[2003.06477] Web Performance with Android's Battery-Saver Mode

A Web browser utilizes a device's CPU to parse HTML, build a Document ObjectModel, a Cascading Style Sheets Object Model, and render trees, and parse,compile, and execute computationally-heavy JavaScript. A powerful CPU isrequired to perform these tasks as quickly as possible and provide the userwith a great experience. However, increased CPU performance comes withincreased power consumption and reduced battery life on mobile devices. As anoption to extend battery life, Android offers a battery-saver mode that whenactivated, turns off the power-hungry and faster processor cores and turns onthe battery-conserving and slower processor cores on the device. The transitionfrom using faster processor cores to using slower processor cores throttles theCPU clock speed on the device, and therefore impacts the webpage load process.We utilize a large-scale data-set collected by a real user monitoring system ofa major content delivery network to investigate the impact of Android'sbattery-saver mode on various mobile Web performance metrics. Our analysissuggests that users of select smartphones of Huawei and Sony experience asudden or gradual degradation in Web performance when battery-saver mode isactive. Battery-saver mode on newer flagship smartphones, however, does notimpact the mobile Web performance. Finally, we encourage for new website designgoals that treat slow (and throttled-CPU) devices kindly in favor of improvingend-user experience and suggest that Web performance measurements should beaware of user device battery charge levels to correctly associate Webperformance.