Intensive webview cause app's cpu drop down

Question

I am a front-end developer and I want to monitor webview performance. I have two scenarios:

1. Use deeplink to jump directly to my webview page
2. Use pidof MY_PACKAGE_NAME to get process id
3. Monitor app's main process's cpu by top( previously ps, but apparently top is more appropriate )
4. Inject or not an endless loop using javascript inside webview
5. Cancel the endless loop and calculate the average cpu percentage

The result shows the endless loop case's avg cpu is lower than the no loop one.

This is counter-intuitive, I understand that modern app has multi-process structure, but why on earth endless loop's case has lower cpu.

I am using playwright to connect and send adb command to communicate with my android device. Below is the result:

{
  "loop": {
    "avg": 25.7,
    "p25": 0,
    "p50": 3.5,
    "p75": 21.2,
    "p80": 65.2,
    "p90": 92.8,
    "p95": 99.8,
    "p99": 190.8,
    "max": 306
  },
  "no-loop": {
    "avg": 13.3,
    "p25": 0,
    "p50": 3.4,
    "p75": 7.1,
    "p80": 10.3,
    "p90": 21,
    "p95": 81.3,
    "p99": 195.6,
    "max": 274
  }
}

For those interested in source code, below's the source code written in typescript.

import { _android as android } from "playwright";

const [device] = await android.devices();

await device.shell('am force-stop MY_PACKAGE_NAME');
const url = encodeURIComponent("MY_H5_URL");
const deeplink = `myapp://browser/?url=${url}`;
await device.shell(`am start -a android.intent.action.VIEW -d "${deeplink}"`);
const webview = await device.webView({
  pkg: "MY_PACKAGE_NAME:web",
});
const page = await webview.page();
const packagePid = await device.shell(`pidof MY_PACKAGE_NAME`).then(buffer => buffer.toString().trim());
setInterval(async () => {
  await device.shell(`top -b -n 1 -d 0.1 -o PID,%CPU,RES -p ${packagePid}`)
  // ...Omit the collecting logic for simplicity
}, 1000);
// deliberately run some CPU intensive task in Webview
await page.evaluate(() => {
  const startTime = Date.now();
  while (Date.now() - startTime < 20_000) { // endless loop for 20 seconds
      Math.sqrt(Math.random());
  }
});

// Calculate the CPU stats from the top outputs collected
// ...Omit the calculation for simplicity
await device.close();