Config cache for system.xml loader: Speed improvement

app/code/core/Mage/Adminhtml/Model/Config.php

@@ -34,6 +34,15 @@
  */
 class Mage_Adminhtml_Model_Config extends Varien_Simplexml_Config
 {
+    /**
+     * @var string
+     */
+    protected $_cacheId = 'mage_adminhtml_config_system_xml';
+
+    /**
+     * @var Mage_Core_Model_Config_Base
+     */
+    protected $_config;
 
     /**
      * Enter description here...
@@ -80,16 +89,64 @@ public function getTabs()
         return $this->_tabs;
     }
 
+    public function __construct()
+    {
+        $this->_cacheChecksum = null;
+        $this->setCache(Mage::app()->getCache());
+        $this->setCacheTags([Mage_Core_Model_Config::CACHE_TAG]);
+        $usesCache = Mage::app()->useCache('config');
+        if (!$usesCache || !$this->loadCache()) {
+            /** @var Mage_Core_Model_Config_Base $config */
+            $this->_config = Mage::getConfig()->loadModulesConfiguration('system.xml')
+                ->applyExtends();
+            if ($usesCache) {
+                $this->saveCache();
+            }
+        }
+    }
+
+    /**
+     * @param $tags
+     * @return $this|Mage_Adminhtml_Model_Config
+     */
+    public function saveCache($tags=null)
+    {
+        if ($this->getCacheSaved()) {
+            return $this;
+        }
+        if (is_null($tags)) {
+            $tags = $this->_cacheTags;
+        }
+        $xmlString = $this->_config->getXmlString();
+        $this->_saveCache($xmlString, $this->getCacheId(), $tags, $this->getCacheLifetime());
+        $this->setCacheSaved(true);
+        return $this;
+    }
+
+    /**
+     * @return bool
+     */
+    public function loadCache()
+    {
+        $xmlString = $this->_loadCache($this->getCacheId());
+        $class = Mage::getConfig()->getModelClassName('core/config_base');
+        $this->_config = new $class();
+        libxml_use_internal_errors(true);
+        if (!empty($xmlString) && $this->_config->loadString($xmlString)) {
+            return true;
+        }
+        libxml_clear_errors();
+        return false;
+    }
+
     /**
      * Init modules configuration
      *
      * @return void
      */
     protected function _initSectionsAndTabs()
     {
-        $config = Mage::getConfig()->loadModulesConfiguration('system.xml')
-            ->applyExtends();
-
+        $config = $this->_config;
         Mage::dispatchEvent('adminhtml_init_system_config', array('config' => $config));
         $this->_sections = $config->getNode('sections');
         $this->_tabs = $config->getNode('tabs');

app/code/core/Mage/Core/etc/config.xml

@@ -122,7 +122,7 @@
             <types>
                 <config translate="label,description" module="core">
                     <label>Configuration</label>
-                    <description>System(config.xml, local.xml) and modules configuration files(config.xml).</description>
+                    <description>System (config.xml, local.xml) and modules configuration files (config.xml, system.xml).</description>
                     <tags>CONFIG</tags>
                 </config>
                 <layout translate="label,description" module="core">

app/locale/en_US/Mage_Core.csv

@@ -431,3 +431,4 @@
 "You will have to log in after you save your custom admin path.","You will have to log in after you save your custom admin path."
 "Your design change for the specified store intersects with another one, please specify another date range.","Your design change for the specified store intersects with another one, please specify another date range."
 "database ""%s""","database ""%s"""
+"System (config.xml, local.xml) and modules configuration files (config.xml, system.xml).","System (config.xml, local.xml) and modules configuration files (config.xml, system.xml)."