Adaptive Prefetching for Device Independent File I/O

Device independent I/O has been a holy grail to OS designers since the early days of UNIX. Unfortunately, existing OS''s fall short of this goal for applications that rely on very predictable I/O latency, such as multimedia players. Although techniques such as caching and sequential read-ahead can help by eliminating I/O latency in some cases, these same mechanisms can increase latency or add substantial jitter in others. In this paper we propose a new mechanism for achieving device-independent I/O -- adaptive prefetching using application-supplied hints of access patterns. Adaptive prefetching actively monitors device performance and dynamically adjusts the amount of prefetching. Our experiments show device independence can be achieved: a Berkley MPEG player sees the same latency when reading data from local disk or NFS. Moreover, our approach reduces jitter by a factor of 40 over standard techniques.