the Inclusive Wall Time of Current function bigger than all Child functions

the Inclusive Wall Time of current function is : 30,321us
and the total Inclusive Wall Time of all children function is less than 15,000us,
why ? I think the two time should nearly equal.
and the code is :

 protected function getTableMetadata($name, $type, $refresh)
    {
        $cache = null;
        if ($this->db->enableSchemaCache && !in_array($name, $this->db->schemaCacheExclude, true)) {
            $schemaCache = is_string($this->db->schemaCache) ? Yii::$app->get($this->db->schemaCache, false) : $this->db->schemaCache;
            if ($schemaCache instanceof Cache) {
                $cache = $schemaCache;
            }
        }
        $rawName = $this->getRawTableName($name);
        if ($refresh || !isset($this->_tableMetadata[$rawName])) {
            $this->loadTableMetadataFromCache($cache, $rawName);
        }
        if (!array_key_exists($type, $this->_tableMetadata[$rawName])) {
            $this->_tableMetadata[$rawName][$type] = $this->{'loadTable' . ucfirst($type)}($rawName);
            $this->saveTableMetadataToCache($cache, $rawName);
        }

        return $this->_tableMetadata[$rawName][$type];
    }

thank you very much!

Start by locating getTableMetadata and the profiler code that calculates inclusive wall time and aggregates child functions. Compare the reported parent and child timings using the attached example and trace data. Done means establishing whether the discrepancy is expected or identifying a concrete timing-calculation defect.