High CPU Spike / UI Stutter on Single GM_xmlhttpRequest Call

[neilmahaseth]

Calling GM_xmlhttpRequest even at a low frequency (once every 10 seconds) causes a noticeable CPU spike (~50%) in Chrome’s internal task manager and results in visible UI stutter/freezing for a short duration.
This behavior occurs even with a minimal request and no heavy processing in the callback.

Actual Behavior

• CPU spike (~40–50%) in Chrome Task Manager when Calling GM_xmlhttpRequest
• Short UI stutter/freezing during execution
• Issue occurs even without response processing or DOM manipulation

Expected Behavior

• Minimal CPU usage for a simple HTTP GET request
• No visible UI stutter or freezing
• Behavior similar to native fetch()

Steps to reproduce the issue

1. Install Tampermonkey
2. Add the bellow mentioded minimal userscript
3. Open www.google.com
4. Open Chrome Task Manager (Shift + Esc)
5. Observe CPU usage and UI behavior when request fires

Environment

• Browser and Version: Chrome 146.0.7680.154 (Official Build) (64-bit)
• Tampermonkey version:5.4.1
• Operating System and Version: Windows 10 10.0.19045 Build 19045

Script

// ==UserScript==
// @name         New Userscript
// @namespace    http://tampermonkey.net/
// @version      2026-03-22
// @description  try to take over the world!
// @author       You
// @match        https://www.google.com/
// @icon         https://www.google.com/s2/favicons?sz=64&domain=google.com
// @grant        GM_xmlhttpRequest
// @connect      httpbin.org
// ==/UserScript==

(function() {
    'use strict';
setInterval(() => {
  GM_xmlhttpRequest({
    method: "GET",
    url: "https://httpbin.org/get",
    onload: () => console.log("done"),
    onerror: (err) => console.error("error", err),
  });
}, 10000); // 10 seconds
    // Your code here...
})();

Additional context

• The spike is not visible in Windows Task Manager, indicating short-lived internal thread blocking rather than sustained CPU usage
• Issue persists even at low frequency (10s interval)

[saumil94]

Did you find a solution? I also have the same stutters and it's annoying as it affects all tabs

[saumil94]

@derjanb here's what claude suggests, I'm merely pasting if it helps us all:

Same issue from a different angle — GM_xmlhttpRequest causes 40-50% CPU spikes in Chrome Task Manager even at 1 request per 10 seconds. The key insight: "not visible in Windows Task Manager, indicating short-lived internal thread blocking" — it's Chrome-internal IPC overhead, not actual CPU work.

From TM's perspective, here's what I think the fix paths are:

Why it's slow: In MV3, Tampermonkey runs GM_xmlhttpRequest through the service worker. The flow is:

Content script (our code)
→ chrome.runtime.sendMessage to service worker (IPC)
→ service worker wakes up (if suspended)
→ fetch() in service worker context
→ chrome.runtime.sendMessage back (IPC)
→ callback in content script
Each IPC hop involves serializing/deserializing the entire request+response, and the service worker may be suspended between calls (MV3 aggressively suspends them). The wake-up + serialize + deserialize cycle is what causes the freeze.

Possible fixes from TM's side:

Use chrome.offscreen API — MV3 allows creating an offscreen document that can run fetch() without the service worker hop. Persistent, no wake-up penalty.

Batch IPC — instead of one sendMessage per GM_xmlhttpRequest, batch multiple pending requests into a single IPC round-trip.

Use declarativeNetRequest for simple GET requests — avoids the IPC entirely for read-only requests, though this only works for specific patterns.

Keep service worker alive — TM could use the chrome.alarms API or periodic keepalive to prevent the service worker from suspending between calls, eliminating the wake-up cost.