Nano Adblocker is spending > 70ms during requestAnimationFrame

[jrmuizel]

Nano Adblocker is spending > 70ms during requestAnimationFrame. This will have a very negative impact on performance.

Here's a link to a profile showing the problem: https://perfht.ml/32Hyqxo

[jrmuizel]

The bulk of the time is spent doing selector matching on a bunch of selectors.

[jspenguin2017]

Can't reproduce, you need to fill the template.

[jrmuizel]

The user that made the profile says that it was on facebook or reddit. I've asked for more details.

[jspenguin2017]

I tested Facebook on my four years old tablet, the animation frame handler takes up to 15 ms. Note that this only happen from time to time, and not every animation frame. The website runs pretty smoothly.

[jspenguin2017]

I am going to close this since you did not fill the template. Keep in mind that I do not maintain the Firefox build. If you can reproduce the issue on Chrome, feel free to open another issue with completed template and detailed reproduction steps.

[gorhill]

@jrmuizel

From what I can see, the bulk of the time is spent enforcing procedural cosmetic filters. The user would need to disclose what are these procedural cosmetic filters -- filter list authors are aware that these sort of filters have to be used parsimoniously. Facebook's site however makes it difficult for content blockers to do their job and last time the site required the use of complex procedural filters.

Also, the procedural cosmetic filters code will disable procedural cosmetic filters which are found to be performance bottleneck. As per profiling, the procedural filters uses 1,332 / 20,000ms or ~6.5%, probably below the threshold of what is considered a performance bottleneck.

Now for the specific profiling results you shared, we really need more information as to how the user configured his content blocker (which is essentially at its core uBlock Origin) -- I don't think it's normal for the code to spend so much time in querySelectorAll() -- this suggests some bad filters are being in use. For instance, when I expand Element.querySelectorAll in the profiler, I see a lot of entries like so:

These are not part of the default filter lists, and this suggests the user created too many procedural filters.

[gorhill]

Related bugzilla issue: https://bugzilla.mozilla.org/show_bug.cgi?id=1633409.