CPU Performance Study for HEP Workloads with Respect to the Number of Single-core Slots

Abstract

Many common CPU architectures provide simultaneous multithreading (SMT). The operating system sees multiple logical CPU cores per physical CPU core and can schedule several processes to one physical CPU core. This overbooking of physical cores enables a better usage of parallel pipelines and doubled components within a CPU core. On systems with several applications running in parallel, such as batch jobs on worker nodes, the usage of SMT can increase the overall performance. In high energy physics (HEP) batch/Grid jobs are accounted for in units of single-core jobs. One single-core job is designed to utilize one logical CPU core fully. As a result, Grid sites often configure their worker nodes to provide as many single-core slots as physical or logical CPU cores. However, due to memory and disk space constraints, not all logical CPU cores can be used. Therefore, it can be useful to configure more single-core slots than physical CPU cores but fewer than logical CPU cores per worker node. We have extensively used and studied this strategy at the GridKa Tier 1 center. In this contribution, we show benchmark results for different overbooking factors of physical cores on various CPU models for different HEP workflows and Benchmarks.