Hi,
I didn't have a deep look, but your benchmarking might not be
representative.
1) V8 probably optimizes such a tight loop a lot (in the JIT mode). You're
using string constants as property names, and V8 sees the whole object
creation code at once, and can generate better optimized code. When we only
need to do one v8::Object::Set, we can't do the same optimizations. (Very
hand-wavy explanation; I didn't look at the actual generated code in this
case.) If you make the object shape and property names + values more
unpredictable (also if you make the benchmark closer to what your actual
deserializer does), you might see a smaller difference. You'll also need to
take into account the time needed for V8 to parse + compile the code, not
only the JS execution time.
2) The string creation (for the property names) is done when we parse the
JS code, so it's outside your benchmark timer. In your C++ version, I
assume it's inside your benchmark timer.
The "16 times faster in the non-JIT mode" is a bit high though, I would've
guessed the difference would be smaller.
Cheers,
On Mon, Oct 17, 2022 at 4:12 AM James Chen <dumgan...@gmail.com> wrote:
> Hello V8 team, thanks for making V8 engine which could run JavaScript
> super fast.
>
> Recently, I want to improve the performance of deserialization for Cocos
> Creator game engine.
>
> Cocos Creator uses V8 for its default JavaScript engine and benefited from
> V8's high performance. There're many classes implemented in JS and some
> implemented in C++. And there will be more and more JS code moved to C++
> side.
>
> I thought about deserializing game assets directly in C++ rather than in
> JS to get better performance since I think C++ code should be faster.
>
> Therefore, I wrote a testcase to test whether we could get benefited from
> C++ code. But unfortunately, I got a really bad result saying that create
> JS object and setting properties in C++ by V8 API is really slower than
> doing that in JS. It's about 50 times slower, in another word, JS execution
> is really fast.
>
> I debugged a little bit and found that the most heavy cost is in
> v8::Object::Set and v8::String::NewFromUtf8.
>
> Part of JS test code:
> const testArr = new Array<MySerializationTestClass>(this.loopCount);
> const start = performance.now();
>
> for (let i = 0; i < this.loopCount; ++i) {
> const test = new MySerializationTestClass();
> testArr[i] = test;
>
> test['booleanValue'] = false;
> test['nullValue'] = null;
> test['undefinedValue'] = undefined;
> test['numberValue0'] = 100.123;
> test['numberValue1'] = 230.2345;
> test['numberValue2'] = 330.2345;
> test['numberValue3'] = 430.2345;
> test['numberValue4'] = 530.2345;
>
> test['stringValue0'] = 'hello 0';
>
> test['stringValue1'] = 'hello 1';
>
> The logic of CPP test code is the same as which in the above JS test code.
> The difference is that we use v8::Object::Set API.
>
> ### JIT Enabled
>
> Cpp code is 55 times slower than JS code.
>
> ### JIT Disabled
>
> Cpp code is 16 times slower than JS code.
>
>
> ### Xcode Profile
>
>
> `v8::Maybe<bool> ret =
> _obj.handle(__isolate)->Set(__isolate->GetCurrentContext(),
> nameValue.ToLocalChecked(), value);` and `v8::String::NewFromUtf8` are the
> main hotspots.
>
> ### What I guess
>
> I guess running JS code directly could make use of the optimization by V8
> Bytecode and JIT by TurboFan. But invoking V8 C++ API will not get the
> optimization.
>
>
> Could you point me out that whether my guess is correct or not? Also, is
> there a better V8 API for setting property? Thanks.
>
>
>
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