bcachefs: Switch to local_clock() for fastpath time source

local_clock() isn't always completely accurate - e.g. on machines with
TSC drift - but ktime_get_ns() overhead is too high, unfortunately.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_iter.c

@@ -2787,7 +2787,7 @@ u32 bch2_trans_begin(struct btree_trans *trans)
 
 	if (!trans->restarted &&
 	    (need_resched() ||
-	     ktime_get_ns() - trans->last_begin_time > BTREE_TRANS_MAX_LOCK_HOLD_TIME_NS)) {
+	     local_clock() - trans->last_begin_time > BTREE_TRANS_MAX_LOCK_HOLD_TIME_NS)) {
 		bch2_trans_unlock(trans);
 		cond_resched();
 		bch2_trans_relock(trans);
@@ -2797,7 +2797,7 @@ u32 bch2_trans_begin(struct btree_trans *trans)
 	if (trans->restarted)
 		bch2_btree_path_traverse_all(trans);
 
-	trans->last_begin_time = ktime_get_ns();
+	trans->last_begin_time = local_clock();
 	return trans->restart_count;
 }
 
@@ -2851,7 +2851,7 @@ void __bch2_trans_init(struct btree_trans *trans, struct bch_fs *c, const char *
 	memset(trans, 0, sizeof(*trans));
 	trans->c		= c;
 	trans->fn		= fn;
-	trans->last_begin_time	= ktime_get_ns();
+	trans->last_begin_time	= local_clock();
 	trans->fn_idx		= bch2_trans_get_fn_idx(trans, c, fn);
 	trans->locking_wait.task = current;
 	trans->journal_replay_not_finished =

fs/bcachefs/btree_locking.h

@@ -87,7 +87,7 @@ static inline void mark_btree_node_locked(struct btree_trans *trans,
 {
 	mark_btree_node_locked_noreset(path, level, type);
 #ifdef CONFIG_BCACHEFS_LOCK_TIME_STATS
-	path->l[level].lock_taken_time = ktime_get_ns();
+	path->l[level].lock_taken_time = local_clock();
 #endif
 }
 
@@ -119,7 +119,7 @@ static void btree_trans_lock_hold_time_update(struct btree_trans *trans,
 	if (s)
 		__bch2_time_stats_update(&s->lock_hold_times,
 					 path->l[level].lock_taken_time,
-					 ktime_get_ns());
+					 local_clock());
 #endif
 }
 
@@ -259,7 +259,7 @@ static inline int btree_node_lock(struct btree_trans *trans,
 	    btree_node_lock_increment(trans, b, level, type) ||
 	    !(ret = btree_node_lock_nopath(trans, b, type))) {
 #ifdef CONFIG_BCACHEFS_LOCK_TIME_STATS
-		path->l[b->level].lock_taken_time = ktime_get_ns();
+		path->l[b->level].lock_taken_time = local_clock();
 #endif
 	}