Got it. I would modify my test code to see whether the result could get better.
Thanks for your reply. :) 在2022年10月17日星期一 UTC+8 13:59:35<[email protected]> 写道： > 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 <[email protected]> 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? 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