Bug 17770 – JavaScript execution is dramatically slower while Drosera is attached

• Status: CLOSED
• Resolution: WONTFIX
• Component: New Bugs

[Adam Roben (:aroben)]

JavaScript execution is dramatically slower while Drosera is attached.

It's likely that much of this slowness is due to WebKit making a cross-process call to Drosera for every line of JavaScript executed, even if Drosera has no breakpoints set.

[Adam Roben (:aroben)]

<rdar://problem/5792378>

[Adam Roben (:aroben)]

One possible way we could solve this would be for WebKit to be aware of Drosera's breakpoints and only make cross-process calls when a breakpoint is hit or Drosera requests that we step.

Another possible way to solve this would be to move debugging to be in-process (as covered by bug 17134).

[Adam Roben (:aroben)]

*** Bug 17554 has been marked as a duplicate of this bug. ***

[Adam Roben (:aroben)]

While a lot of the slowness surely comes from the cross-process calls, some of it definitely comes from WebCore/JSC's debugger infrastructure.

Adding a single no-op JavaScriptDebugListener to WebCore's JavaScriptDebugServer caused SunSpider to be 2.42x as slow. Here are the actual results:

Without a JavaScriptDebugListener:

http://webkit.decenturl.com/sunspider-without-javascriptdebuglis

With a JavaScriptDebugListener:

http://webkit.decenturl.com/sunspider-with-a-javascriptdebuglist

[Adam Roben (:aroben)]

I just tried this with Firefox 2 and Firebug. The performance was not significantly different when Firebug was disabled vs. enabled.

Firebug disabled:

http://webkit.decenturl.com/sunspider-without-firebug

Firebug enabled:

http://webkit.decenturl.com/sunspider-with-firebug

[Adam Roben (:aroben)]

Strangely, changing JavaScriptDebugListener to use const KJS::UString& instead of const String& did not improve performance on SunSpider at all, even though it should reduce the number of strings allocated.

[Kevin McCullough]

Drosera is going away and JS debugging is now happening in the WebInspector.

[Timothy Hatcher]

Closing since Drosera has been replaced by the new Web Inspector debugger. Moving to the New Bugs component so the Drosera component can be closed and removed.