Updates:
Status: Accepted
Cc: [email protected] [email protected]
Comment #1 on issue 2452 by [email protected]: Array.shift extremely
slow when array has >= 128991 elements
http://code.google.com/p/v8/issues/detail?id=2452
I modified your test to run it in d8:
function time(fn) {
var start = new Date();
fn();
var end = new Date();
print(end - start);
}
[1e3, 1e4, 1e5, 122000, 132000].forEach(function (num) {
var a = new Array(num).join(',').split(',');
print(num);
time(function shiftFn() {
while (a.length) a.shift();
});
});
For me, the break didn't happen at 128991, but somewhat higher, but the
problem remains. A profile without the problematic size looks like this:
2032 9.7% v8::internal::Builtin_ArrayShift
633 3.0% v8::internal::LeftTrimFixedArray
547 2.6% GLIBC_2.0 _IO_vfprintf
522 2.5% v8::internal::Runtime_StringSplit
477 2.3% v8::internal::Factory::NewProperSubString
[...]
which is alright. If I add that 132000 to the list (and abort the run after
only a few seconds), the profile looks wildly different:
286270 48.9% v8::internal::StoreBuffer::Compact()
151530 25.9%
_ZN2v88internalL12MoveElementsEPNS0_4HeapEPNS0_18AssertNoAllocationEPNS0_10FixedArrayEiS6_ii.isra.78.part.79
108651 18.6% _ZN2v88internal11StoreBuffer6FilterEi.constprop.48
[/usr/local/google/home/yangguo/v8/out/ia32.release/d8]
2056 0.4% v8::internal::Builtin_ArrayShift
750 0.1% v8::internal::Runtime_StringSplit
737 0.1% v8::internal::Factory::NewProperSubString
[...]
We seem to lose a lot of time in the store buffer.
Adding the experts for this on CC :)
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