[Webkit-unassigned] [Bug 86165] New: HTML parser should yield more to improve perceived page load time

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=86165

           Summary: HTML parser should yield more to improve perceived
                    page load time
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Keywords: Performance
          Severity: Normal
          Priority: P2
         Component: WebCore Misc.
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: tonyg at chromium.org
                CC: koivisto at iki.fi, abarth at webkit.org,
                    simonjam at chromium.org, mihaip at chromium.org,
                    sullivan at chromium.org


Created an attachment (id=141305)
 --> (https://bugs.webkit.org/attachment.cgi?id=141305&action=review)
Testcase

The HTML parser has heuristics to yield to the event loop. Mihai P pointed out:
> Based on HTMLParserScheduler::checkForYieldBeforeToken it will yield after 4096 tokens _and_ at least 0.5 seconds have passed.
> There is also HTMLParserScheduler::checkForYieldBeforeScript which makes sure we paint at least once before running scripts.

The attached test case demonstrates 5 separate inline script blocks which each take 1s to execute. Sometimes we'll yield after the first, but we always lock the main thread after that (presumably until 4,096 tokens are reached) . Locking the main thread is bad for obvious reasons (can't paint, schedule resource loads, etc). This example isn't completely contrived, it bit a popular Google property.

I propose we change the logic so that if .5 seconds have passed we always schedule a yield for after the next token is parsed. This will avoid the user ever staring at a blank page for too long. Thoughts? Other heuristic ideas?

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