Analyzing Shutdown Performance

With the landing of bug 799640, the profiler add-on can now profile shutdown. I’ve created a dashboard that summarizes data from 10 of my shutdown profiles. Take a look at the dashboard here. You will find the shutdown profiles in the second section half way down the page. You’ll see 10 profiles under total or per function, clicking on any of them will open them in the preview and will filter by the function. Shutdown is at the end of the profile so I recommend focusing from the first pink shutdown marker and onward. You’ll see the following shutdown markers:

• Shutdown start: A shutdown has been requested.
• Shutdown early: Where we hope to call exit(0) eventually. Nearly everything after will not run with a few exceptions that will be moved before this point.
• Shutdown xpcom: Where we hope to call exit(0) soon.

What are we doing during shutdown? Here’s some trivia about my shutdowns:

• Takes from 1,000ms to 2,700ms making shutdown highly variable. As expected runs with higher uptime had slower shutdowns.
• Most of the shutdown time is spent doing GC/CC. This is because we persist data on destructors forcing us to clean up. This is getting fixed by exit(0) in bug 662444.
• Placing exit(0) at ‘Shutdown early’ would save between 1/3 to 2/3 of the shutdown time depending on the instance.
• Our shutdown is blocked by plugins because they may also need to persist data. Sadly this has to happen synchronously on the main thread and takes a consistent 90ms for me. We’re discussing options in bug 818265.
• Pages such as gmail.com block shutdown by running scripts on ‘page hide’ which is called on shutdown. This is unbounded but in my case was about 100ms.
• Startup and shutdown performance bugs are being tracked in bug 810156.
• Shutting down with less the 10 seconds of uptime will cause the startup cache to be saved on shutdown bug 816656.

After I’ve had time to study this data more I’m hoping gather performance data on other people’s profile to give a better sample of shutdown times since my Firefox profile is simple and I don’t stockpile 100s of tabs in my session like most do.