613595 - Speed up getElementsByTagName cache hits

Status: RESOLVED FIXED

(Core :: DOM: Core & HTML, defect, P1)

Description

[Boris Zbarsky [:bzbarsky]]

Right now, for getElementsByTagName, we end up atomizing, lowercasing, and atomizing again all before we do our cache check.  That's a total of one lowercasing and three hashtable lookups, in the best case.

Patch coming up that just makes us use the input string to do the hashtable lookup in the cache, and only atomize after that on a miss.  That makes the best-case scenario a single hashtable lookup, period.

This speeds up the dom-query dromaeo tests overall number by 15% or so; the win is all on the getElementsByTagName tests, of course.

Comment 1

[Boris Zbarsky [:bzbarsky]]

Attachment: Speed up the cache-hit case for getElementsByTagName.

Comment 2

[Peter Van der Beken [:peterv]]

Comment on attachment 491936 [details] [diff] [review]
Speed up the cache-hit case for getElementsByTagName.

>diff --git a/content/base/src/nsContentList.h b/content/base/src/nsContentList.h

>+  PRBool MatchesKey(const nsContentListKey& aKey) const {

Nit: I think local style puts { on its own line here.

>+// If aMatchNameSpaceId is kNameSpaceID_Unknown, this will return a
>+// content list which matches ASCIIToLower(aTagname) against HTML
>+// elements in HTML documents and aString against everything else.
>+// For any other value of aMatchNameSpaceId, the list will match
>+// aString against all elements.

s/aString/aTagname/

> already_AddRefed<nsContentList>
> NS_GetContentList(nsINode* aRootNode,
>                   PRInt32 aMatchNameSpaceId,
>-                  nsIAtom* aHTMLMatchAtom,
>-                  nsIAtom* aXMLMatchAtom = nsnull);
>+                  const nsAString& aTagname);

Comment 3

[Boris Zbarsky [:bzbarsky]]

Attachment: Updated to comments

Comment 4

[Boris Zbarsky [:bzbarsky]]

Comment on attachment 492714 [details] [diff] [review]
Updated to comments

Requesting approval.  This is a very safe perf win.

Comment 5

[(no longer active)]

http://hg.mozilla.org/projects/cedar/rev/17d2910e2941

Comment 6

[(no longer active)]

http://hg.mozilla.org/mozilla-central/rev/17d2910e2941