Efficient Exception Handling Support for GPUs

摘要

Operating systems have long relied on the exception handling mechanism to implement numerous virtual memory features and optimizations. However, today's GPUs have a limited support for exceptions, which prevents implementation of such techniques. The existing solution forwards GPU memory faults to the CPU while the faulting instruction is stalled in the GPU pipeline. This approach prevents preemption of the faulting threads, and results in underutilized hardware resources while the page fault is being resolved by the CPU. In this paper, we present three schemes for supporting GPU exceptions that allow the system software to preempt and restart the execution of the faulting code. There is a trade-off between the performance overhead introduced by adding exception support and the additional complexity. Our solutions range from 90% of the baseline performance with no area overheads, to 99.2% of the baseline performance with less than 1% area and 2% power overheads. Experimental results also show 10% performance improvement on some benchmarks when using this support to context switch the GPU during page migrations, to hide their latency. We further observe up to 1.75x average speedup when implementing lazy memory allocation on the GPU, also possible thanks to our exception handling support.