Closed Bug 1542232 Opened 5 years ago Closed 5 years ago

Investigate win10-pgo-qr-only startup_about_home_paint regression as a result of idle new tab preloading


(Firefox :: Tabbed Browser, defect, P1)




Tracking Status
firefox68 --- affected


(Reporter: Gijs, Assigned: Gijs)




(Keywords: regression)

Splitting this off from bug 1537694 - :igoldan, can you update the perfherder stuff to point to this bug?

(In reply to Ionuț Goldan [:igoldan], Performance Sheriffing from bug 1537694 comment #7)

I also noticed a Talos regression:

== Change summary for alert #20026 (as of Thu, 21 Mar 2019 05:48:40 GMT) ==


6% startup_about_home_paint windows10-64-pgo-qr opt e10s stylo 676.08 -> 714.79

For up to date results, see:

These are the Gecko profiles for it:



Flags: needinfo?(igoldan)


Flags: needinfo?(igoldan)
Priority: -- → P1

Felipe pointed out that in he saw similar effects...

(In reply to :Gijs (he/him) from comment #3)

Pushed to try thrice:

  1. baseline:

  2. backing out initializing the preloaded tab in the new window:

  3. backing out all of bug 1353013:

Even backing everything out doesn't return nearly as big a gap as appeared in the runs on autoland, and perf compare isn't confident that it's an improvement even with 15 runs of the job on each push. This test is pretty noisy...

My best guess is that we're somehow starting the load of the preloaded browser early some of the time and that interferes with things. This wasn't brought out in the profiles per mconley's analysis in bug 1537694 comment 21, but it's possible that the profiler interferes with things to the point where that run isn't representative for what happens without the profiler.

I guess we could delay preloading until after the initial about:home tab has loaded, if indeed we're loading about:home on startup, which hopefully would deal with that?

Then again, given that just not running the initial preload at all makes very little difference ( ), I wonder if it's even worth doing that, and if we should just accept the regression and move on with life... if there was something more serious going on I'd expect regressions on the other platforms, too.

I also can't reproduce any differences locally on my own windows build. Just noise.

Thoughts, Mike? Are there obvious causes/issues I'm missing here?

Flags: needinfo?(mconley)

I think we've done our due diligence here. Sometimes these tests catch regressions that we can do something about. Sometimes they don't. I think this is one of the times that they don't. I think we need to just eat this one in the interest of better preloading behaviour.

Flags: needinfo?(mconley)

Alright, let's call it.

Closed: 5 years ago
Resolution: --- → WONTFIX
Has Regression Range: --- → yes
Keywords: regression
You need to log in before you can comment on or make changes to this bug.