Recently, we have seen growing pressure to move highperformance workloads, such as HPC and AI, to cloud environments that offer more affordable and manageable infrastructure. These workloads require direct access to RDMA devices for high-performance communication. Device passthrough, however, violates the decoupling between the guest OS and the underlying hardware, making Live Migration (LM) extremely challenging [29, 38, 40, 42, 48].

For more than 30 years, Hot Interconnects (HotI) has been a venue for discussions on cutting-edge network products, innovations in the network ecosystem, and a venue for introducing new network products in both software and hardware. This tradition continues with the 31st edition of the conference and it is reflected in the engaging program we have planned for HotI 2024. This year will be an online-only event and we expect over 1000 participants from all over the world. In addition, we are proud to announce best paper awards to highlight the novel and impactful work that is part of this year's program.

Process management libraries and runtime environments serve an important role in the HPC application lifecycle. This work provides a roadmap for implementing a high-performance PMIx based software stacks and targets four performance-critical areas presenting novel codesigned solutions that significantly improve application performance during initialization and wire-up at scale.

System-level checkpoint-restart is a critical technology for long-running jobs in high-performance computing. Yet, only two approaches to checkpointing MPI applications continue to survive in wide use today. One approach is to use the kernel module-based BLCR in combination with an MPI checkpoint-restart service particular to the MPI implementation in use. Unfortunately, this lacks support for some important Linux system services such as SysV IPC (e.g., shared memory objects). A second approach has been to use the original 2009 DMTCP implementation (herein referred to as DMTCP-09) for transparent, system-level checkpointing. Unfortunately, DMTCP-09 lacked support for checkpointing many of the necessary features found by MPI in a modern batch environment. These include: ssh, the InfiniBand network, process migration (restarting an MPI application on different cluster nodes), and modified file path prefixes on restart (typically due to a changing current directory, mount points, library paths, etc.). This work presents DMTCP-PV, a new user-space transparent checkpointing system based on the concept of process virtualization. This approach separately models the state of each local or distributed subsystem while decoupling it from the core checkpointing engine. By separating these concerns, a domain expert can extend checkpointing into a new domain without any knowledge of the core checkpointing engine. This allowed DMTCP-PV to address the deficiencies noted above and many others. It is shown that the runtime overhead of DMTCP-PV is generally less than 1%, and the checkpointing time is dominated by the time to write an image file to stable storage.

The MPI all-to-all algorithm is a data intensive, high-cost collective algorithm used by many scientific High Performance Computing applications. Optimizations for small data exchange use aggregation techniques, such as the Bruck algorithm, to minimize the number of messages sent, and minimize overall operation latency. This paper presents three variants of the Bruck algorithm, which differ in the way data is laid out in memory at intermediate steps of the algorithm. Mellanox's InfiniBand support for Host Channel Adapter (HCA) hardware scatter/gather is used selectively to replace CPU-based buffer packing and unpacking. Using this offload capability reduces the eight and sixteen byte all-to-all latency on 1024 MPI Processes by 9.7% and 9.1%, respectively. The optimization accounts for a decrease in the total memory handling time of 40.6% and 57.9%, respectively.