The V8 JavaScript engine is a cornerstone of fast browsing in Chrome. Over the course of the past year, the V8 team has developed a new method for measuring performance against snapshots of real web pages. Using insights from real-world measurements, the V8 team improved the speed of the average page load in Chrome by 10-20% over the course of the past year.

Historically, JavaScript engines such as V8 used benchmarks like Octane to improve the “peak” performance of JavaScript, or the performance of CPU-intensive script in hot loops. At the beginning of last year, the V8 team started to measure performance with higher fidelity by instrumenting snapshots of popular web pages such as Reddit, Twitter, Facebook, and Wikipedia. This analysis revealed that while peak performance benefits certain types of large web applications, browsing typical websites relies more on “startup” performance, or the speed it takes to start running script. Using insights gleaned from this real-world performance data, the V8 team implemented optimizations which improved mean page load between Chrome 49 and Chrome 56 by 10-20%, depending on CPU architecture.

The web page snapshots also enabled analysis of the differences between various benchmarks and real web workloads. Although no benchmark can be a representative proxy for all sites, the Speedometer benchmark is an approximation of many sites due to its inclusion of real web frameworks including React, Angular, Ember, and jQuery. This similarity can be seen in the startup optimizations above, which also yielded a 25-35% improvement in Chrome’s Speedometer score. Conversely, comparing page snapshots to Octane revealed that Octane was a poor approximation of most websites. Given the plateau of Octane scores across web browsers and the over-optimization of peak performance, we decided to retire the benchmark as a general-purpose measure of real-world JavaScript performance.

V8 performance optimizations improved Chrome's Speedometer score by 25-35% over the past year

Going forward, we plan to ship more JavaScript performance improvements for new patterns of script appearing on the web, including modern libraries, frameworks, and ES2015+ language features. By measuring real-world websites rather than traditional benchmarks, we can better optimize JavaScript patterns that matter most to users and developers. Stay tuned for updates about our new engine architecture, designed for real-world performance.

Posted by Seth Thompson, V8 Track Commentator