CNS Core: Small: Budgets, Budgets Everywhere: A Necessity for Safe Real-Time on Multicore

多核计算机越来越多地被用于实现实时系统。在实时系统中，存在受时间限制的程序。汽车就是一个很好的例子：当汽车的刹车踏板被踩下时，刹车系统必须在一定的最后期限前做出反应。许多实时系统是安全关键型的，这意味着故障可能会造成灾难性的后果，如生命损失或严重的财务影响。汽车也是安全关键型系统的一个很好的例子；虽然典型的司机可能没有意识到这一点，但现代汽车包含许多运行无数程序的计算机，这些程序执行转向、刹车、发动机控制等所需的功能。安全关键型实时系统通常必须经过认证过程，以确保重要功能得到适当支持。此过程的一个重要部分是验证是否满足截止日期要求，即程序是否“按时”执行。要做到这一点，应该知道程序的最坏情况执行时间(WCET)。不幸的是，在当今复杂的多核计算机上，很难确定准确的WCET，因为程序的最坏情况执行时间可能在极少数情况下发生，因此很难重现。对于完全不了解WCET的传统防御措施是让操作系统(OS)强制执行预算；程序的预算是操作系统确保不会超过其执行时间的限制。虽然预算通常是在程序级别强制执行，但在当今挑战感兴趣的实时应用程序时，需要在许多级别执行这种强制执行。例如，在自动驾驶汽车中，整个系统被分成几个子系统，每个子系统提供一些单独的功能，例如，感知道路上的障碍物，计算对障碍物的反应计划等。这些子系统，每个可能包含许多程序，也应该受到预算执行的影响。例如，如果障碍物感知子系统花费了太多时间，那么执行规划子系统就没有意义。该项目的目标是(I)确定在复杂的多核实时应用程序中必须执行预算的各个级别，(Ii)检查将多级预算执行作为首要问题对实时安全认证产生的影响，以及(Iii)有效地实施这种执行。解决这些目标将使开发出更安全的系统。在更广泛的影响方面，将特别重视对女孩和妇女的宣传。这样的推广活动将包括：北卡罗来纳大学计算机科学专业毕业生女性(GWiCS)小组的活动，该组织每年举办一次针对本科生女性和其他代表性不足的少数族裔的研究研讨会；针对当地初中和高中女孩的黑客马拉松Tar Heel Hack；北卡罗来纳大学计算机科学的Girls Who Code Club，为当地6-12年级的女孩提供一个学习计算机科学的社区；以及北卡罗来纳大学计算机科学年度开放参观和科学博览会。将在PI领导的名为Themes(Talking Over Papers In Computer Science)的本科生女性计算机科学俱乐部的背景下，进一步扩大对女性学生的支持。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Multicore computers are increasingly being used to implement real-time systems. In a real-time system, programs exist that are subject to timing constraints. An automobile is a good example: When a car's brake pedal is depressed, the braking system must react by a certain deadline. Many real-time systems are safety-critical, meaning that failures may have catastrophic consequences, such as loss of life or serious financial repercussions. Automobiles are also a good example of a safety-critical system; while a typical driver may be unaware of it, modern cars contain many computers that run a myriad of programs that perform functions required for steering, braking, engine control, etc. Safety-critical real-time systems typically must undergo a certification process that ensures that important functionality is properly supported. An important part of this process is to validate that deadline requirements are met, i.e., that programs execute "on time." To do this, worst-case execution times (WCETs) of programs should be known. Unfortunately, on today's complex multicore computers, determining accurate WCETs is difficult because the worst-case execution time of a program may occur under rare circumstances and thus be difficult to reproduce. The traditional defense against not knowing WCETs with absolute certainty is to have the operating system (OS) enforce execution budgets; a program's budget is a limit on its execution time that the OS ensures won't be exceeded.While budgets have conventionally been enforced at the program level, in challenging real-time applications of interest today, such enforcement is needed at many levels. For example, in an autonomous vehicle, the overall system is broken into subsystems, where each subsystem provides some separate function, e.g., sensing obstacles in the road, computing a plan to react to obstacles, etc. These subsystems, which may contain many programs each, should be subject to budget enforcement as well. For instance, if the obstacle-sensing subsystem takes too much time, then executing the planning subsystem is pointless. This project is directed at (i) identifying the various levels at which budgets must be enforced in complex multicore real-time applications, (ii) examining the implications for real-time safety certification that arise from making multi-level budget enforcement a first-class concern, and (iii) producing efficient implementations of such enforcement. Addressing these goals will enable safer systems to be developed. In terms of broader impacts, a special emphasis will be placed on outreach to girls and women. Such outreach will include: events involving the Graduate Women in Computer Science (GWiCS) group at UNC, which hosts an annual research symposium targeted toward undergraduate women and other underrepresented minorities; Tar Heel Hack, a hackathon for local middle and high school girls; UNC Computer Science's Girls Who Code Club, which provides local girls in grades 6-12 with a community for learning about computer science; and UNC Computer Science's annual Open House and Science Expo. Further outreach to female students will be done in the context of a computer science club for undergraduate women led by the PI called TOPICS (Talking Over Papers In Computer Science).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.