I have an app which I am trying to migrate to a new project. There is a heavy operation which I am handling in main thread asynchronously. In my older project, it takes just a second to complete this task but in my new project, it takes 6-7 seconds for the same task.
I observed the CPU usage and it looks like the new app is using less CPU and getting very few threads while the old one gets lots of threads for the same task. PS: I am using the same device.
What could cause this? Any ideas or suggestions to find out?
Thanks.
Finally, I found the problem. It was caused by Optimization Level setting in Xcode Build Settings. When a new project created, default Debug optimization level is none, and Release optimization level is Fastest, Smallest [-Os] So when I changed Debug to Fastest, Smallest [-Os] my task completion time dropped to 1 sec.
From Apple:
The Xcode compiler supports optimization options that let you choose whether you prefer a smaller binary size, faster code, or faster build times. For new projects, Xcode automatically disables optimizations for the debug build configuration and selects the Fastest, Smallest option for the release build configuration. Code optimizations of any kind result in slower build times because of the extra work involved in the optimization process. If your code is changing, as it does during the development cycle, you do not want optimizations enabled. As you near the end of your development cycle, though, the release build configuration can give you an indication of the size of your finished product, so the Fastest, Smallest option is appropriate.
If you want to read more about optimization levels and performance: Tuning for Performance and Responsiveness
Side note: Changing the optimization level to fastest, Smallest [-0s] in debug mode might affect the debugger breakpoints and it will behave abruptly.
Cheers.