Thanks for your answer,
i was just curious about the performance impact with the debugger
because of this pdf:
http://www.daimi.au.dk/~amoeller/VM/Debugging_support_in_V8.pdf
In Page 6 theres a design criteria: No speed degrading when debugging
anyway here's a minimal example showing my issue:
var BreakPointPerformance = function() {
}
BreakPointPerformance.prototype.breakFunc = function() {
return 0;
}
BreakPointPerformance.prototype.mathFunc = function() {
var a = Math.sqrt(Math.random());
return a;
}
BreakPointPerformance.prototype.runLoop = function() {
console.time("loop time");
var b = 0;
for(var i=0;i<10000000;i++) {
b+=this.mathFunc();
}
console.timeEnd("loop time");
}
var p = new BreakPointPerformance();
p.runLoop();
On my Machine running Chrome the function takes 100ms to execute.
If i set a breakpoint at the return statement of breakFunc, which is
not executed at all,
i get around 19000ms.
I also get these 19000ms if the breakpoint is set, but disabled (if i
remember correctly this has been posted as issue already).
Why is the execution so slow even if breakFunc isn't executed?
kind regards,
Martin
On 12 Jun., 08:12, Yang Guo <[email protected]> wrote:
> Hi Martin,
>
> this is a known fact. Performance critical code usually get a second
> treatment with the optimizing compiler after it has been run for a short
> while. When a breakpoint is set inside a function, it is deoptimized to
> enable breaking and debugging. This can have a big performance impact. This
> is a conscious design decision: we do not require code that is being
> debugged to run fast.
>
> However, if you can provide a pure javascript (running on V8's dev shell,
> D8, alone) sample, I can take a look and see if there is something unusual
> going on.
>
> Regards,
>
> Yang
>
>
>
>
>
>
>
> On Mon, Jun 11, 2012 at 11:09 PM, Martin <[email protected]> wrote:
> > Hello,
>
> > the following applies to both Chrome 19.0.1084.52 m using the
> > Developer Tools and Node.js 0.7.6 pre using node-inspector as Debug
> > Frontend.
> > I've noticed that setting a breakpoint (in frequently executed code),
> > no matter if the breakpoint is conditional or not slows down the
> > execution of javascript significally.
> > The function i'm trying to debug takes around 2 seconds to execute
> > without breakpoints.
> > If i set a breakpoint i stopped waiting for the end of execution (or
> > actually hitting the breakpoint) after 10 minutes!
> > Is this a known issue?
> > I haven't found anything related in the issue tracker.
>
> > Recently i debugged a webworker, setting a breakpoint in a function
> > which was not executed at all, but the behaviour was the same:
> > javascript execution slowed down alot.
>
> > kind regards
> > Martin
>
> > --
> > v8-dev mailing list
> > [email protected]
> >http://groups.google.com/group/v8-dev
--
v8-dev mailing list
[email protected]
http://groups.google.com/group/v8-dev
