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Show 116 copied to perform unwinding is m1nimized if the task migrated is from a choice point late in the execution rather than early. S1milarly, less unwinding is needed in this situation. The average time for a task migration is likely to be somewhat higher, but not by a substantial amount. Because stack recovery can take place only on unshared areas, this alternative migration strategy could be expected to frustrate efforts to recover stack areas. The value of scp will always be the same as that of lcp, since both the local process and remote processes will try to execute tasks arising from the latest choice point. These tasks, on the other hand, can be expected to terminate more quickly, facilitating memory recovery. The trade-offs between a more efficient binding method, increased task migration, and altered stack-reclamation attributes requires more study. 5.3 The Potential Impact of Alternative Architectural Decisions Bop log is intended for use on a machine like the Butterfly, with many processors, a large distributed memory and an Omega interconnect. Beyond these basic assumptions, details of the architecture have a significant effect on Boplog's performance. If these aspects of the particular machine were different, how would Boplog's performance differ? 5.3.1 Faster Memory Because all memory references generated by the 68020 are routed through the PNC, local memory references are rather slow. If local memory were faster, execution speed would probably be better by about the same degree, even if remote memory reference time remained unchanged. This conjecture is based on the ratio between local and remote value cells examined. Since faster local memory would improve overall performance, the effect would be the same as that noted earlier for improved program efficiency. In short, switch contention can be expected to be higher, and the statistics more valid. |
