *ent;
+	uint64_t start = getnanotime();
 
 	ent = revs->pending.objects;
 	if (diff_cache(revs, &ent->item->oid, ent->name, cached))
@@ -521,6 +524,7 @@ int run_diff_index(struct rev_info *revs, int cached)
 	diffcore_fix_diff_index(&revs->diffopt);
 	diffcore_std(&revs->diffopt);
 	diff_flush(&revs->diffopt);
+	trace_performance_since(start, "diff-index");
 	return 0;
 }
 
diff --git a/dir.c b/dir.c
index 7c4b45e30e..4479a02a49 100644
--- a/dir.c
+++ b/dir.c
@@ -2248,6 +2248,7 @@ int read_directory(struct dir_struct *dir, struct index_state *istate,
 		   const char *path, int len, const struct pathspec *pathspec)
 {
 	struct untracked_cache_dir *untracked;
+	uint64_t start = getnanotime();
 
 	if (has_symlink_leading_path(path, len))
 		return dir->nr;
@@ -2286,6 +2287,7 @@ int read_directory(struct dir_struct *dir, struct index_state *istate,
 		dir->nr = i;
 	}
 
+	trace_performance_since(start, "read directory %.*s", len, path);
 	if (dir->untracked) {
 		static struct trace_key trace_untracked_stats = TRACE_KEY_INIT(UNTRACKED_STATS);
 		trace_printf_key(&trace_untracked_stats,
diff --git a/name-hash.c b/name-hash.c
index 45c98db0a0..ada66f066a 100644
--- a/name-hash.c
+++ b/name-hash.c
@@ -578,6 +578,8 @@ static void threaded_lazy_init_name_hash(
 
 static void lazy_init_name_hash(struct index_state *istate)
 {
+	uint64_t start = getnanotime();
+
 	if (istate->name_hash_initialized)
 		return;
 	hashmap_init(&istate->name_hash, cache_entry_cmp, NULL, istate->cache_nr);
@@ -600,6 +602,7 @@ static void lazy_init_name_hash(struct index_state *istate)
 	}
 
 	istate->name_hash_initialized = 1;
+	trace_performance_since(start, "initialize name hash");
 }
 
 /*
diff --git a/preload-index.c b/preload-index.c
index 2a83255e4e..4d08d44874 100644
--- a/preload-index.c
+++ b/preload-index.c
@@ -78,6 +78,7 @@ static void preload_index(struct index_state *index,
 {
 	int threads, i, work, offset;
 	struct thread_data data[MAX_PARALLEL];
+	uint64_t start = getnanotime();
 
 	if (!core_preload_index)
 		return;
@@ -108,6 +109,7 @@ static void preload_index(struct index_state *index,
 		if (pthread_join(p->pthread, NULL))
 			die("unable to join threaded lstat");
 	}
+	trace_performance_since(start, "preload index");
 }
 #endif
 
diff --git a/read-cache.c b/read-cache.c
index 2eb81a66b9..1f00aee6a2 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1372,6 +1372,7 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 	const char *typechange_fmt;
 	const char *added_fmt;
 	const char *unmerged_fmt;
+	uint64_t start = getnanotime();
 
 	modified_fmt = (in_porcelain ? "M\t%s\n" : "%s: needs update\n");
 	deleted_fmt = (in_porcelain ? "D\t%s\n" : "%s: needs update\n");
@@ -1442,6 +1443,7 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 
 		replace_index_entry(istate, i, new);
 	}
+	trace_performance_since(start, "refresh index");
 	return has_errors;
 }
 
@@ -1877,12 +1879,15 @@ int read_index_from(struct index_state *istate, const char *path)
 	int ret;
 	char *base_sha1_hex;
 	const char *base_path;
+	uint64_t start;
 
 	/* istate->initialized covers both .git/index and .git/sharedindex.xxx */
 	if (istate->initialized)
 		return istate->cache_nr;
 
+	start = getnanotime();
 	ret = do_read_index(istate, path, 0);
+	trace_performance_since(start, "read cache %s", path);
 
 	split_index = istate->split_index;
 	if (!split_index || is_null_sha1(split_index->base_sha1)) {
@@ -1897,6 +1902,7 @@ int read_index_from(struct index_state *istate, const char *path)
 
 	base_sha1_hex = sha1_to_hex(split_index->base_sha1);
 	base_path = git_path("sharedindex.%s", base_sha1_hex);
+	start = getnanotime();
 	ret = do_read_index(split_index->base, base_path, 1);
 	if (hashcmp(split_index->base_sha1, split_index->base->sha1))
 		die("broken index, expect %s in %s, got %s",
@@ -1906,6 +1912,9 @@ int read_index_from(struct index_state *istate, const char *path)
 	freshen_shared_index(base_sha1_hex, 0);
 	merge_base_index(istate);
 	post_read_index_from(istate);
+	trace_performance_since(start, "read cache %s",
+				git_path("sharedindex.%s",
+					 sha1_to_hex(split_index->base_sha1)));
 	return ret;
 }
 
@@ -2244,6 +2253,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 	struct ondisk_cache_entry_extended ondisk;
 	struct strbuf previous_name_buf = STRBUF_INIT, *previous_name;
 	int drop_cache_tree = 0;
+	uint64_t start = getnanotime();
 
 	for (i = removed = extended = 0; i < entries; i++) {
 		if (cache[i]->ce_flags & CE_REMOVE)
@@ -2374,6 +2384,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 		return -1;
 	istate->timestamp.sec = (unsigned int)st.st_mtime;
 	istate->timestamp.nsec = ST_MTIME_NSEC(st);
+	trace_performance_since(start, "write index, changed mask = %x", istate->cache_changed);
 	return 0;
 }
 
-- 
2.16.1.205.g271f633410