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

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，许多商用计算机处理器都包含一项称为同步多线程 (SMT) 的功能，英特尔将其称为超线程 (tm)。 SMT 使单个处理器核心能够并行执行两个或多个任务。到目前为止，操作系统研究人员一直专注于在现有操作系统设计中容纳 SMT，研究诸如 SMT 感知的资源分配、调度和同步方法等主题。在这个项目中，我们不仅研究了 SMT，还研究了一种由 SMT 硬件支持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”和仅适用于操作系统的不安全但功能强大的“管理程序模式”之间切换。有时，这些切换每秒发生数百万次，给人一种并行操作的错觉。在我们的新设计中，用户和管理员模式实际上是同时活动的，但在单独的 SMT 线程上。这避免了频繁模式切换的高成本，并在整个操作系统中实现新的效率和设计改进。根据初步测量，我们发现，由于应用程序中的次线性可扩展性，传统 SMT 提供的吞吐量增益随着系统中处理器内核数量的增加而迅速减少。为了解决这个问题，并更好地利用现有硬件，我们提出了“cokernel”操作系统设计原则，其中每个 CPU 一个硬件线程专用于连续执行内核。通过从其他硬件线程卸载内核职责，共内核操作系统可以实现更高的每线程应用程序吞吐量，从而避免可扩展性问题。此外，每个内核上都有一个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，例如用消息传递替换大多数系统调用、混合协作抢占式进程调度、内核辅助的异步内核间和套接字间通信和真正的内核后台任务。