While using the timeline, I often see paint operations starting at the exact same time and then overlapping. As far as I understand how we record markers, it should be impossible to have overlapping painting operations.

This looks wrong indeed.

Any idea what's going on?

We're missing a marker that ends a paint.

Good catch, that explains why we see several paint markers all ending at the same time.

So this is linked to bug 1071056?

(In reply to Patrick Brosset [:pbrosset] [:patrick] from comment #5) > So this is linked to bug 1071056? No.

<style> p:hover{font-size: 20px} </style> <p id="foo">X</p> This code can trigger this pattern: > paint > reflow > paint > style With the first paint ending where the second paint ends. The first paint should not exist. So I believe the issue is not that we're missing a END marker, but we have an extra START marker.

This only happens on firefox desktop with the toolbox docked in the browser. If you undock the toolbox in its own window, there's only one paint per hover anymore. The extra paint comes from the timeline itself that refreshes while recording. It also happen if you focus the URL bar (so that the caret blinks) and hover the <p> node. Start/End markers always come in pairs within a tick, so it's not a problem that we have an extra start, but rather a problem that the code in nsDocShell::PopProfileTimelineMarkers fails at pairing Start and End paint markers correctly.

So the problem was that we weren't breaking out of the nested for loop if we met a start/end paint pair but no layer event in between, which means that we were then iterating until we did find a layer event.

Pending try build: https://tbpl.mozilla.org/?tree=Try&rev=0f153a814518

Reproduced the bug on Nightly 35.0a1 (2014-09-11), using Windows 7 64-bit. Verified fixed on Aurora 35.0a2 (2014-10-28 / 20141028155607) and Nightly 36.0a1 (2014-10-28), using Windows 7 64-bit, Ubuntu 14.04 LTS 32-bit and Mac OS X 10.9.5.

Sorry for the spam. Moving bugs to Firefox :: Developer Tools: Performance Tools (Profiler/Timeline). dkl