{"id":433,"date":"2023-11-21T08:00:40","date_gmt":"2023-11-21T08:00:40","guid":{"rendered":"https:\/\/christian-engelmann.de\/?page_id=433"},"modified":"2024-11-21T21:39:31","modified_gmt":"2024-11-21T21:39:31","slug":"xsim-the-extreme-scale-simulator","status":"publish","type":"page","link":"https:\/\/www.christian-engelmann.info\/?page_id=433","title":{"rendered":"xSim: The Extreme-scale Simulator"},"content":{"rendered":"\n\n
Summary:<\/b> The Extreme-scale Simulator (xSim) runs native high-performance computing applications with millions of concurrent execution threads in a controlled environment, while observing performance and resilience in a simulated extreme-scale system for application-architecture co-design. It is able to simulate a supercomputer with 134,217,728 (227<\/sup>) processes using a 960-core Linux cluster. It also offers process failure and soft error injection to study propagation, detection, notification and mitigation.<\/i><\/td>\n<\/tr>\n<\/table>\n

The path to exascale high-performance computing (HPC) poses several challenges related to power, performance, resilience, productivity, programmability, data movement, and data management. Investigating the performance and resilience of parallel applications at scale on future architectures and the performance and resilience impact of different architecture choices is an important component of HPC hardware\/software co-design. Without having access to future architectures at scale, simulation approaches provide an alternative for estimating parallel application performance and resilience on potential architecture choices. As highly accurate simulations are extremely slow and less scalable, different solution paths exist to trade-off simulation accuracy in order to gain simulation performance and scalability.<\/p>\n

The Extreme-scale Simulator (xSim) is a performance investigation toolkit that permits running native HPC applications or proxy applications in a controlled environment with millions of concurrent execution threads, while observing application performance and resilience in a simulated extreme-scale system for hardware\/software co-design. Using a lightweight parallel discrete event simulation (PDES), xSim executes a Message Passing Interface (MPI) application on a much smaller system in a highly oversubscribed fashion with a virtual wall clock time, such that performance data can be extracted based on a processor and a network model with an appropriate simulation scalability\/accuracy trade-off (Figure 1). xSim is designed like a traditional performance tool, as an interposition library that sits between the MPI application and the MPI library, using the MPI profiling interface (Figure 2). It has been run up to 134,217,728 (2^27) communicating MPI ranks using a 960-core Linux cluster (see Figure 3 for 2^24 results).<\/p>\n

xSim also permits the injection of MPI process failures, the propagation\/detection\/notification of such failures within the simulation, and their handling within the simulation using application-level checkpoint\/restart. These capabilities enable the observation of application behavior and performance under failure within a simulated future-generation HPC system using the most common fault handling technique. Another feature provides user-level failure mitigation (ULFM)<\/a> extensions at the simulated MPI layer to support algorithm-based fault tolerance (ABFT). This permits investigating performance under failure and failure handling of ABFT solutions using the fault-tolerant MPI extensions proposed by the MPI Fault Tolerance Working Group<\/a>. xSim is the very first performance tool that supports ULFM and ABFT.<\/p>\n

xSim also permits the injection of bit flip faults at specific of injection location(s) and fault activation time(s), while supporting a significant degree of configurability of the fault type. As radiation-induced bit flip faults are of particular concern in extreme-scale high-performance computing systems, xSim enables the development of soft-error resilient message passing applications by permitting the investigation of their correctness and performance under various fault conditions using this bit flip fault injection feature. xSim is the very first simulation-based MPI performance tool that supports both, the injection of process failures and bit flip faults.<\/p>\n\n\n
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\nFigure 1: xSim Architecture\n<\/td>\n		<\/td>\n\n
\nFigure 2: xSim Design\n<\/td>\n		<\/td>\n\n
\nFigure 3: Scaling a Monte Carlo code to 2^24 MPI ranks\n<\/td>\n		<\/td>\n<\/tr>\n<\/table>\n

Research Projects<\/h4>\n