Speaker
Description
The CMS experiment relies on a complex software ecosystem for detector simulation, event reconstruction, and physics analysis. As data rates and detector complexity continue to rise, scaling this software efficiently across distributed resources has become essential. We present the extension of the CMS Software (CMSSW) into a fully distributed application, enabling a single logical workflow to span multiple processes running on one or more machines. This approach leverages MPI to efficiently exploit shared memory and high-speed interconnects - like InfiniBand and RoCE - with minimal changes to the existing CMSSW code. Data movement to and from GPU memory leverages RDMA, enabling these transfers to bypass the host CPU entirely when supported by the underlying hardware. The distributed execution model is implemented through a small set of lightweight CMSSW modules responsible for MPI setup, event data transfers, and tracking the application’s logical state. The latter is critical for the High Level Trigger (HLT), where real-time performance depends on the early rejection of events failing selection criteria. We demonstrate this distributed model on an HLT test stand running alongside the production system during the 2026 data-taking period, and compare its usability and performance with current HLT nodes and previous benchmarks.
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