Skip filtering during push if there are no push actions

synapse/push/bulk_push_rule_evaluator.py

@@ -332,6 +332,11 @@ async def action_for_event_by_user(
                 # Push rules say we should notify the user of this event
                 actions_by_user[uid] = actions
 
+        # If there aren't any actions then we can skip the rest of the
+        # processing.
+        if not actions_by_user:
+            return
+
         # This is a check for the case where user joins a room without being
         # allowed to see history, and then the server receives a delayed event
         # from before the user joined, which they should not be pushed for

synapse/visibility.py

@@ -162,6 +162,10 @@ async def filter_event_for_clients_with_state(
     if event.internal_metadata.is_soft_failed():
         return []
 
+    # Fast path if we don't have any user IDs to check.
+    if not user_ids:
+        return ()
+
     # Make a set for all user IDs that haven't been filtered out by a check.
     allowed_user_ids = set(user_ids)