CSR-PDOS: Out-of-Context Prefetching for L2 Caches

CSR-PDOS：L2 缓存的上下文外预取

• 批准号: 0720741
• 负责人: Sohum Sohoni
• 金额: --
• 依托单位: Oklahoma State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-08-01 至 2010-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0720741&HistoricalAwards=false
• 关键词: CSR; PDOS; Out; Context; Prefetching

On a multi-tasked system, the CPU cycles through a number of processes every few milliseconds. Some of the processes are memory-intensive, but most are non-intensive support processes and other user programs such as text-editors, email clients, and instant messengers. A typical system cycles through a few memory-intensive processes, each of which replaces several cache blocks from the level-2 cache from other processes. This results in a large number of demand misses for the L2, and ties up the memory subsystem preventing effective prefetching.This project investigates a possible solution to this problem by modifying the OS to prefetch to the L2 out of context, i.e. when the CPU is executing a non memory-intensive process. (ideally, just before the memory-intensive process will be brought in for execution). Thus, when this process resumes execution, it will have low L2 cache misses which in turn will keep the memory-bus free in order to prefetch even more blocks. Out-of-context prefetching aims to shift from a predominantly demand-fetched paradigm to a predominantly prefetched paradigm.In conjunction with accurate predictors for prefetching, this work has the potential to greatly mitigate the performance CPU-memory gap problem on a system-wide level. The expected outcome of the project is a Linux implementation of out-of-context prefetching on a full-system simulator, and a website that documents all the assumptions, the source code, and extensive project results beyond those published in the corresponding research literature. All researchers, operating system designers, and processor manufacturers will have access to the website and the research findings to freely incorporate them as they wish.

在多任务系统上，CPU 每隔几毫秒循环执行多个进程。其中一些进程是内存密集型的，但大多数是非密集型支持进程和其他用户程序，例如文本编辑器、电子邮件客户端和即时通讯程序。典型的系统会循环执行几个内存密集型进程，每个进程都会从其他进程中替换二级缓存中的多个缓存块。这会导致 L2 出现大量需求缺失，并占用内存子系统，从而阻止有效的预取。该项目通过修改操作系统以在上下文之外预取 L2（即当 CPU 正在执行非内存密集型进程时）来研究此问题的可能解决方案。 （理想情况下，就在内存密集型进程被引入执行之前）。因此，当该进程恢复执行时，L2 缓存未命中率较低，这反过来又会保持内存总线空闲，以便预取更多块。脱离上下文预取的目的是从占主导地位的按需获取范式转变为占主导地位的预取范式。与预取的准确预测器相结合，这项工作有可能在系统范围内极大地缓解性能 CPU-内存差距问题。该项目的预期成果是在全系统模拟器上实现脱离上下文预取的 Linux 实现，以及一个记录所有假设、源代码和超出相应研究文献中发布的广泛项目结果的网站。所有研究人员、操作系统设计者和处理器制造商都可以访问该网站和研究结果，并根据自己的意愿自由地合并它们。