GPU snapshot: checkpoint offloading for GPU-dense systems

Future High-Performance Computing (HPC) systems will likely be composed of accelerator-dense heterogeneous computers because accelerators are able to deliver higher performance at lower costs, socket counts and energy consumption. Such accelerator-dense nodes pose a reliability challenge because preserving a large amount of state within accelerators for checkpointing incurs significant overhead. Checkpointing multiple accelerators at the same time, which is necessary to obtain a consistent coordinated checkpoint, overwhelms the host interconnect, memory and IO band-widths. We propose GPU Snapshot to mitigate this issue by: (1) enabling a fast logical snapshot to be taken, while actual check-pointed state is transferred asynchronously to alleviate bandwidth hot spots; (2) using incremental checkpoints that reduce the volume of data transferred; and (3) checkpoint offloading to limit accelerator complexity and effectively utilize the host. As a concrete example, we describe and evaluate the design tradeoffs of GPU Snapshot in the context of a GPU-dense multi-exascale HPC system. We demonstrate 4--40X checkpoint overhead reductions at the node level, which enables a system with GPU Snapshot to approach the performance of a system with idealized GPU checkpointing.