Bug 100873 - REGRESSION (r132941): attribute modification 10% performance regression
Summary: REGRESSION (r132941): attribute modification 10% performance regression
Status: RESOLVED FIXED
Alias: None
Product: WebKit
Classification: Unclassified
Component: HTML DOM (show other bugs)
Version: 528+ (Nightly build)
Hardware: Unspecified Unspecified
: P2 Normal
Assignee: Nobody
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2012-10-31 11:41 PDT by Ojan Vafai
Modified: 2012-11-01 18:12 PDT (History)
9 users (show)

See Also:

Attachments
patch (10.50 KB, patch)
2012-11-01 10:50 PDT, Antti Koivisto 		ojan: review+
webkit.review.bot: commit-queue-
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Comment 2 Andreas Kling 2012-10-31 12:04:06 PDT 
If it was http://trac.webkit.org/changeset/132941, I think http://trac.webkit.org/changeset/133021 should fix it.
Comment 3 Ojan Vafai 2012-10-31 12:48:18 PDT 
(In reply to comment #2)
> If it was http://trac.webkit.org/changeset/132941, I think http://trac.webkit.org/changeset/133021 should fix it.

133021 did not fix it.
Comment 4 Antti Koivisto 2012-10-31 12:51:39 PDT 
Not sure it will. We'll see. I think a sufficiently artificial test case might see a regression from that change. There are ways to improve if needed.
Comment 5 Antti Koivisto 2012-10-31 13:10:35 PDT 
Turns out the difference finding algorithm using SpaceSplitString mutation is too slow:

Running Time	Self		Symbol Name
1714.0ms    5.6%	302,0	 	 WebCore::Element::classAttributeChanged(WTF::AtomicString const&)
532.0ms    1.7%	174,0	 	  WebCore::SpaceSplitString::remove(WTF::AtomicString const&)
277.0ms    0.9%	66,0	 	   WebCore::SpaceSplitString::ensureUnique()
136.0ms    0.4%	136,0	 	    WTF::fastMalloc(unsigned long)
75.0ms    0.2%	75,0	 	    WTF::Vector<WTF::AtomicString, 4ul>::Vector(WTF::Vector<WTF::AtomicString, 4ul> const&)

Should be easy to optimize this away.
Comment 6 Antti Koivisto 2012-11-01 10:50:51 PDT 
Created attachment 171893 [details]
patch
Comment 7 Ojan Vafai 2012-11-01 11:31:40 PDT 
Comment on attachment 171893 [details]
patch

View in context: https://bugs.webkit.org/attachment.cgi?id=171893&action=review

> Source/WebCore/dom/Element.cpp:723
> +    StyleResolver* styleResolver = document()->styleResolverIfExists();
> +    bool testShouldInvalidateStyle = attached() && styleResolver && styleChangeType() < FullStyleChange;

I almost wonder if it's worth adding a static helper function here since this code is duplicated with Element::classAttributeChanged.

static StyleResolver* styleResolverForTestingStyleInvalidation(Document* document, Element* element)
{
    if (!element->attached() || element->needsStyleRecalc() || styleTypeChange >= FullStyleChange)
        return 0;
    return document()->styleResolverIfExists();
}

Then you wouldn't need the testShouldInvalidateStyle at all and could just null check the returned style resolver.

It's not clearly better to me, but it does avoid some duplication. Up to you.

> Source/WebCore/dom/Element.cpp:733
> +            if (shouldInvalidateStyle)
> +                testShouldInvalidateStyle = false;

I think you could avoid needing to do this if you put the check below into an else clause. That'd simplify the logic some I think.

} else {
    if (name == HTMLNames::nameAttr)
        setHasName(!newValue.isNull());
    shouldInvalidateStyle = ...;
}

> Source/WebCore/dom/Element.cpp:738
> +    shouldInvalidateStyle = testShouldInvalidateStyle && styleResolver->hasSelectorForAttribute(name.localName());

Not sure it matters, but we currently only do this if (!needsStyleRecalc()). Maybe testShouldInvalidateStyle should also && !needsStyleRecalc()? Obviously the same would apply in Element::classAttributeChanged. Saves a hashtable lookup. Not sure it matters in practice.
Comment 8 Antti Koivisto 2012-11-01 11:45:05 PDT 
(In reply to comment #7)
> Not sure it matters, but we currently only do this if (!needsStyleRecalc()). Maybe testShouldInvalidateStyle should also && !needsStyleRecalc()? Obviously the same would apply in Element::classAttributeChanged. Saves a hashtable lookup. Not sure it matters in practice.

styleChangeType() < FullStyleChange is the equivalent test (more correct in fact).
Comment 9 Ojan Vafai 2012-11-01 11:54:38 PDT 
(In reply to comment #8)
> styleChangeType() < FullStyleChange is the equivalent test (more correct in fact).

Ah. Got it.
Comment 10 WebKit Review Bot 2012-11-01 12:07:39 PDT 
Comment on attachment 171893 [details]
patch

Attachment 171893 [details] did not pass chromium-ews (chromium-xvfb):
Output: http://queues.webkit.org/results/14686598

New failing tests:
css3/viewport-percentage-lengths/css3-viewport-percentage-lengths-getStyle.html
fast/dynamic/004.html
Comment 11 Antti Koivisto 2012-11-01 12:41:53 PDT 
http://trac.webkit.org/changeset/133214 (with the test breaking bug fixed)
Comment 12 Antti Koivisto 2012-11-01 12:42:13 PDT 
Lets see what the bots say.
Comment 14 Ojan Vafai 2012-11-01 18:12:01 PDT 
Yup. Looks great!