Unpacking Cloudflare Workers CPU Performance Benchmarks

Summary

On October 4, independent developer Theo Browne published a series of benchmarks designed to compare server-side JavaScript execution speed between Cloudflare Workers and Vercel, a competing compute platform built on AWS Lambda. The initial results showed Cloudflare Workers performing worse than Node.js on Vercel at a variety of CPU-intensive tasks, by a factor of as much as 3.5x.We were surprised by the results. The benchmarks were designed to compare JavaScript execution speed in a CPU-intensive workload that never waits on external services. But, Cloudflare Workers and Node.js both use the same underlying JavaScript engine: V8, the open source engine from Google Chrome. Hence, one would expect the benchmarks to be executing essentially identical code in each environment. Physical CPUs can vary in performance, but modern server CPUs do not vary by anywhere near 3.5x.On investigation, we discovered a wide range of small problems that contributed to the disparity, ranging from some bad tuning in our infrastructure, to differences between the JavaScript libraries used on each platform, to some issues with the test itself. We spent the week working on many of these problems, which means over the past week Workers got better and faster for all of our customers. We even fixed some problems that affect other compute providers but not us, such as an issue that made trigonometry functions much slower on Vercel. This post will dig into all the gory details. It's important to note that the original benchmark was not representative of billable CPU usage on Cloudflare, nor did the issues involved impact most typical workloads. Most of the disparity was an artifact of the specific benchmark methodology. Read on to understand why.With our fixes, the results now look much more like we'd expect: There is still work to do, but we're happy to say that after these changes, Cloudflare now performs on par with Vercel in every benchmark case except the one based on Next.js. On that benc...