AI 中文总结
针对异构分层作用域一致性协议衔接层手动设计易出错的问题，提出ShimGen自动合成引擎，结合SWMR与非SWMR访问协议，实验验证其一致性与性能优势。
AI 中文摘要
处理器设计正逐步采用以异构性、分层结构和作用域为特征的新型缓存一致性共享内存模型。CXL或AMBA CHI等协议被用作全局协议，以组合多个集群，每个集群有其自身的集群级一致性协议。手动设计用于连接这些集群协议与全局协议的衔接层（shim）是一项微妙且易出错的工作。另一方面，自动合成会做出诸如单写多读（SWMR）不变式之类的简化假设，为了简洁性和保证正确性而牺牲性能。我们提出了一种衔接层API——一种通用抽象，使我们能够根据协议事务的语义一致性保证对其进行分类。我们的自动合成引擎ShimGen利用该衔接层API自动组合包含SWMR访问和宽松访问的协议，同时利用作用域内存访问、延迟失效等现代架构优化。我们在两个案例研究中验证了ShimGen的有效性：首先，将其输出与gem5中发布的AMD APU的手动设计分层协议进行比较，ShimGen的输出与现有协议相近，但我们发现手动设计协议存在无法维持复合一致性的场景，而ShimGen的输出可维持；其次，将利用非SWMR访问的分层协议与严格SWMR全局协议的分层协议进行性能比较，结果显示，适配具有非SWMR行为的全局协议可带来性能提升。
英文摘要
Processor design is converging on a new model of cache-coherent shared memory characterized by heterogeneity, hierarchy, and scopes. Protocols like CXL or AMBA CHI are used as global protocols to combine multiple clusters, each with its own cluster-level coherence protocols. Manually designing shims to interface between these cluster and global protocols is subtle and error-prone. Automatic synthesis, on the other hand, makes simplifying assumptions like the single-writer multiple-reader (SWMR) invariant, that sacrifice performance for simplicity and guaranteed correctness. We present a shim API \textemdash a generic abstraction that enables us to classify protocol transactions by their semantic coherence guarantees. Our automated synthesis engine, ShimGen, uses this shim API to automatically compose protocols with both SWMR and relaxed accesses, taking advantage of modern architectural optimizations like scoped memory accesses and lazy invalidation. We demonstrate ShimGen's efficacy on two case studies. First, we compare its output to a manually-designed hierarchical protocol for the AMD APU released in gem5. ShimGen's output is similar to the existing protocol. However, we identify one scenario where the manually-designed protocol fails to uphold compound consistency, while ShimGen's does. Second, we compare the performance of a hierarchical protocol with a global protocol that exploits non-SWMR accesses to a hierarchical protocol with a strictly SWMR global protocol. The result shows the performance benefits of accommodating global protocols with non-SWMR behavior.
