问题
After upgraded to xcode 6 I found that when I run my app under iOS 8 in iOS simulator, it ran very slowly, no matter when I choose iPhone or iPad. But if I choose it to run under iOS 7 it ran normally. I was thinking that it was an app/coding related problem so then I tried to deploy it on my ipad with iOS8 and strangely the app run normally, not as slow as simulator does Does anybody on SO experience this issue?
回答1:
Performance in the iOS Simulator is not expected to match performance on device. The iOS Simulator is meant as a tool for rapid prototyping and fast iteration. Performance tuning needs to be done on real devices.
Processes running in the iOS Simulator are basically OS X processes running in a specially crafted runtime within a special bootstrap to behave like iOS rather than OS X. Over the past 4 years, this has evolved from basically UIKit and similar iOS Frameworks built on top of OS X Frameworks to now having our own bootstrap server (as of iOS 7), our own dyld (as of iOS 8), and only sharing the host kernel and very low level system libraries (libSystem as of iOS 7, and just the pthreads, syscalls, and platform children of libSystem as of iOS 8).
When you test an app on a device that is not currently booted, we shutdown the device and boot the new one, and that process can take 10s to a minute or 2 to complete based primarily on your disk's I/O bandwidth and what other tasks on your system are demanding of it.
If you see major performance issues with a sim device that has been booted for a while and don't have any obvious background tasks running (compilation, rsync, whatever), take a sysdiagnose and take a look at the simulator processes in the spin dump and fs_usage to see what's likely going on.
回答2:
Make sure 'slow animations' is not selected under the Debug tab in the iOS Simulator. That fixed the issue for me. It might have been turned on by accident.
回答3:
If you hit ⌘T while your simulator is selected it will turn on 'slow animations' which puts everything in slow motion. ⌘T is often used to open up a new browser tab, so just be sure your browser is selected and not your simulator.
回答4:
Performance simulation and device different things. I think you should not pay attention to it. This error can optimize apple
来源：https://stackoverflow.com/questions/26152919/slow-app-performance-under-ios-8-simulator-with-xcode-6