Leveraging Processor-diversity For Improved Performance In Heterogeneous-ISA Systems

dc.contributor.authorPang, Yihanen
dc.contributor.committeechairRavindran, Binoyen
dc.contributor.committeememberMin, Chang Wooen
dc.contributor.committeememberPatterson, Cameron D.en
dc.contributor.departmentElectrical and Computer Engineeringen
dc.description.abstractThe purpose of this thesis is to investigate the effectiveness of executing High Performance Computing (HPC) workloads on multiprocessors with heterogeneous Instruction Set Architecture (ISA) cores. ISA-heterogeneity in processor designs provides a unique dimension for researchers to explore performance benefits through diversity in design choices. Additionally, each application has a natural preference to one processor in a selected group of processors (we defined this term as processor-preference), and processor-preference is highly affected by processor design choices. Thus, a system with heterogeneous-ISA cores offers an intriguing design perspective, packing heterogeneous-ISA cores in the same processor or system that compensate each other in dynamic workload scenarios. This thesis considers dynamic migrating applications with different processor-preferences across ISA-different cores to exploit the potential of this idea. With SIMD instructions getting more attention from chip designers, this thesis also presents the necessary modifications for a general compiler/run-time infrastructure to transform the dynamic program state of SIMD regions at run-time from one ISA format to another for cross-ISA migration and execution. Lastly, this thesis presents a processor-preference-aware scheduling policy that makes dynamic cross-ISA migration decisions that improve overall system throughput compared to homogeneous-ISA systems. This thesis prototypes a heterogeneous-ISA system using an Intel Xeon Gold 5118 x86-64 server and a Cavium ThunderX ARMv8 server and evaluates the effectiveness of our infrastructure and scheduling policy. Our results reveal that heterogeneous-ISA systems that are processor-preference-aware and with cross-ISA execution migration capability can yield throughput gains up to 36\% compared to traditional homogeneous ISA systems.en
dc.description.abstractgeneralThe author of this thesis has a family full of non-engineers. To persuade family members that the work of this thesis is meaningful, aka the author is not procrastinating in school, the author decided to draw an analogy between processors and cars. Suppose in an alternative universe, cars (systems) can be powered by engines (processors) that uses two different fuel-sources (ISAs): gasoline or electric (single-ISA) processors but not both (heterogeneous-ISA). Car manufacturers (chip designers) can build engines with different design choices (processors with varying design options): engines combined with turbochargers for gasoline-powered cars, high-performance batteries combined with energy-efficient batteries for electric-powered cars (added extended instruction sets, CPU designs that target vastly different use cases, etc.). However, each design choice is limited to improving performance for a specific type of fuel-source based engine. For example, having battery alternatives has no performance impact on gasoline-powered engines. As time passes by, car manufacturers have exhausted options to make a drastic improvement to their existing engine designs (limited performance gains in recent chips). To tackle this problem, in this thesis, the author first examined the usage of cars: driving on the road (running applications). The author's study found that no single engine is suitable for all routes (no single processor is good for all workloads), and cars powered by different fuel-source based engines showed a significant diversity in performance (application performance varies drastically between systems with processors built on different ISAs). Gasoline-powered cars perform well on high-speed roads, whereas electric-powered cars perform well on low-speed roads. Unfortunately, in real life, a person's commute (a workload of applications) consists of a mixture of high-speed roads and low-speed roads, and one cannot know the exact percentage of each kind of path they travel (exact application composition in a workload) beforehand. Therefore it is challenging for a person to make the correct car selection for the incoming commute (choose the right system for a workload). This thesis tries to solve this commuting problem by building a car that has multiple engines fitted to suit different road needs (systems with processors that have vastly different use cases). This thesis looks at a particular dimension of combining various fuel-powered engines in the same car (a system with heterogeneous-ISA processors). The author believes that adding diversity in fuel-powered engine selections provide an exciting dimension in car design choices (adding ISA-heterogeneity in processors provide a unique dimension in system design). Thus, this thesis focuses on estimating a theoretical multi fuel-powered car's performance by combining two different fuel-powered cars into a single mega-car using some framework (Popcorn Linux). This framework allows this mega-car to be driven by a combined fuel source with fuel intake freely transfer between fuel-sources (cross-ISA migration and execution) based on road conditions (application encountered). Based on the evaluation of this new prototype, the author finds that in a real-life scenario (workload with mixed application combination), cars with multiple fuel-source based engines have better performance than two single fuel-source based cars (systems with heterogeneous-ISAs processors perform better than systems with homogeneous-ISAs processors). The author hopes that this study can help build the foundation for the development of hybrid cars (system with heterogeneous-ISAs in the same processor) in the future as well as the consideration of modifying existing car into a mega-car with multiple engines suited for different road needs for improved commute performance for now. Ultimately, this thesis is not about cars. The author hopes that by explaining the research done in this paper through cars, general audiences can understand what this work is trying to investigate and what solution they have provided. In this work, we investigate the potential of a system with heterogeneous-ISA processors. This thesis prototypes one such system and finds that heterogeneous-ISA systems have performance benefits than traditional homogeneous-ISA systems over a series of experiment evaluations.en
dc.description.degreeMaster of Scienceen
dc.publisherVirginia Techen
dc.rightsIn Copyrighten
dc.subjectSystem Softwareen
dc.subjectHeterogeneous Architecturesen
dc.titleLeveraging Processor-diversity For Improved Performance In Heterogeneous-ISA Systemsen
thesis.degree.disciplineComputer Engineeringen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.nameMaster of Scienceen


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