[Webkit-unassigned] [Bug 68440] New: Peak execution time of the JavaScriptCore garbage collector causes pauses that prevent applications running at a constant frame rate.

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=68440

           Summary: Peak execution time of the JavaScriptCore garbage
                    collector causes pauses that prevent applications
                    running at a constant frame rate.
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: UNCONFIRMED
          Severity: Major
          Priority: P2
         Component: JavaScriptCore
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: michaelbraithwaite at turbulenz.com


With JSC from http://trac.webkit.org/browser/releases/WebKitGTK/webkit-1.4.2 on Windows and Mac.

For applications, e.g. games, that require smooth animation a constant frame rate is desired, typically 60hz. 

Running complex JavaScript applications under JavaScriptCore we see various pauses that are caused by Heap::reset(). Putting in some basic timing code shows peak execution time on a Core i5 @3.45Ghz regularly exceed 0.1 seconds and can be up to 0.25s for some titles that have very many objects (Heap.objectCount() ~= 3million).  Breaking this down we see Heap::markRoots() take ~60% of this and MarkedSpace::sweep() the other 40% (when it executes). 

We can work on reducing the number of objects created but the cost is more than 10x 1/60s on a moderately fast CPU and on slower machines, e.g. some laptops, the pauses are obviously much larger. 

I can see in the trunk changes to the heap, e.g. adding some WeakReference code (for generational gc?). Are there other major changes planned to speed things up or reduce the peak cost (split up sweep cost or/and use other threads)?

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