Directory Schemes for Cache Coherence
Can’t see all Transactions made by other processors
- Means that we have to keep a list of which processors have a particular cache line, and explicitly send consistency commands to those processors
Keep a directory that contains an entry for each cache line
- Entry contains a list of pointers to all processors that hold this cache line
- Other status bits such as ‘valid’ and ‘write-permission’ are maintained as well.
Metrics for various directory schemes are amount of memory for directory, number of consistency commands (less is better)