What do the striped grey areas in the chrome CPU timeline mean?

Question

There\'s significant CPU usage shown here, but no reason given. Timeline taken from Android Chrome v51.

Answer 1

Grey means that DevTools is aware of the activity but doesn't know the identity of it.

Striped means activity that is off of the main thread.

So, grey and striped means unidentified activity that is not occurring in the main thread.

Gold and striped means script activity off the main thread. This is typically a worker, though ScriptStreamer can show up too. (ScriptStreamer wasn't really instrumented well before Chrome 77.) Collapse the "Main Thread" section to see what's beneath it.

Gold, purple, green and striped means script & rendering activity off the main thread. That's most likely coming from out-of-process iframes. Again, you can collapse the "Main Thread" section to more easily explore the other threads.

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If you're seeing lots of gray in the overview (striped or not), it indicates DevTools isn't showing you details on the activity. In this case, you can file a bug to provide more information. Capture a full trace (using chrome://tracing) and open a ticket on crbug.com so that DevTools team can diagnose more.

You can also turn on hidden DevTools experiments and then select "Timeline: show all events" to have the flamechart show everything it knows about.