Latency awareness in operating systems for massively parallel processors

LAOS研究了同步并发共享内存进程中延迟的对策。因此，第一阶段在系统软件开发时形成预防措施，即建设性措施，以避免在运行时演变的过程延迟。在仅靠预防措施不起作用的情况下，第二步的目标是至少避免在这些潜伏期内出现强烈的抖动。如果即使是那些避免进程延迟的减少措施也不有效，则第三阶段的尝试是在适用的情况下隐藏延迟。持续量化或分别监控处理延迟并试图通过调度手段将其降低到最低程度的分析措施不是该项目的主题。该项目继续的重点是隐藏在所谓的守卫部分的延迟。与临界区的常规实现不同，受保护的区不受并发共享内存进程的互斥。相反，争用的进程为控制通过临界区的进程留下连续的、可工作的任务。分配按照无等待的同步排队原则进行排队和服务。遇到非活动的受保护部分的授权进程会激活它，并接管队列处理中的领导权。争用的进程总是非阻塞和无等待地通过受保护的部分。但是，如果需要，它们会因为事件的条件同步而阻塞，该事件指示将不同于节的计算值分配给某个占位符变量。为了支持受保护的程序段，开发了一个无等待的同步操作系统内核，为优先级控制进程的条件同步提供所需的最小系统功能基础。该项目源于对非顺序程序特别是操作系统程序中关键段的保护的现有知识。它的基本假设是，通过由保护段支持的临界区的异步顺序执行，一方面增加了并行进程的程度，另一方面加强了多核处理器在时间和空间上的缓存局部性，从而提高了非顺序程序的性能。进程调度策略和受保护部分的进入/退出协议之间的特定相互关系受到了挑战。关于现有系统和遗留系统在适用性、可转移性和对已开发的概念和技术的概括方面的一般关系也受到质疑。

LAOS investigates countermeasures to latencies in the synchronisation of concurrent shared-memory processes. The first stage thereby forms prevention, namlely constructive measures at system-software development time that avert process latencies to evolve at run-time. Where prophylaxis alone cannot help, objective of a second step is to avoid at least strong jitter in those latencies. If even those abatement measures of process-latency avoidance are not effective, attempt of the third stage is to hide latency wherever applicable. Analytical measures that continuously quantify or monitor, respectively, process latencies and try to level and minimise them by means of scheduling are no subject of the project.Emphasis of the project continuation is latency hiding through so called guarded sections. In contrast to the conventional implementation of critical sections, guarded sections are not subject to mutual exclusion of concurrent shared-memory processes. Instead, contending processes leave sequential workably mandates for a process that controls passage through the critical section. The assignments are queued and served following a wait-free synchronised queuing discipline. A mandating process that encounters an inactive guarded section activates it and takes over leadership in queue processing. Contending processes always pass a guarded section non-blocking and wait-free. As needed, they however block due to conditional synchronisation on the event indicating the assignment of a section-distinct computational value to some placeholder variable. In order to support guarded sections, a wait-free synchronised operating-system kernel is developed to provide the required minimal basis of system functions for conditional synchronisation for priority-controlled processes.The project emanates from existing knowledge of protecting critical sections in non-sequential programs in general and operating-system programs in particular. It makes the basic assumption that, through asynchronous sequential execution of critical sections supported by guarded sections, performance of non-sequential programs improves because of increased degree of parallel processes, on the one hand, and strenghtening cache locality of many-core processors in time and space, on the other hand. The specific interrelation between process-scheduling strategies and entry/exit protocols of guarded sections is challenged. Also questioned is the general relationship as to current and legacy systems in terms of applicability, transferability, and generalisation of the developed concepts and techniques.