On Tue, Feb 18, 2014 at 7:44 AM, Adam Barth <aba...@webkit.org> wrote:
> On Sat, Feb 15, 2014 at 4:07 PM, Ryosuke Niwa <rn...@webkit.org> wrote: > >> Now that we've removed all of the existing shadow DOM implementations >> from trunk in http://trac.webkit.org/changeset/164131, I'm intending to >> work on new web components implementations in a branch based on the >> feedback Apple has given on public-webapps and www-style in near future, >> probably starting with custom elements. >> >> I'd like to implement them in a branch to not inadvertently introduce >> performance regressions. The old implementation on trunk resulted in 5% >> overall slowdown in the page load time but we didn't quantify that until we >> removed the feature entirely last year. That's probably because the >> feature was added over years as a pile of small changesets each of which >> introduced immeasurably small performance regressions. Development in a >> branch allows a faithful performance comparison between the two. >> > > The approach we were successful with in Blink was to restructure how we > construct the render tree. At the time Blink branched from WebKit, the > algorithm we both used to construct the render tree was N^2. The inner > loop of the N^2 algorithm contained more complex DOM traversals due to > shadow DOM. When you profile the code, it looks like shadow DOM is > expensive, but the bigger win is just to remove the N^2 algorithm, which > we've done in Blink. After removing the N^2 algorithm, shadow DOM related > code falls off the profile completely. > Makes sense. I think one big problem with the old implementation was that it started off with a completely different API and feature set and the code had to "evolve" as the spec developed further over years and accumulated design kinks. I'm sure we can avoid introducing O(n^2) algorithms if we started from scratch looking at the latest design. - R. Niwa
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