Understanding the performance of webassembly applications

Yutian Yan, Tengfei Tu, Lijian Zhao, Yuchen Zhou, Weihang Wang

Abstract: WebAssembly is the newest language to arrive on the web. It features a compact binary format, making it fast to be loaded and decoded. While WebAssembly is generally expected to be faster than JavaScript, there have been mixed results in proving which code is faster. Little research has been done to comprehend WebAssembly's performance benefit. In this paper, we conduct a systematic study to understand the performance of WebAssembly applications and compare it with JavaScript. Our measurements were performed on three sets of subject programs with diverse settings. Among others, our findings include: (1) WebAssembly compilers are commonly built atop LLVM, where their optimizations are not tailored for WebAssembly. We show that these optimizations often become ineffective for WebAssembly, leading to counter-intuitive results. (2) JIT optimization has a significant impact on JavaScript performance. However, no substantial performance increase was observed for WebAssembly with JIT. (3) The performance of WebAssembly and JavaScript varies substantially depending on the execution environment. (4) WebAssembly uses significantly more memory than its JavaScript counterparts. We hope that our findings can help WebAssembly tooling developers identify optimization opportunities. We also report the challenges encountered when compiling C benchmarks to WebAssembly and discuss our solutions.