I'm using OpenGL ES 1.1 and CADisplayLink to animate a 3d scene. If the iOS device has been rebooted fairly recently, the animation is smooth and the time delta between two displayLink.timestamp calls is fairly even. But after a few hours or days of the iOS device being used and my app is sometimes run a few times, the animation becomes jerky and the time deltas ramp up and then reset to a lower value only to ramp up again. Like this: 2012-09-01 23:42:58.770 [2678:707] dt= 0.021139 2012-09-01 23:42:58.787 [2678:707] dt= 0.022183 2012-09-01 23:42:58.804 [2678:707] dt= 0.023223 2012-09-01 23:42:58.820 [2678:707] dt= 0.024270 2012-09-01 23:42:58.837 [2678:707] dt= 0.009679 2012-09-01 23:42:58.853 [2678:707] dt= 0.010750 2012-09-01 23:42:58.870 [2678:707] dt= 0.011766 2012-09-01 23:42:58.887 [2678:707] dt= 0.012806 2012-09-01 23:42:58.903 [2678:707] dt= 0.013847 2012-09-01 23:42:58.920 [2678:707] dt= 0.014890 2012-09-01 23:42:58.937 [2678:707] dt= 0.015933 2012-09-01 23:42:58.953 [2678:707] dt= 0.016976 2012-09-01 23:42:58.970 [2678:707] dt= 0.018011 2012-09-01 23:42:58.987 [2678:707] dt= 0.019055 2012-09-01 23:42:59.003 [2678:707] dt= 0.020097 2012-09-01 23:42:59.020 [2678:707] dt= 0.021143 2012-09-01 23:42:59.037 [2678:707] dt= 0.022181 2012-09-01 23:42:59.054 [2678:707] dt= 0.023222 2012-09-01 23:42:59.071 [2678:707] dt= 0.024288 2012-09-01 23:42:59.087 [2678:707] dt= 0.009624 2012-09-01 23:42:59.103 [2678:707] dt= 0.010728 2012-09-01 23:42:59.121 [2678:707] dt= 0.011763 2012-09-01 23:42:59.137 [2678:707] dt= 0.012808 2012-09-01 23:42:59.153 [2678:707] dt= 0.013847 2012-09-01 23:42:59.170 [2678:707] dt= 0.014891 2012-09-01 23:42:59.187 [2678:707] dt= 0.016002 2012-09-01 23:42:59.203 [2678:707] dt= 0.016979 2012-09-01 23:42:59.220 [2678:707] dt= 0.018016 2012-09-01 23:42:59.237 [2678:707] dt= 0.019042 2012-09-01 23:42:59.253 [2678:707] dt= 0.020099 2012-09-01 23:42:59.270 [2678:707] dt= 0.021138 2012-09-01 23:42:59.287 [2678:707] dt= 0.022185 2012-09-01 23:42:59.304 [2678:707] dt= 0.023222 2012-09-01 23:42:59.320 [2678:707] dt= 0.024265 2012-09-01 23:42:59.337 [2678:707] dt= 0.009681 2012-09-01 23:42:59.354 [2678:707] dt= 0.010736 And then if the iOS device is rebooted the animation is smooth again. The problem even occurs on my menu screen when almost no game related calculations are going on in the UpdateAnimation() function. I don't understand what is going on and why a fresh reboot will always fix this problem for a while.