Quantum Flow Engineering Newsletter #18

Ehsan Akhgari ehsan.akhgari at gmail.com
Fri Aug 4 08:04:00 UTC 2017

Hi everyone,

This has been a busy week.  A lot of fixes have landed, setting up the
Firefox 57 cycle for a good start.  On the platform side, a notable change
that will be in the upcoming Nightly is the fix for document.cookie using
synchronous IPC.  This super popular API call slows down various web pages
today in Firefox, and starting from tomorrow, the affected pages should
experience a great speedup.  I have sometimes seen the slowdown caused by
this one issue to amount to a second or more in some situations, thanks a
lot to Amy and Josh for their hard work on this feature.  The readers of
these newsletters know that the work on fixing this issue has gone on for a
long time, and it's great to see it land early in the cycle.

On the front-end side, more and more of the UI changes of Photon are
landing in Nightly.  One of the overall changes that I have seen is that
the interface is starting to feel a lot more responsive and snappy than it
was around this time last year.  This is due to many different details.  A
lot of work has gone into fixing rough edges in the performance of the
existing code, some of which I have covered but most of which is under
the Photon
Performance project <https://bugzilla.mozilla.org/show_bug.cgi?id=1363750>.
Also the new UI is built with performance in mind, so for example where
animations are used, they use the compositor and don't run on the main
thread.  All of the pieces of this performance puzzle are nicely coming to
fit in together, and it is great to see that this hard work is paying off.

On the Speedometer front, things are progressing with fast pace.  We have
been fixing issues that have been on our list from the previous findings,
which has somewhat slowed down the pace of finding new issues to work on.
Although the SpiderMonkey team haven't waited around
<https://bugzilla.mozilla.org/show_bug.cgi?id=1245279> and are continually
finding new optimization opportunities out of further investigations.
There is still more work to be done there!

I will now move own to acknowledge the great work of all of those who
helped make Firefox faster last week.  I hope I am not mistakenly
forgetting any names here!

   - Andrew McCreight got rid of some cycle collector overhead
   <https://bugzilla.mozilla.org/show_bug.cgi?id=1385459> related to using
   QueryInterface to canonicalize the nsISupports pointers stored in the
   purple buffer, and similarly for pointers encountered during traversal
   of native roots <https://bugzilla.mozilla.org/show_bug.cgi?id=1385474>
   as well.
   - Kris Maglione added some utilities to BrowserUtils
   <https://bugzilla.mozilla.org/show_bug.cgi?id=1383367> that should help
   our front-end devs avoid synchronous layout and style flushes.
   - Amy Chung got rid of the sync IPC messages in the cookie service
   <https://bugzilla.mozilla.org/show_bug.cgi?id=1331680>! This was a
   substantial amount of work and should eliminate jank on a number of sites
   that get and set cookies frequently.
   - Jessica Jong made us check a boolean flag instead of doing a linear
   search looking for an attribute in order to determine whether an Element is
   required <https://bugzilla.mozilla.org/show_bug.cgi?id=1385478>.
   - André Bargull made String.prototype.toLower/UpperCase use direct VM
   calls, and also added specialized unicode::CanLower/UpperCase overloads for
   Latin1 characters <https://bugzilla.mozilla.org/show_bug.cgi?id=1383647>.
   He also added an Ion-inline path for Reflect.getPrototypeOf()
   <https://bugzilla.mozilla.org/show_bug.cgi?id=1385802>.  Additionally,
   he made it possible to inline UnsafeGetReservedSlot when the object is
   typed as MIRType::Value
   <https://bugzilla.mozilla.org/show_bug.cgi?id=1383645>.  Last but not
   least, he inlined ToObject when called with MIRType::Value
   - Mike Conley ported scrollbox to use smooth scrolling instead of JS
   driven scrolling <https://bugzilla.mozilla.org/show_bug.cgi?id=1356705>.
   This affects most importantly scrolling the tab bar, and should make it
   more smooth by removing a lot of slow code that used to run and off-loading
   that work to the compositor through CSS-based smooth scrolling!  He notes
   <https://bugzilla.mozilla.org/show_bug.cgi?id=1356705#c67> on the bug
   that in order to achieve great performance some follow-ups may be needed.
   - Olli Pettay avoided allocating element state objects needlessly when
   saving the state of <input> and <select> elements
   - Tim Taubert and Michael Layzell collaborated on reducing the cost of
   the FormDataListener event handler
   <https://bugzilla.mozilla.org/show_bug.cgi?id=1373672> inside
   - C.J. Ku fine tuned nsDisplaySVGText::Paint() in several ways
   - Tom Schuster optimized String.prototype.indexOf/lastIndexOf for the
   case where the search string is equal to the string itself
   - Tooru Fujisawa improved the inlining of RegExpMatcher, RegExpSearcher
   and RegExpTester <https://bugzilla.mozilla.org/show_bug.cgi?id=1366263>
   in IonMonkey.
   - Nicholas Hurley ensured HTTP/2 pushes get canceled if they are already
   in the cache <https://bugzilla.mozilla.org/show_bug.cgi?id=1367551>.
   - Jerry Shih deferred initializing some part of the platform font list
   to the idle queue <https://bugzilla.mozilla.org/show_bug.cgi?id=1368531>.
   - Felipe Gomes updated the transitionend properties of <option> elements
   used to implement <select> drop-downs in e10s mode in a deferred task

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