XPS: FULL:CCA: Extracting Scalable Parallelism by Relaxing the Contracts across the System Stack

技术扩展趋势已使并行性成为在从高端计算到嵌入式平台的各种计算环境中增强性能的事实上标准。然而，软件在提取底层硬件平台提供的可用并行性方面的能力严重落后，这主要是因为系统堆栈的不同层之间的划分合同。严格的合同限制了在层内和层之间利用性能/功率/正确性权衡的丰富设计空间的能力，这可以通过稍微偏离合同来实现。尽管这种被称为近似计算的宽松合同最近受到了关注，但这一领域的许多工作仍然是划分的，缺乏一种整体的跨层战略，以最大限度地提高并行性，同时坚持能力和正确性要求。因此，该项目的动机是探索一种全面的跨层方法来近似跨越应用程序、运行时系统、编译器和硬件的计算，从而打破层之间的僵化契约，同时仍然允许它们协作，以在高端和移动计算环境中跨不同的应用程序集提取可实现的并行性。具体地说，它涉及到对计算、数据访问和同步的近似范围的应用级分析，设计能够促进和受益于近似的高效硬件机制，以及开发编译器和运行时支持，以便以体系结构感知的方式表达、利用和评估/验证近似。这种跨层的近似计算方法有望在未来十年及以后实现可伸缩的并行性，并可能对计算行业产生重大影响。此外，从该项目开发的工具和模型在公共领域传播给更广泛的研究社区，私人投资机构参与各种外联活动，例如通过宾夕法尼亚州立大学Eberly学院的Explore-U倡议招募妇女和少数族裔以及让当地高中生参与。

Technology scaling trends have made parallelism the de-facto standard for enhancing performance across a spectrum of computing environments spanning from high-end computing to embedded platforms. Yet, the software is woefully lagging in its ability to extract usable parallelism offered by the underlying hardware platforms primarily because of the compartmentalized contracts between the different layers of the system stack. Rigid contracts restrict the ability to leverage a rich design space of performance/power/correctness trade-offs within and across layers, that could be achievable by straying slightly from the contract. Although such a relaxed contract, referred to as approximate computing, has received attention recently, much of the work in this area is still compartmentalized and lacks a holistic cross-layer strategy to maximize parallelism, while adhering to power and correctness mandates. Thus, the motivation of this project is to explore a holistic cross-layer approach to approximate computing spanning application, runtime system, compiler and hardware, thereby breaking the rigidity of the contracts between the layers, while still allowing them to cooperate for extracting the achievable parallelism across a diverse set of applications in both the high-end and mobile computing environments. Specifically, it involves application-level analysis of the scope of approximation for computation, data access and synchronization, designing efficient hardware mechanisms that could facilitate and benefit from approximation, and developing compiler and runtime support for expressing, exploiting and evaluating/validating the approximations in an architecture-aware fashion. This cross-layer approach to approximate computing is expected to play a crucial role towards achieving scalable parallelism for the next decade and beyond, with a potentially high impact to the computing industry. In addition, the tools and models developed from this project are disseminated in the public domain to a broader research community, and the PIs engage in a variety of outreach activities such as recruiting women and minority and involvement of local high school students through Penn State Eberly College's Exploration-U initiatives.