Changeset 80861 in webkit

Timestamp:

Mar 11, 2011 10:29:31 AM (13 years ago)

Author:

tonyg@chromium.org

Message:

2011-03-11 Tony Gentilcore <​tonyg@chromium.org>

Reviewed by Eric Seidel.

Let the parser yield for layout before running scripts
​https://bugs.webkit.org/show_bug.cgi?id=54355

Prior to this patch, the parser would yield to perform a layout/paint before running a
script only if the script or a stylesheet blocking the script is not loaded yet. Since we
don't preload scan into the body while parsing the head, typically we'll block on a script
early in the body that causes us to yield to do the first paint within a reasonable time.

However, I'm planning to change the PreloadScanner to scan into the body from the head.
That significantly improves overall load time, but would hurt first paint time because
fewer scripts would be blocked during parsing and thus wouldn't yield.

This change causes us to yield before running scripts if we haven't painted yet (regardless
of whether or not the script is loaded). In addition to allowing the above mentioned
PreloadScanner change to be implemented without regressing first paint time, this also
improves first paint time by itself.

I tested Alexa's top 45 websites using Web Page Replay to control the content and simulate
bandwidth. This patch improved average first paint time by 1% over an unlimited connection,
6% over a 1Mbps connection and 11% over a 5Mbps connection. There was no statistically
signifcant change in page load time.

Within the pages tested, 33 had no statistically significant change in time to first paint,
12 improved, and none regressed. Of the improved, some of the standouts from the 1Mbps set
are: 20% on youtube, 37% on wiki, 27% on ebay, 13% on cnn, 16% on espn, 74% on sohu.

• html/parser/HTMLDocumentParser.cpp: (WebCore::HTMLDocumentParser::canTakeNextToken): This is the new yield point. (WebCore::HTMLDocumentParser::pumpTokenizer): Remove ASSERT that we are not paused. isPaused means that we are waiting for a script. Bug 54574 changed pumpTokenizer() so that it does the right thing whether we are just before a token or waiting for a script. Now that we may yield before a token or before a script, this may be called while paused.
• html/parser/HTMLParserScheduler.cpp: (WebCore::HTMLParserScheduler::checkForYieldBeforeScript): Added.
• page/FrameView.h: (WebCore::FrameView::hasEverPainted): Added.

Location:

trunk/Source/WebCore

Files:

• ChangeLog (modified) (1 diff)
• html/parser/HTMLDocumentParser.cpp (modified) (2 diffs)
• html/parser/HTMLParserScheduler.cpp (modified) (1 diff)
• html/parser/HTMLParserScheduler.h (modified) (1 diff)
• page/FrameView.h (modified) (1 diff)

trunk/Source/WebCore/ChangeLog

@@ +1 @@
+2011-03-11  Tony Gentilcore  <tonyg@chromium.org>
+
+        Reviewed by Eric Seidel.
+
+        Let the parser yield for layout before running scripts
+        https://bugs.webkit.org/show_bug.cgi?id=54355
+
+        Prior to this patch, the parser would yield to perform a layout/paint before running a
+        script only if the script or a stylesheet blocking the script is not loaded yet. Since we
+        don't preload scan into the body while parsing the head, typically we'll block on a script
+        early in the body that causes us to yield to do the first paint within a reasonable time.
+
+        However, I'm planning to change the PreloadScanner to scan into the body from the head.
+        That significantly improves overall load time, but would hurt first paint time because
+        fewer scripts would be blocked during parsing and thus wouldn't yield.
+
+        This change causes us to yield before running scripts if we haven't painted yet (regardless
+        of whether or not the script is loaded). In addition to allowing the above mentioned
+        PreloadScanner change to be implemented without regressing first paint time, this also
+        improves first paint time by itself.
+
+        I tested Alexa's top 45 websites using Web Page Replay to control the content and simulate
+        bandwidth. This patch improved average first paint time by 1% over an unlimited connection,
+        6% over a 1Mbps connection and 11% over a 5Mbps connection. There was no statistically
+        signifcant change in page load time.
+
+        Within the pages tested, 33 had no statistically significant change in time to first paint,
+        12 improved, and none regressed. Of the improved, some of the standouts from the 1Mbps set
+        are: 20% on youtube, 37% on wiki, 27% on ebay, 13% on cnn, 16% on espn, 74% on sohu.
+
+        * html/parser/HTMLDocumentParser.cpp:
+        (WebCore::HTMLDocumentParser::canTakeNextToken): This is the new yield point.
+        (WebCore::HTMLDocumentParser::pumpTokenizer): Remove ASSERT that we are not paused. isPaused
+        means that we are waiting for a script. Bug 54574 changed pumpTokenizer() so that it does
+        the right thing whether we are just before a token or waiting for a script. Now that we may
+        yield before a token or before a script, this may be called while paused.
+        * html/parser/HTMLParserScheduler.cpp:
+        (WebCore::HTMLParserScheduler::checkForYieldBeforeScript): Added.
+        * page/FrameView.h:
+        (WebCore::FrameView::hasEverPainted): Added.
+
 2011-03-11  Dimitri Glazkov  <dglazkov@chromium.org>
 

trunk/Source/WebCore/html/parser/HTMLDocumentParser.cpp

@@ -213 +213 @@
     // The parser will pause itself when waiting on a script to load or run.
     if (m_treeBuilder->isPaused()) {
+        if (mode == AllowYield)
+            m_parserScheduler->checkForYieldBeforeScript(session);
+
+        // If we don't run the script, we cannot allow the next token to be taken.
+        if (session.needsYield)
+            return false;
+
         // If we're paused waiting for a script, we try to execute scripts before continuing.
         bool shouldContinueParsing = runScriptsForPausedTreeBuilder();
@@ -239 +246 @@
 {
     ASSERT(!isStopped());
-    ASSERT(!m_treeBuilder->isPaused());
     ASSERT(!isScheduledForResume());
     // ASSERT that this object is both attached to the Document and protected.

trunk/Source/WebCore/html/parser/HTMLParserScheduler.cpp

@@ -87 +87 @@
 }
 
+void HTMLParserScheduler::checkForYieldBeforeScript(PumpSession& session)
+{
+    // If we've never painted before and a layout is pending, yield prior to running
+    // scripts to give the page a chance to paint earlier.
+    Document* document = m_parser->document();
+    bool needsFirstPaint = document->view() && !document->view()->hasEverPainted();
+    if (needsFirstPaint && document->isLayoutTimerActive())
+        session.needsYield = true;
+}
+
 void HTMLParserScheduler::scheduleForResume()
 {

trunk/Source/WebCore/html/parser/HTMLParserScheduler.h

@@ -71 +71 @@
         ++session.processedTokens;
     }
+    void checkForYieldBeforeScript(PumpSession&);
 
     void scheduleForResume();

trunk/Source/WebCore/page/FrameView.h

@@ -207 +207 @@
     PaintBehavior paintBehavior() const;
     bool isPainting() const;
+    bool hasEverPainted() const { return m_lastPaintTime; }
     void setNodeToDraw(Node*);