Based on our measurements above we can compute the paging latency. For example, the elapsed time of FFT on 28 Mbytes of input is 208 seconds, while the user time is 78.5 seconds. The rest 129.5 seconds should be attributed to paging overhead induced by 6520 page-in requests and 7791 page-out requests. Thus, the average latency per request is or 9.05 ms. From these, 7.2 ms were spend transferring each page on the Ethernet, and the rest 1.85 ms were the average software latency per paging request.
Previous measurements have reported that an 8 KByte page takes about 45 ms over an Ethernet for each page-in . Of those 45 ms, 19 ms were spent on TCP overhead, 4 ms were spent on Mach IPC overhead, 7.2 ms were spend on the Ethernet, and the rest were spent on the computer's I/O bus. The total software latency of our implementation, is only 1.85 ms. The reason for this significant difference in performance is threefold:
In general, although our approach may have less flexibility than a full fledged user-level pager, it has much better performance. Moreover, our device-driver implementation provides better performance than traditional disk paging, while user-level implementations have not reported performance results to support similar claims .