Thanks for reporting (and using m53)

A trace would help us understand what work is happening during this time. Here's how to capture it. https://www.chromium.org/developers/how-tos/trace-event-profiling-tool/recording-tracing-runs

Hit us up with a trace and we'll dig into it.

Trace attached.

Deleted: trace_Tue_Jul_19_2016_9.55.32_AM.json.gz.zip 16.2 MB

trace_Tue_Jul_19_2016_9.55.32_AM.json.gz.zip 16.2 MB Download

Thank you for providing more feedback. Adding requester "allada@chromium.org" for another review and adding "Needs-Review" label for tracking.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Still experience extreme slowness each time I go into debug mode on a daily basis. :-(

The issue seems much more prominent when I'm using my external monitor, which has a 4k display.

I've been experiencing this for a long time. Recently, this high CPU usage is accompanied by screen refreshes at a very high frequency (like in tight loop), and the browser page blinks a lot - with a perceived granularity of some medium (relative to screen size) squares.

Could you provide any instruction step by step, how to reproduce it?

I've disabled all my extensions / add-ons / plugins. This doesn't seem to make a difference.

Steps to reproduce:
1) Open devtools.
2) Reload site / app so that source maps are loaded and whatnot.
3) Set a break point.
4) Make the app reach the breakpoint.

Expected behavior:
The machine should be idling waiting for input on the console / actions on the dev tools UI.

Actual behavior:
- CPU goes to 100%.
- Main browser window starts blinking / flashing and you can see some kind of square grid with updated regions going white and then gray. (Note that this is a recent behavior and can be more visible due to the machine being a retina mbp 15 with no GPU. (no, intel integrated graphics don't count as GPU on my book :) )
- Resuming the application by pressing F8 / Play returns the CPU to normal level.

After tracing with the tools on "about:tracing", I realized that the screen a being repainted a lot - an hint was already given by the blinking / flashing described above.

This machine has an IGP (no discrete GPU) so, the extra painting is very hard on the general CPU.

Checking "Disable paused state overlay" apparently makes this behavior go away, will try/use dev tools for some more time until I provide a more firm confirmation.

Cleaning up "Needs-Review" label as we are not using this label for triage anymore. Ref bug for this cleanup 684919

Please reopen/file new issue if it's still a problem.