Google: Chrome on Windows has become a lot faster recently

Google rolled out a new feature called Native Window Occlusion, to all Chrome installations on Windows back in October 2020 with the release of Chrome 86. The company has published information on the performance benefits of the feature now in a new blog post on the Chromium website.

Native Window Occlusion expands a Chrome feature that throttles the priority of background tabs to reduce the resource usage of the browser and leave "more memory, CPU and GPU for foreground tabs".

Google engineers noticed that some Chrome windows were covered completely by other windows but their priority was not lowered. Google's Native Window Occlusion feature does that to improve the browser's performance. Google notes that "nearly 20% of Chrome windows are completely covered by other windows".

Through experiments, we found that nearly 20% of Chrome windows are completely covered by other windows, i.e., occluded. If these occluded windows were treated like background tabs, our hypothesis was that we would see significant performance benefits. So, around three years ago, we started working on a project to track the occlusion state of each Chrome window in real time, and lower the priority of tabs in occluded windows. We called this project Native Window Occlusion, because we had to know about the location of native, non-Chrome windows on the user’s screen.

Chrome is monitoring the occlusion state of each of the browser's windows in real-time according to lower the priority of open tabs in windows that are occluded completely on Windows.

Performance has improved significantly in core areas according to Google as a result of enabling the occlusion checking feature on Windows.

8.5% to 25.8% faster startup
3.1% reduction in GPU memory usage
20.4% fewer renderer frames drawn overall
4.5% fewer clients experiencing renderer crashes
3.0% improvement in first input delay
6.7% improvement in first contentful paint and largest contentful paint

The faster startup performance is a result of Chrome skipping work for the occluded window to save resources, which may benefit the foreground window.

Google also found out that the feature reduced crashes by 4.5%.

All of the benefits require that Chrome users have at least two Chrome browser windows open on their devices, and that one of these windows is occluded completely on the desktop.

Native Window Occlusion is only available in Chrome for Windows. Google does not reveal if it will bring the feature to Chrome for Mac OS and Linux in the future.

Closing Words

The 20% figure of occluded Chrome windows seems quite high, even though it only takes into account scenarios in which Chrome users have launched at least two Chrome windows on the Windows system.

Google: Chrome on Windows has become a lot faster recently