What causes large white space in the timeline?

Hi Pat,

I’ve ran a few tests recently and I’m seeing unexpected dead time, white space, in the timeline.

Any ideas what may cause this?

This result Amsterdam Chrome shows it:

While this one, Paris Chrome doesn’t:

Sometimes it can be rather extreme like this London IE8:



Hmm, usually it’s script running or something else eating CPU but the Amsterdam CPU utilization wasn’t an issue (looked to be a problem with London). The best bet is usually to capture a dev tools timeline which will tell you what Chrome is doing (option in the Chrome tab of advanced settings).

I re-ran amsterdam and it looks like Chrome is doing “Layout” but it doesn’t really break it down more than that: http://www.webpagetest.org/timeline/28/timeline.php?test=131030_XQ_173M&run=1

Thanks Pat