Open Radar

 
After updating my iPhone 5s to iOS 8 GM, I began to notice that some interactions were ever-so-slighty slower than before. Most noticeably, the keyboard wasn't as responsive as I was used to, which caused my typing skills to suffer. However, I didn't think too much of it, and figured it was nothing to worry about.
 
However, I then tried running a certain open source app , which although quite complex, ran perfectly fine on my 5s with around 20-30% CPU usage on iOS 7. On iOS 8, the app however does not even run full speed; frames are dropped every few seconds or so, and the audio is skipped. I looked at Xcode's Debug Session pane, and saw it was using 90-110% of the CPU.
 
Digging deeper, I ran the app on both my iPhone 5s on iOS 8 and my iPad Air on iOS 7, and profiled their performance. Both devices have approximately the same processing power, so their numbers should theoretically be rather close (with the Air potentially being a bit faster).
 
RESULTS (10 seconds peforming the same task):
 
iPad Air: 2689ms
iPhone 5s: 9076ms
 
During 10 seconds of rendering the same thing, the iPhone spent almost 4 times as much time on the CPU as the iPad Air. In addition, the iPhone was still using 90-110% of the CPU, while the iPad Air ran consistently at around 25-33%. Even more fun is there is no particular method that was to blame, all methods ran approximately 4x slower. Put another way, the app was taking four times as long to drive the game engine, and also taking four times as long to render each frame.
 
Here are links to the two Instruments files I used to test this. I ran both devices for 50 seconds, and then measured the performance in a 10 second window.
iOS 7 (iPad Air): https://dl.dropboxusercontent.com/u/14828584/iOS%207%20Performance.trace.zip
iOS 8 (iPhone 5s): https://dl.dropboxusercontent.com/u/14828584/iOS%208%20Performance.trace.zip
 
I'm really hoping this is a bug, and that this will be fixed soon. My iPhone 5s was extraordinarily fast on iOS 7; on iOS 8, this simply isn't the case.