Open Radar

 
Summary:
On an iOS 8 action extension the performance of WKWebView is throttled, especially when compared to the performance of the same exact code outside of the action extension.

Steps to Reproduce:
1. Download the attached package and open the ExtensionTest sample project.
2. Run the regular app and complete the Octane benchmark. Note the performance metrics.
3. Run the extension (featuring identical code, namely WKWebView) and complete the Octane benchmark. Note the performance metrics.
4. Compare the two sets of metrics.

Expected Results:
Since an action extension operates in a memory constrained environment, it is expected that it's performance will be somewhat throttled. We expected a single order of magnitude or better difference between the two sets of results.

Actual Results:
The measures for memory, garbage collection, and compiler latency show an extremely high two order of magnitude (100x) difference in performance. This performance profile is seen on the iPhone 6 Plus, which has the most performant hardware in the iPhone line. An action extension run on an iPhone 5S was not able to complete the Octane benchmark within a reasonable time frame.

Since most web applications typically make heavy use of JavaScript and it's garbage collector, these metrics indicate that their performance would be highly impaired when run inside of an action extension.

This is happens despite the use of WKWebView, which is makes use of all available JS runtime optimizations on iOS and use of the latest hardware. (iPhone 6 Plus)

Version:
iOS 8.1 (12B411)

Notes:
See the report (available in PDF and Pages formats) in the attached package indicating the exact performance numbers as well as device screenshots.

Configuration:
iPhone 6 Plus 16GB