Why WKWebView seems to lack CPU ressources while monitor says CPU usage is under 20%?

Hi,
I am currently developping a JS app hosted in a WKWebView and facing two issues only on iOS.
My app use heavy computation in in real-time and I encoutered the following issues:

  • The computation is almost 20 times slower on new IPad 2 Air than on a low end ChromeBook
  • While the computation seems affect global app responsivness and graphic rendering, monitoring the CPU using Xcode shows that its usage does not exceeds 20% and that there is plenty of free memory space.

Would anybody have an idea about the sources of this two issues?