From 87bab705ded31559941020d3c500f43f571f9c16 Mon Sep 17 00:00:00 2001
From: "Bradley T. Hughes" <bradley.hughes@nokia.com>
Date: Fri, 1 Oct 2010 09:45:42 +0200
Subject: Disable spinning under lock contention on single CPU machines

Spinning is just wasted time on these systems.

Reviewed-by: joao
---
 src/corelib/thread/qmutex.cpp | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/corelib/thread/qmutex.cpp b/src/corelib/thread/qmutex.cpp
index 19e2457..54b3ed4 100644
--- a/src/corelib/thread/qmutex.cpp
+++ b/src/corelib/thread/qmutex.cpp
@@ -429,6 +429,16 @@ void QMutex::unlock()
 void QMutex::lockInternal()
 {
     QMutexPrivate *d = static_cast<QMutexPrivate *>(this->d);
+
+    if (QThread::idealThreadCount() == 1) {
+        // don't spin on single cpu machines
+        bool isLocked = d->wait();
+        Q_ASSERT_X(isLocked, "QMutex::lock",
+                   "Internal error, infinite wait has timed out.");
+        Q_UNUSED(isLocked);
+        return;
+    }
+
     int spinCount = 0;
     int lastSpinCount = d->lastSpinCount;
 
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