Public cloud serverless platforms have attracted a large user base due to their high scalability, plug-and-play deployment model, and pay-per-use billing. However, compared to virtual machines and container hosting services, modern serverless offerings typically impose higher per-unit time and resource charges. Additionally, billing practices such as wall-clock time allocation-based billing, invocation fees, and usage rounding up can further increase costs. This work, for the first time, holistically demystifies these costs by conducting an in-depth, top-down characterization and analysis from user-facing billing models, through request serving architectures, and down to operating system scheduling on major public serverless platforms. We quantify, for the first time, how current billing practices inflate billable resources up to 4.35x beyond actual consumption. Also, our analysis reveals previously unreported cost drivers, such as operational patterns of serving architectures that create overheads, details of resource allocation during keep-alive periods, and OS scheduling granularity effects that directly impact both performance and billing. By tracing the sources of costs from billing models down to OS scheduling, we uncover the rationale behind today's expensive serverless billing model and practices and provide insights for designing performant and cost-effective serverless systems.

翻译：公有云无服务器平台凭借其高可扩展性、即插即用部署模式及按使用量计费的特点，吸引了大量用户。然而，相较于虚拟机与容器托管服务，现代无服务器产品通常收取更高的单位时间与资源费用。此外，基于挂钟时间分配的计费方式、调用费用及使用量向上取整等计费实践可能进一步推高成本。本研究首次通过自上而下的深度特征分析与剖析，从面向用户的计费模型、请求服务架构直至主流公有无服务器平台的操作系统调度层面，全面揭示了这些成本构成。我们首次量化了当前计费实践如何将可计费资源膨胀至实际消耗量的4.35倍。同时，我们的分析揭示了先前未被报告的成本驱动因素，例如：产生开销的服务架构运行模式、保活期间资源分配的具体细节，以及直接影响性能与计费的操作系统调度粒度效应。通过从计费模型到操作系统调度的成本溯源，我们揭示了当前昂贵无服务器计费模型与实践背后的逻辑依据，并为设计高性能、高成本效益的无服务器系统提供了见解。