Trying to get normalized CPU usage for node process

Question

I'm trying to calculate the normalized cpu percentage for my node process. My goal is to get it to match the output that I have in my htop for the pid but I'm unable to do so. My code is below along with my htop output.

import { cpuUsage } from "node:process";
import { cpus } from "os";

function basicCpuUsage() {
  const startTime = process.hrtime();
  const startUsage = cpuUsage();
  const numCpus = cpus().length;

  const add = 1 + 1; // make cpu do work?

  const usageDiff = cpuUsage(startUsage); // get diff time from start
  const endTime = process.hrtime(startTime); // total amount of time that has elapsed
  const usageMS = (usageDiff.user + usageDiff.system) / 1e3;
  const totalMS = endTime[0] * 1e3 + endTime[1] / 1e6;

  const cpuPercent = (usageMS / totalMS) * 100;
  const normTotal = usageMS / numCpus; // average usage time per cpu
  const normPercent = (normTotal / totalMS) * 100;

  console.log({
    cpuPercent: cpuPercent.toFixed(2),
    normPercent: normPercent.toFixed(2),
  });
}

process.title = "CPU Test";
const { pid } = process;
console.log({ pid });
const title = setInterval(() => {
  basicCpuUsage();
}, 1000);

Here is my output, as you can see my code cpu output does no match my htop cpu output. Which part of my calculation is incorrect? I was thinking this might have to do with my setInterval function call, but not sure. I am attempting to create a long running process where I can view the cpu usage.

Answer 1

Turns out I was making an incorrect calculation. I was dividing my totalTimeMS twice when I should have done it once. Additionally I moved the currentUsage and currentTime to the outside of the function.

Below is the correct calculation:

import { cpus } from "os";

let currentUsage = process.cpuUsage();
let currentTime = process.hrtime();

function basicCpuUsage() {
  const numCpus = cpus().length;

  const usageDiff = process.cpuUsage(currentUsage); // get diff time from start
  const endTime = process.hrtime(currentTime); // total amount of time that has elapsed

  currentUsage = process.cpuUsage()
  currentTime = process.hrtime();

  const usageMS = (usageDiff.user + usageDiff.system) / 1e3;
  const totalMS = endTime[0] * 1e3 + endTime[1] / 1e6;

  const cpuPercent = (usageMS / totalMS) * 100;
  const normPercent = (usageMS / totalMS / numCpus) * 100; // average usage time per cpu

  console.log({
    cpuPercent: cpuPercent.toFixed(2),
    normPercent: normPercent.toFixed(2),
  });
}

process.title = "CPU Test";

setInterval(() => {
 for (let i = 0; i < 25; i++) {
    const add = 1 + 1;
  }
  basicCpuUsage();
}, 5000);