Dogfooding Warp

[Jan de Mooij]

Hi all,

The SpiderMonkey (JS) team has been working on a significant update to
our JITs called WarpBuilder (or just Warp) [0,1]. Before we enable
Warp by default in Nightly (hopefully next cycle in 83) we need your
help dogfooding it.

Warp improves performance by reducing the amount of internal type
information that is tracked, optimizing for a broader spectrum of
cases, and by leveraging the same CacheIR optimizations used by last
year’s BaselineInterpreter work [2]. As a result, Warp has a much
simpler design and improves responsiveness and page load performance
significantly (we're seeing 5-15% improvements on many visual metrics
tests). Speedometer is about 10% faster with Warp. The JS engine also
uses less memory when Warp is enabled.

To enable Warp in Nightly:

1. Update to a recent Nightly
2. Go to about:config and set the "javascript.options.warp" pref to true
3. Restart the browser

We're especially interested in stability issues and real-world
performance problems. Warp is currently slower on various synthetic JS
benchmarks such as Octane (which we will continue investigating in the
coming months) but should perform well on web content.

If you find any issues, please file bugs blocking:

https://bugzilla.mozilla.org/show_bug.cgi?id=1613592

If you notice any improvements, we'd love to hear about those too.

Finally, we want to thank our amazing contributors André Bargull and
Tom Schuster for their help implementing and porting many
optimizations.

Turning Warp on is only our first step, and we expect to see a lot of
new optimization work over the next year as we build on this. We are
excited for what the future holds here.

Thanks!
The Warp team

[0] WarpBuilder still utilizes the backend of IonMonkey so we don't
feel it has earned the WarpMonkey name just yet.
[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1613592
[2] https://hacks.mozilla.org/2019/08/the-baseline-interpreter-a-faster-js-interpreter-in-firefox-70/

[Jared Wein (Mozilla)]

Hi Jan,

Thanks for the update and congratulations on reaching this milestone.

Would you like to add Warp to the list of experimental features in
about:preferences? When a feature is listed there, it will appear in crash
stats and about:support, and also give users an easy way to enable/disable.
Feel free to contact me off-list if you are interested. I'm happy to help.

Thanks,
Jared

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--
Jared Wein
Staff Software Engineer, Firefox
Mozilla Corporation

[Jan de Mooij]

Warp is now enabled by default on Nightly, after positive feedback
from users dogfooding it [0,1].

Here are just a few of the Talos/Raptor graphs showing improvements
when Warp landed:

- 20% on Win64 GDocs loadtime: https://mzl.la/3cp6dAs
- 13% on Android Reddit SpeedIndex: https://mzl.la/2RUWdp8
- 18% on pdfpaint: https://mzl.la/2HtXb9W
- 8% on tp6 JS memory: https://mzl.la/3j2VwGb
- 8% on damp (devtools perf): https://mzl.la/3kLbhSM

Please let us know if you notice any improvements or regressions.

Thanks,
The Warp team

[0] https://www.reddit.com/r/firefox/comments/itib6s/dogfooding_warp_on_nightly_new_js_jit_engine/
[1] https://www.reddit.com/r/firefox/comments/iy2036/nightly_is_finally_feeling_as_fast_as_chromium/

[David Teller]

That's an impressive speedup!

Congrats on enabling this, everyone.