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Math within vm context is extremely slow #49283
Description
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
Activity
bnoordhuis commentedon Aug 22, 2023
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 commentedon Aug 22, 2023
@bnoordhuis, Thanks for the explanation, but I'm not agree with "wontfix".
a-parser commentedon Aug 22, 2023
there is a workaround by localizing Math
but honestly it's looks ugly
a-parser commentedon Aug 22, 2023
related #30709
bnoordhuis commentedon Aug 23, 2023
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.