grafana/k6 · error

throttling CPU: %w

Error message

throttling CPU: %w

What it means

page.throttleCPU({ rate }) applies a CPUProfile by sending Emulation.setCPUThrottlingRate to the frame's target. This error means the CDP command failed; most commonly because the session/target is invalid at call time, or the browser rejected the rate value.

Source

Thrown at internal/js/modules/k6/browser/common/frame_session.go:1209

	if !initial || offline {
		if err := fs.networkManager.SetOfflineMode(offline); err != nil {
			return fmt.Errorf("updating offline mode for frame %v: %w", fs.targetID, err)
		}
	}

	return nil
}

func (fs *FrameSession) throttleNetwork(networkProfile NetworkProfile) error {
	fs.logger.Debugf("NewFrameSession:throttleNetwork", "sid:%v tid:%v", fs.session.ID(), fs.targetID)

	return fs.networkManager.ThrottleNetwork(networkProfile)
}

func (fs *FrameSession) throttleCPU(cpuProfile CPUProfile) error {
	action := emulation.SetCPUThrottlingRate(cpuProfile.Rate)
	if err := action.Do(cdp.WithExecutor(fs.ctx, fs.session)); err != nil {
		return fmt.Errorf("throttling CPU: %w", err)
	}

	return nil
}

func (fs *FrameSession) updateRequestInterception(enable bool) error {
	fs.logger.Debugf("NewFrameSession:updateRequestInterception",
		"sid:%v tid:%v on:%v",
		fs.session.ID(),
		fs.targetID, enable)

	return fs.networkManager.setRequestInterception(enable)
}

func (fs *FrameSession) updateViewport() error {
	fs.logger.Debugf("NewFrameSession:updateViewport", "sid:%v tid:%v", fs.session.ID(), fs.targetID)

	// other frames don't have viewports and,

View on GitHub (pinned to 93accf6570)

Solutions

1. Use a positive throttling rate (e.g. { rate: 4 } for a 4x slowdown)
2. Apply CPU throttling right after page creation, before navigation, while the target is guaranteed alive
3. Retry once after confirming the page is still open
4. Check for broader CDP failures in the log that indicate a crashed or disconnected browser

Example fix

// before
await page.goto('https://app.example.com');
await page.throttleCPU({ rate: 4 }); // applied mid-lifecycle

// after
await page.throttleCPU({ rate: 4 });
await page.goto('https://app.example.com');

const rate = 4;
if (!(rate > 0)) throw new Error('cpu rate must be positive');
if (!page.isClosed()) { await page.throttleCPU({ rate }); }

When it happens

Trigger: Calling page.throttleCPU (mapped in page_mapping.go) with a rate when the page is closing/closed or the DevTools session dropped; or passing a rate the browser will not accept (zero or negative multiplier).

Common situations: Performance tests throttling CPU to emulate low-end devices; applying throttling late in the iteration; headed browsers in CI crashing; version drift after renaming/moving throttling APIs.

Related errors

• WebSocket endpoint cannot be empty
• can't fetch the page for unknown reason
• errorText
• parent frame has been detached
• adding k6 object to new browser context: %w

AI-assisted analysis of grafana/k6@93accf6570 (2026-08-15). Data as JSON: /api/errors/ce22377067330a7c. Report an issue: GitHub.