bcachefs: Optimize bch2_trans_init()

Now we store the transaction's fn idx in a local variable, instead of
redoing the lookup every time we call bch2_trans_init().
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/bcachefs.h

@@ -929,7 +929,6 @@ mempool_t		bio_bounce_pages;
 
 	struct bch2_time_stats	times[BCH_TIME_STAT_NR];
 
-	const char              *btree_transaction_fns[BCH_TRANSACTIONS_NR];
 	struct btree_transaction_stats btree_transaction_stats[BCH_TRANSACTIONS_NR];
 };
 

fs/bcachefs/btree_iter.c

@@ -2841,15 +2841,16 @@ static void bch2_trans_alloc_paths(struct btree_trans *trans, struct bch_fs *c)
 	trans->updates		= p; p += updates_bytes;
 }
 
-static inline unsigned bch2_trans_get_fn_idx(struct btree_trans *trans, struct bch_fs *c,
-					const char *fn)
+const char *bch2_btree_transaction_fns[BCH_TRANSACTIONS_NR];
+
+unsigned bch2_trans_get_fn_idx(const char *fn)
 {
 	unsigned i;
 
-	for (i = 0; i < ARRAY_SIZE(c->btree_transaction_fns); i++)
-		if (!c->btree_transaction_fns[i] ||
-		    c->btree_transaction_fns[i] == fn) {
-			c->btree_transaction_fns[i] = fn;
+	for (i = 0; i < ARRAY_SIZE(bch2_btree_transaction_fns); i++)
+		if (!bch2_btree_transaction_fns[i] ||
+		    bch2_btree_transaction_fns[i] == fn) {
+			bch2_btree_transaction_fns[i] = fn;
 			return i;
 		}
 
@@ -2857,16 +2858,17 @@ static inline unsigned bch2_trans_get_fn_idx(struct btree_trans *trans, struct b
 	return i;
 }
 
-void __bch2_trans_init(struct btree_trans *trans, struct bch_fs *c, const char *fn)
+void __bch2_trans_init(struct btree_trans *trans, struct bch_fs *c, unsigned fn_idx)
 	__acquires(&c->btree_trans_barrier)
 {
 	struct btree_transaction_stats *s;
 
 	memset(trans, 0, sizeof(*trans));
 	trans->c		= c;
-	trans->fn		= fn;
+	trans->fn		= fn_idx < ARRAY_SIZE(bch2_btree_transaction_fns)
+		? bch2_btree_transaction_fns[fn_idx] : NULL;
 	trans->last_begin_time	= local_clock();
-	trans->fn_idx		= bch2_trans_get_fn_idx(trans, c, fn);
+	trans->fn_idx		= fn_idx;
 	trans->locking_wait.task = current;
 	trans->journal_replay_not_finished =
 		!test_bit(JOURNAL_REPLAY_DONE, &c->journal.flags);

fs/bcachefs/btree_iter.h

@@ -587,10 +587,21 @@ void bch2_btree_path_to_text(struct printbuf *, struct btree_path *);
 void bch2_trans_paths_to_text(struct printbuf *, struct btree_trans *);
 void bch2_dump_trans_updates(struct btree_trans *);
 void bch2_dump_trans_paths_updates(struct btree_trans *);
-void __bch2_trans_init(struct btree_trans *, struct bch_fs *, const char *);
+void __bch2_trans_init(struct btree_trans *, struct bch_fs *, unsigned);
 void bch2_trans_exit(struct btree_trans *);
 
-#define bch2_trans_init(_trans, _c, _nr_iters, _mem) __bch2_trans_init(_trans, _c, __func__)
+extern const char *bch2_btree_transaction_fns[BCH_TRANSACTIONS_NR];
+unsigned bch2_trans_get_fn_idx(const char *);
+
+#define bch2_trans_init(_trans, _c, _nr_iters, _mem)			\
+do {									\
+	static unsigned trans_fn_idx;					\
+									\
+	if (unlikely(!trans_fn_idx))					\
+		trans_fn_idx = bch2_trans_get_fn_idx(__func__);		\
+									\
+	__bch2_trans_init(_trans, _c, trans_fn_idx);			\
+} while (0)
 
 void bch2_btree_trans_to_text(struct printbuf *, struct btree_trans *);
 

fs/bcachefs/debug.c

@@ -638,11 +638,11 @@ static ssize_t lock_held_stats_read(struct file *file, char __user *buf,
 		if (!i->size)
 			break;
 
-		if (i->iter == ARRAY_SIZE(c->btree_transaction_fns) ||
-		    !c->btree_transaction_fns[i->iter])
+		if (i->iter == ARRAY_SIZE(bch2_btree_transaction_fns) ||
+		    !bch2_btree_transaction_fns[i->iter])
 			break;
 
-		prt_printf(&i->buf, "%s: ", c->btree_transaction_fns[i->iter]);
+		prt_printf(&i->buf, "%s: ", bch2_btree_transaction_fns[i->iter]);
 		prt_newline(&i->buf);
 		printbuf_indent_add(&i->buf, 2);