CSR: Small: Running the Kernel Continuously with Simultaneous Multi-Threading

CSR：小：通过同时多线程连续运行内核

• 批准号: 1617992
• 负责人: Jakob Eriksson
• 金额: $ 50万
• 依托单位: University of Illinois at Chicago
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-10-01 至 2020-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1617992&HistoricalAwards=false
• 关键词: CSR; Small; Running; Kernel; Continuously; CSR; Small; Running; Kernel; Continuously

Since 2002, many commodity computer processors include a feature called simultaneous multi-threading (SMT), marketed by Intel as Hyperthreading (tm). SMT enables a single processor core to perform two or more tasks in parallel. Until now, operating systems researchers have focused on accommodating SMT in existing operating system designs, investigating topics such as SMT-aware resource allocation, scheduling and synchronization methods. In this project, rather than merely accommodate SMT, we investigate a new low-level operating system design that is enabled by SMT hardware. In modern operating systems, the processor switches between the safe but quite limited 'user mode' which is used to run applications, and the unsafe but all-powerful 'supervisor mode' which is available only to the operating system. Sometimes, these switches occur millions of times per second, providing an illusion of parallel operation. In our new design, the user and supervisor modes are actually active simultaneously, but on separate SMT threads. This avoids the often high cost of frequent mode switches, and enables new efficiency and design improvements throughout the operating system. Based on preliminary measurements, we find that the throughput gains provided by conventional SMT diminishes rapidly with the number of processor cores in a system, as a result of sub-linear scalability in the application. To counter this, and to make better use of existing hardware, we propose the "cokernel" operating system design principle, where one hardware thread per CPU is dedicated to continuously executing the kernel. By offloading kernel duties from the other hardware thread(s), a cokernel operating system enables higher per-thread application throughput, avoiding scalability concerns. In addition, having a continuously executing kernel thread on each core enables a wide range of improvements to other aspects of the kernel, such as replacing most system calls with message passing, hybrid cooperative-preemptive process scheduling, kernel-assisted asynchronous inter-core and inter-socket communication and true kernel background tasks.

自2002年以来，许多商品计算机处理器都包含一个称为同时多线程（SMT）的功能，该功能由英特尔（Intel）销售为HyperThreading（TM）。 SMT使单个处理器核心可以并行执行两个或多个任务。到目前为止，研究人员的重点是在现有操作系统设计中适应SMT，并研究了SMT感知资源分配，调度和同步方法等主题。在这个项目中，我们不仅要容纳SMT，还研究了由SMT硬件启用的新的低级操作系统设计。在现代操作系统中，处理器在用于运行应用程序的安全但相当有限的“用户模式”之间进行切换，以及仅适用于操作系统的不安全但无能的“主管模式”。有时，这些开关每秒发生数百万次，提供了平行操作的幻想。在我们的新设计中，用户和主管模式实际上同时处于活动状态，但是在单独的SMT线程上。这避免了频繁模式开关通常很高的成本，并在整个操作系统中实现了新的效率和设计改进。基于初步测量，我们发现传统SMT提供的吞吐量增长迅速减少了系统中的处理器芯的数量，这是由于应用程序中的次线性可伸缩性而导致的。为了解决这个问题，并更好地利用现有硬件，我们提出了“ cokernel”操作系统设计原理，其中每个CPU的一个硬件线程致力于连续执行内核。通过从其他硬件线程中卸载内核职责，Cokernel操作系统可实现更高的每线应用程序吞吐量，从而避免可扩展性问题。此外，在每个核心上具有连续执行的内核线程，可以对内核的其他方面进行广泛的改进，例如，通过消息传递，混合合作的抢夺过程调度来替换大多数系统调用，内核辅助下的核心间式核心间和套管间交流以及套接字交流和真实的内核背景。