摘要:人工智能技术的长足发展对于云计算的算力提出了更高的要求，云服务提供商在数据中心内添置了拥有大量并行计算单元的加速器，这些加速器需要与已有的虚拟化平台相结合以进行计算资源的划分.当前主流的加速器虚拟化方案是通过PCI透传的方式，但是该方式不支持细粒度的资源划分；部分特定型号的加速器还支持了时分复用的方案，通过硬件与虚拟机监视器配合划分计算资源和时间片，但是该方案可移植性差，对于任何新型加速器的适配都要重新开发，固定的资源划分策略也导致可扩展性有限；另有基于API转发的方案，通过分离式驱动的模式将虚拟机的请求转发给后端驱动处理，而转发通信的过程中存在着性能瓶颈.提出了Wormhole，一种基于C/S架构的、支持跨虚拟机快速代理执行的加速器虚拟化框架，旨在为上层用户提供高效、透明的加速器API转发虚拟化的同时保障多用户间的强隔离性.该框架利用硬件虚拟化技术，允许CPU控制流在虚拟机间快速切换而不触发任何下陷，大幅降低了虚拟机间通信带来的虚拟化性能开销.实验结果表明，Wormhole的原型系统相较于具有代表性的开源虚拟化方案GvirtuS，在经典模型的训练测试中能够有高达5倍的性能提升.



Abstract:The increasing deployment of artificial intelligence has placed unprecedent requirements on the computing power of cloud computing. Cloud service providers have integrated accelerators with massive parallel computing units in the data center. These accelerators need to be combined with existing virtualization platforms to partition the computing resources. The current mainstream accelerator virtualization solution is through the PCI passthrough approach, which however does not support fine-grained resource provisioning. Some manufacturers also start to provide time-sliced multiplexing schemes, and use drivers to cooperate with specific hardware to divide resources and time slices to different virtual machines, which unfortunately suffer from poor portability and flexibility. One alternative another but promising approach is based on API forwarding, which forwards the virtual machine's request to the back-end driver for processing through a separate driver model. Yet, the communication due to API forwarding can easily become the performance bottleneck. This study proposes Wormhole, an accelerator virtualization framework based on the C/S architecture that supports rapid delegated execution across virtual machines. It aims to provide upper-level users with an efficient and transparent way to accelerate accelerator virtualization with API forwarding while ensuring strong isolation between multiple users. By leveraging hardware virtualization feature, the framework minimizes performance degradation through exitless cross-VM control flow switch. Experimental results show that Wormhole’s prototype system can achieve up to 5 times performance improvement over the classic open-source virtualization solution such as GVirtuS in the training test of the classic model.



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