[Webkit-unassigned] [Bug 81865] New: Improve our style sharing algorithm parameters

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=81865

           Summary: Improve our style sharing algorithm parameters
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: jchaffraix at webkit.org
                CC: koivisto at iki.fi, kling at webkit.org


Currently our style sharing algorithm uses those 2 values that I set a year ago:

static const unsigned cStyleSearchThreshold = 10;
static const unsigned cStyleSearchLevelThreshold = 10;

Those were set up to improve style sharing and instrumenting our style sharing, I don't think they are an optimum of performance vs memory savings.

My current discovery so far based on html5-full-render.html and moz, intl1, intl2 and alexa_us page cyclers:
* Our current style sharing rate is 28.6% (that is out of 1000 calls to locateSharedStyle, 286 returns a match)
* Most of the tree walking leads to bailing out without having a shared style (95% of the "budget" used by the algorithm (|count| and |visitedNode| in locateSharedStyle) fails |sharedNode| NULL-check)
* Overall, when styles are shared, we don't walk the tree that much (on average, |count| is around 1 and |visitedCount| is around 1 too).

What I am missing is the distribution of the parameters to know what would be an optimum.

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