[Webkit-unassigned] [Bug 189558] New: [JSC] Heap::reportExtraMemoryVisited shows contention if we have many JSString

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=189558

            Bug ID: 189558
           Summary: [JSC] Heap::reportExtraMemoryVisited shows contention
                    if we have many JSString
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: yusukesuzuki at slowstart.org

When running web-tooling-benchmark postcss test on Linux JSCOnly port, we get the following result in `perf report`.

  10.95%  AutomaticThread  libJavaScriptCore.so.1.0.0  [.] JSC::Heap::reportExtraMemoryVisited

This is because postcss produces bunch of JSString, which requires reportExtraMemoryVisited calls in visitChildren.
And since reportExtraMemoryVisited attempts to update atomic counter, if we have bunch of marking threads, it just becomes contended!

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