From f7d7c246b8b76cbd4440b9c1665f0ccaa57e9880 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Gr=C3=A4=C3=9Flin?= <mgraesslin@kde.org>
Date: Thu, 15 Jan 2015 08:32:11 +0100
Subject: [PATCH] Slightly optimize Workspace::xStackingOrder

Callgrind analysis showed that this method has room for improvement.
The bottle neck is mapping the Unmanaged against the list of windows
retreived from xcb_query_tree. The number of windows in that list is
rather large (>1000), which turns the loop into an expensive path.
Workspace::findUnmanaged seems to be too expensive for that due to the
overhead of using a functor and multiple method calls. The Inl. cost
before the optimization for checking ~55,000 windows is 2.46.

The change uses a good old const-iterator based loop over the unmanaged
list to check for the window. This reduces the Incl. cost for checking
~55,000 windows to 0.28.

REVIEW: 122067
---
 layers.cpp | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/layers.cpp b/layers.cpp
index 8b49f29615..e95305e110 100644
--- a/layers.cpp
+++ b/layers.cpp
@@ -670,11 +670,22 @@ ToplevelList Workspace::xStackingOrder() const
     x_stacking.append(c);
 
     xcb_window_t *windows = tree.children();
+    const auto count = tree->children_len;
+    int foundUnmanagedCount = unmanaged.count();
     for (unsigned int i = 0;
-            i < tree->children_len;
+            i < count;
             ++i) {
-        if (Unmanaged* c = findUnmanaged(windows[i]))
-            x_stacking.append(c);
+        for (auto it = unmanaged.constBegin(); it != unmanaged.constEnd(); ++it) {
+            Unmanaged *u = *it;
+            if (u->window() == windows[i]) {
+                x_stacking.append(u);
+                foundUnmanagedCount--;
+                break;
+            }
+        }
+        if (foundUnmanagedCount == 0) {
+            break;
+        }
     }
     if (m_compositor) {
         const_cast< Workspace* >(this)->m_compositor->checkUnredirect();