Recent work demonstrated that speculative execution has the potential to greatly improve the performance of I/O-intensive applications, while overcoming the limitations of compiler-assisted prefetching approaches. However, the previous user-level design requires the implementation of a complex, architecture-specific binary modification tool, benefits only explicit-I/O applications that have been transformed by such a tool, and does not limit the overhead incurred by increased memory contention.
In this paper, we present an in-kernel design for capturing the benefits of speculative execution while overcoming these limitations. We demonstrate that, for explicit-I/O applications, a simple design which leverages existing operating system mechanisms delivers benefits comparable to the prior user-level design. We then show that specialized versions of standard OS mechanisms - a fast, preemptible reforking operation and directional copy-on-write - greatly increase the benefits provided to swapping applications. Finally, we demonstrate a mechanism for limiting speculative overhead, while not impeding beneficial speculative execution, by scheduling speculative executions based on their memory impact. Our experience in implementing and evaluating speculative execution within Linux suggests that providing speculative execution within an operating system can be both feasible and effective.
We would like to thank Garth Gibson, Khalil Amiri and the anonymous reviewers for providing many helpful comments that greatly improved the paper. We would also like to thank Angela Demke for making her I/O benchmark suite available to us.