This may seem silly, but the directory is separate from the cache lines, right? (Meaning, it's not taking up some space on the cache line to keep track of the state of all the cache lines, right?)
My understanding is that directory allows for fast lookup and update of what information has been invalidated more efficiently because you can lookup directly what the state of the current cache line is, and if you need to communicate something, you know where to communicate it to rather than needing to tell everybody.
Update: Answered one of my own silly questions
lya
Directory-based vs. snooping-based cache coherence is an instance of the space-time tradeoff. By designating directory to cache lines, directory-based coherence uses additional space to avoid the inefficient broadcasting and high latency.
This may seem silly, but the directory is separate from the cache lines, right? (Meaning, it's not taking up some space on the cache line to keep track of the state of all the cache lines, right?)
My understanding is that directory allows for fast lookup and update of what information has been invalidated more efficiently because you can lookup directly what the state of the current cache line is, and if you need to communicate something, you know where to communicate it to rather than needing to tell everybody.
Update: Answered one of my own silly questions
Directory-based vs. snooping-based cache coherence is an instance of the space-time tradeoff. By designating directory to cache lines, directory-based coherence uses additional space to avoid the inefficient broadcasting and high latency.