Snappy, July 26: Go Try The Gecko Profiler!

See raw notes for details on mid-flight snappy work.

Checkout the SPS Profiler!

SPS Gecko Profiler has gotten a lot of praise this week on #perf. If you ever wonder the hell Firefox is doing with your CPU, give the profiler a try. For the past couple of weeks it has been able to label stacks with JS, URLs and even favicons. It’s likely that Mozilla may have shipped the world’s first profiler to feature favicons.

Having JS support is nice, it lead to the first 2 snappy addon bugs: 777266, 777397. I documented how to act on addon responsiveness issues in the snappy wiki.

Whether you develop web pages, addons or are a core gecko hacker, the profiler may make the performance-analysis part of your life much more pleasant. Update: Benoit Girard wrote about the new profiler features.

Things To Not Do On Startup

Blair McBride did some digging, there may be 15million users with signed extensions which can cause Firefox to do network IO (ie stall for a long time) on startup.

Brian Bondy landed a fix to lower IO priority of nuking our cache: 773518. According to telemetry, 10-20% of startups feature cache nuking. It take a while to blow away 1GB of files on startup. Brian used telemetry to investigate causes for cache purges in bug 774146. Based on this data, Brian will begin tackling what may be the oldest snappy bug so far: bug 105843. For more details on our cache see Nick Hurley’s blog post (also see his link to a similar blog post from a Chrome person).

More Responsive Tabs

Tim Taubert made our new tab animation more pleasant in bug 716108. Tim also landed a fix to halve jank caused by thumbnail capture in bug 774811, this should result in better tab-switching experience. Stay tuned for more developer attention in this area.


Jon Coppeard enabled incremental sweeping: bug 729760. This should result in slightly smaller GC pauses.





  1. The incremental sweeping patch was by Jon Coppeard, not Bill.

  2. SPS is awesome! (I even tweeted that exact statement this week)

    But please please make it do stackwalking on Linux (bug 757186) 🙂

  3. Alon,
    Thanks for spreading the word. We’ll be making SPS(stack unwinding for it) work on 64bit linux as part of making it work on android. Julian Seward is on that.

  4. Awesome stuff. I am eagerly awaiting the tab strip changes and the new theme to land on nightly.


  5. > We’ll be making SPS(stack unwinding for it) work on 64bit linux as part of making it work on android. Julian Seward is on that.

    Great, thanks for the info!

  6. It’s really very good to see this stuff happening. For so long Mozilla’s performance or ‘snappy’ debate – years ago now – was stuck on rants about whether Firefox should have a splash screen and whether Firefox startup wasn’t slow, but only relatively slow because Microsoft ‘cheated’ by pre-loading.

    Keep up the good work.