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ask

Would a multilevel directory based coherence protocol (analogous to multilevel page tables) be an effective solution for a scaling the directory based protocol to a large number of processors?

eosofsky

@ask - I was thinking this as well. If I understand correctly, using a multilevel directory based coherence protocol would allow for invalidation to be done in parallel (while the linked list strategy requires invalidation to be done serially). However, I think that such a solution would increase the memory overhead.

sstritte

To recap:

  • Limited pointer schemes take advantage of the fact that the data is probably only in a few caches at once.

  • Sparse directories take advantage of the fact that most of memory is not resident in the cache, and the coherence protocol only needs to worry about sharing information for lines that are currently in cache.