Compiling the attribute value and then calling it is heavy. Nearly 80% of *event dispatch time* in a testcase is spent in nsEventListenerManager::CompileEventHandlerInternal and nsJSEventListener::HandleEvent (Includes the time, 11.6%, which is spent to really call the JS function.) Slow-looking things are for example nsScriptSecurityManager::CheckFunctionAccess and often used JS context stack push/pop. JS_CompileUCFunctionForPrincipals (17%) could be optimized too, I hope.

Olli, do you want to either mail me the .mshark file for that or put it somewhere where I can get at it? I assume it's too big to attach to this bug?

We cache compiled event handlers, IIRC, so this is first-click (just checking)? It would be great to see the hierarchical profile data. /be

We do cache compiled event handlers, but the first case the handler is called/compiled, we spend lots of time compiling/binding it.

How about now?

Need to reprofile compilation.

Situation isn't any better. Compilation seems to be still slow. Bug 517385 has a testcase.

Actually, since event dispatch itself is faster, compilation takes even more % from the total time.

https://bugzilla.mozilla.org/show_bug.cgi?id=1472046 Move all DOM bugs that haven’t been updated in more than 3 years and has no one currently assigned to P5. If you have questions, please contact :mdaly.