In addition to what Marja said, I assume that a significant difference (even without JIT) is that JavaScript can use Inline Caches, whereas the API cannot.
On Mon, Oct 17, 2022 at 10:34 AM James Chen <[email protected]> wrote: > 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? Thanks. >>> >> -- -- v8-dev mailing list [email protected] http://groups.google.com/group/v8-dev --- You received this message because you are subscribed to the Google Groups "v8-dev" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/v8-dev/CAKSzg3Ssoev-czmjbKJPdCFT_4s4wsZK8PTupu7bs1SwABDOiw%40mail.gmail.com.
