1572180 - 68 runs 3x slower than 67 on sample script

Status: NEW

(Core :: Performance, defect, P2)

Description

[Denis Palmeiro [:denispal]]

Attachment: firefox68Slow.html

This is quoted straight from bug 1565144 comment 9:

I have a relatively simple script that shows that 68.0.1 (and 68.0) runs about 3x slower than 67.0.4. The profiler shows that it is spending a lot more time GC-ing. Please see the attached HTML file.

This is with a fresh install, no add-ons or extensions.

I ran this on an 8 year old, 64-bit Intel i3-2310M quad-core (2.10 GHz) Windows 7 laptop with 8 GB of RAM. It takes about 300 seconds in 67.0.4, and about 900 seconds in 68.0.1. Scaling up to my actual product, what used to take 30 minutes takes almost 1.5 hours now.

It helps to set dom.max_script_run_time to a large number (I chose 10000000).

In 67.0.4, it's consistently takes about 3 seconds per 100000 iterations through the entire 10M loop. In 68.0.1, it starts slowing down (to 15 seconds per 100000 iterations) at around 5800000 (where the total size of the blobs is > 4 GB) and gets slower as the run progresses. The end result is a 3x increase in total time.

Hope this helps.

Comment 1

[Denis Palmeiro [:denispal]]

NI myself to bisect this.

Comment 2

[Denis Palmeiro [:denispal]]

I did try bisecting this at the time but couldn't find a culprit.