diff --git a/application/loginform.class.inc.php b/application/loginform.class.inc.php
index 51f1e3832..4b55ca757 100644
--- a/application/loginform.class.inc.php
+++ b/application/loginform.class.inc.php
@@ -51,10 +51,8 @@ class LoginForm extends AbstractLoginFSMExtension implements iLoginUIExtension
 				$this->bForceFormOnError = false;
 				exit;
 			}
-			Session::Start();
 			Session::Set('login_temp_auth_user', $sAuthUser);
 			Session::Set('login_mode', 'form');
-			Session::WriteClose();
 		}
 		return LoginWebPage::LOGIN_FSM_CONTINUE;
 	}
diff --git a/application/loginwebpage.class.inc.php b/application/loginwebpage.class.inc.php
index 4e3cc7c56..6dec4e565 100644
--- a/application/loginwebpage.class.inc.php
+++ b/application/loginwebpage.class.inc.php
@@ -394,14 +394,12 @@ class LoginWebPage extends NiceWebPage
 	public static function ResetSession()
 	{
 		// Unset all of the session variables.
-		Session::Start();
 		Session::Unset('auth_user');
 		Session::Unset('login_state');
 		Session::Unset('can_logoff');
 		Session::Unset('archive_mode');
 		Session::Unset('impersonate_user');
 		UserRights::_ResetSessionCache();
-		Session::WriteClose();
 		// If it's desired to kill the session, also delete the session cookie.
 		// Note: This will destroy the session, and not just the session data!
 	}
@@ -669,10 +667,8 @@ class LoginWebPage extends NiceWebPage
 			$oLog->DBInsertNoReload();
 		}
 
-		Session::Start();
 		Session::Set('auth_user', $sAuthUser);
 		Session::Set('login_mode', $sLoginMode);
-		Session::WriteClose();
 		UserRights::_InitSessionCache();
 	}
 
@@ -1017,7 +1013,6 @@ class LoginWebPage extends NiceWebPage
 		$sMessage = self::HandleOperations($operation); // May exit directly
 	
 		$iRet = self::Login($iOnExit);
-	
 		if ($iRet == self::EXIT_CODE_OK)
 		{
 			if ($bMustBeAdmin && !UserRights::IsAdministrator())
diff --git a/application/startup.inc.php b/application/startup.inc.php
index 534212a7e..c414f2251 100644
--- a/application/startup.inc.php
+++ b/application/startup.inc.php
@@ -68,9 +68,10 @@ register_shutdown_function(function()
 		}
 	}
 });
-
+$oKPI = new ExecutionKPI();
 Session::Start();
 Session::WriteClose();
+$oKPI->ComputeAndReport("Session Start");
 
 $sSwitchEnv = utils::ReadParam('switch_env', null);
 $bAllowCache = true;
diff --git a/core/userrights.class.inc.php b/core/userrights.class.inc.php
index 448f64027..2a8f22cd5 100644
--- a/core/userrights.class.inc.php
+++ b/core/userrights.class.inc.php
@@ -1795,10 +1795,6 @@ class UserRights
 			self::$m_aAdmins = array();
 			self::$m_aPortalUsers = array();
 		}
-		if (!utils::IsModeCLI())
-		{
-			Session::Start();
-		}
 		self::_ResetSessionCache();
 		if (self::$m_oAddOn)
 		{
@@ -1905,10 +1901,8 @@ class UserRights
 
 	public static function _ResetSessionCache()
 	{
-		Session::Start();
 		Session::Unset('profile_list');
 		Session::Unset('archive_allowed');
-		Session::WriteClose();
 	}
 	
 	/**
diff --git a/datamodels/2.x/authent-cas/src/CASLoginExtension.php b/datamodels/2.x/authent-cas/src/CASLoginExtension.php
index 3c6fe7839..71a8e1277 100644
--- a/datamodels/2.x/authent-cas/src/CASLoginExtension.php
+++ b/datamodels/2.x/authent-cas/src/CASLoginExtension.php
@@ -49,7 +49,6 @@ class CASLoginExtension extends AbstractLoginFSMExtension implements iLogoutExte
 	{
 		if (Session::Get('login_mode') == 'cas')
 		{
-			Session::Start();
 			static::InitCASClient();
 			if (phpCAS::isAuthenticated())
 			{
@@ -72,7 +71,6 @@ class CASLoginExtension extends AbstractLoginFSMExtension implements iLogoutExte
 				Session::Set('login_mode', 'cas');
 				phpCAS::forceAuthentication(); // Redirect to CAS and exit
 			}
-			Session::WriteClose();
 		}
 		return LoginWebPage::LOGIN_FSM_CONTINUE;
 	}
diff --git a/pages/exec.php b/pages/exec.php
index e271f3972..37831d4d1 100644
--- a/pages/exec.php
+++ b/pages/exec.php
@@ -43,9 +43,11 @@ if ($sPage == '')
 }
 $sPage = basename($sPage); // protect against ../.. ...
 
+$oKPI = new ExecutionKPI();
 Session::Start();
 $sEnvironment = utils::ReadParam('exec_env', utils::GetCurrentEnvironment());
 Session::WriteClose();
+$oKPI->ComputeAndReport("Session Start");
 
 $sTargetPage = APPROOT.'env-'.$sEnvironment.'/'.$sModule.'/'.$sPage;
 
diff --git a/sources/application/Helper/Session.php b/sources/application/Helper/Session.php
index 970803475..5a8a820c2 100644
--- a/sources/application/Helper/Session.php
+++ b/sources/application/Helper/Session.php
@@ -7,8 +7,6 @@
 
 namespace Combodo\iTop\Application\Helper;
 
-use ExecutionKPI;
-
 /**
  * Session management
  * Allow early session close to have multiple ajax calls in parallel
@@ -26,7 +24,6 @@ class Session
 	{
 		self::$bIsInitialized = true;
 		if (!self::$bSessionStarted) {
-			$oKPI = new ExecutionKPI();
 			session_name('itop-'.md5(APPROOT));
 			if (!is_null(self::$iSessionId)) {
 				session_id(self::$iSessionId);
@@ -35,17 +32,14 @@ class Session
 				self::$bSessionStarted = session_start();
 				self::$iSessionId = session_id();
 			}
-			$oKPI->ComputeAndReport("Session Start");
 		}
 	}
 
 	public static function WriteClose()
 	{
 		if (self::$bSessionStarted) {
-			$oKPI = new ExecutionKPI();
 			session_write_close();
 			self::$bSessionStarted = false;
-			$oKPI->ComputeAndReport("Session Write Close");
 		}
 	}
 
@@ -55,6 +49,9 @@ class Session
 	 */
 	public static function Set($key, $value)
 	{
+		if (self::Get($key) == $value) {
+			return;
+		}
 		$aSession = $_SESSION;
 		$sSessionVar = &$aSession;
 		if (is_array($key)) {