Math within vm context is extremely slow

[a-parser]

Version

14.x,16.x,18.x,20.x

Platform

linux/macos

Subsystem

No response

What steps will reproduce the bug?

Accessing to Math within vm context is about x50-x100 slower vs native execution:

native 0.287
context 18.947
context-builtin-pow 0.292

const vm = require('vm');

function math_benchmark(name, builtinPow = false) {
    const startTime = Date.now();
    for(let i = 1; i <= 100_000_000; i++) {
        let x = builtinPow ? i ** 2 : Math.pow(i, 2);
        if(i % 100_000_000 == 0) {
            x && console.log(name, (Date.now() - startTime) / 1000);
        }
    }
}

math_benchmark('native');

const ctx = {console};
ctx.global = ctx;
vm.createContext(ctx);

vm.runInNewContext(`
    ${math_benchmark.toString()}
    math_benchmark("context")
`, ctx);

vm.runInNewContext(`
    ${math_benchmark.toString()}
    math_benchmark("context-builtin-pow", true)
`, ctx);

How often does it reproduce? Is there a required condition?

always, tested on all node versions from 14 to 20

What is the expected behavior? Why is that the expected behavior?

it's expected to have nearly same performance

What do you see instead?

it's slower x50-x100 times

Additional information

No response

[bnoordhuis]

Thanks for the report but the slowdown isn't unexpected, it's an inevitable consequence of how the vm module is implemented.

Executive summary: V8 can normally inline and optimize Math method calls but the vm module intercepts all loads and stores from/to the global object, depriving V8 of the possibility of recognizing such built-in methods.

It's why I wrote the vime module years ago, it doesn't suffer from that defect. Closing as a wontfix/cantfix.

[a-parser]

@bnoordhuis, Thanks for the explanation, but I'm not agree with "wontfix".

1. This performance behavior completely undocumented in vm module docs
2. Math is JavaScript builtin object, seems it not need to be proxied within vm module

[a-parser]

there is a workaround by localizing Math

function math_benchmark(name, builtinPow = false) {
    const startTime = Date.now();

    const Math = global.Math;
    for(let i = 1; i <= 100_000_000; i++) {
        let x = builtinPow ? i ** 2 : Math.pow(i, 2);
        if(i % 100_000_000 == 0) {
            x && console.log(name, (Date.now() - startTime) / 1000);
        }
    }
}

but honestly it's looks ugly

[a-parser]

related #30709

[bnoordhuis]

Math is JavaScript builtin object, seems it not need to be proxied within vm module

That's how V8's API works, it's all or nothing. If you feel the documentation is lacking, go ahead and send a pull request.