A Dynamic and Proactive GPU Preemption Mechanism Using Checkpointing

Abstract

The demand for multitasking GPUs increases whenever the GPU may be shared by multiple applications, either spatially or temporally. This requires that GPUs can be preempted and switch context to a new application while already executing one. Unlike CPUs, context switching in GPUs is prohibitively expensive due to the large context states to swap out. There have been a number of efforts on reducing the overhead of preemption, through reducing the context sizes or overlapping context switching with execution. All those techniques are reactive approaches, meaning that context switching occurs when the preemption request arrives. In this paper, we propose a dynamic and proactive mechanism to reduce the latency of preemption. We observe that kernel execution is almost always preceded by known commands in both CUDA and OpenCL implementations. Hence, a preemption can be anticipated before the actual request arrives. We study such lead time and develop a prediction scheme to perform an early state saving. When the actual preemption is invoked, an incremental update relative to the previous saved state is performed, much like the conventional checkpointing mechanism. Our design can also choose to drain or checkpointing dynamically and accurately according to the feature of kernels in the runtime. This design effectively reduces the stall time of the preempting kernel due to context switching by 58.6%. Moreover, through careful handling of the saved state, we can also reduce the overall size of saved state by an average of 23.3%, compared with a full context switching.