Project Dory

Project Goals

• Investigate the usage of current preferences:
  • Understand and document existing preferences (lifetime, type, whether they are still in use, etc.)
  • Clean up preferences (unused, incorrectly used, non-obvious).
• Use preferences as performance tuning knobs and investigate the performance implications of these knobs.
  • Prioritize the preferences with their relevance to performance.
  • Tweak the preferences and run automated tests against the values to see their performance implications.

Participants

• Kan-Ru Chen
• Cervantes Yu
• Will Wang
• WeiCheng Pan
• Shako Ho
• Walter Chen
• Askeing Yen

Roadmap

• Find a systematic way to manage and prioritize default preference values.
  • Co-work with libpref redesign project on new persistence format of preferences.
  • Find performance related preferences during the process.
  • Get feedback from relevant teams.
    • Initially we may target JS related preferences.
  • Record the performance implications of preferences using the new persistence format.

Things to Consider

• What's the new persistence format for preferences?
• What data should a pref contain?
  • Internal name, a more descriptive name, description, default value, etc.
• #include from smaller subsets in the final pref file.
  • Group prefs that are relevant (sharing the same prefix) in smaller files.
• Standalone top branch indicates that the pref should be under some other branch.
  • There is only 1 pref beginning with "slider": slider.snapMultiplier
  • Move to browser.slider.snapMultiplier?
• camelCase, underscore_names, or dashed-names?
• Envisioning a front-end user interface that is more user-friendly than about:config?
  • Makes it easier for users to tweak or experiment with the browser.
• Inline readonly prefs in code as constants?

Results

• A Hasal trial run to test the performance effect of changing JS baseline JIT threshold values:
  • https://gist.github.com/ShakoHo/2e2321294d567d913eea5eaa58af60e0
  • Twiddling the preference has influence of performance as can be seen in the test results, but there is no consistent change among the tests.

Preference Name	Gist URL
network.buffer.cache.size	https://gist.github.com/0ffacfb61ce17a730df6cb2f18fa1483
network.http.spdy.chunk-size	https://gist.github.com/0ef99bb241f8de7392b592c34a605b3b
javascript.options.baselinejit.threshold	https://gist.github.com/6b2ffc3dfcdab7872c11116c79a7ad0e
javascript.options.ion.threshold	https://gist.github.com/ddf16cb123c5296cf3ca4a69a2ba6cf8
network.predictor.preconnect-min-confidence	https://gist.github.com/72dae79449b55d14e1e3a5dc67121a7f
layout.display-list.retain	https://gist.github.com/cfafaa3b88f3e0ce55dc091e3ac5190d
network.tcp.sendbuffer	https://gist.github.com/c89ed6ea370df9b67371966ff5c52a41
network.http.speculative-parallel-limit	https://gist.github.com/18f72b4c30ec552cdb7cf17cce8febaa
layers.tile-width	https://gist.github.com/6e283306aad2113c8196b5d57201ba18
network.http.spdy.default-concurrent	https://gist.github.com/4118e79b7a7ce3982747912913323130
dom.idle_period.throttled_length	https://gist.github.com/f2d0285587888c42a36bdecda967c4ee
layers.tile-height	https://gist.github.com/4e82e980238c740e4e9dd41e729c0e9f
network.http.max-persistent-connections-per-server	https://gist.github.com/8994e522a9eb6dc4f7fe1c79320bd215
network.buffer.cache.count	https://gist.github.com/7c8b2ca0d987f0ed6897695c35a55095

• Test result summary
  • javascript.options.baselinejit.threshold: for most test cases that completes quickly (< 100 ms), the default value performs similarly to the other values. Setting it to 50 is likely to have a smaller variation. For test cases that take longer time (> 200 ms) Setting the pref to 50 almost outperforms the default value. The only exception is test 'test_firefox_gslide_ail_pagedown_0', but the difference is marginal (within 1 frame).