Comparing snooping to directories, snooping protocols tend to be faster since if enough bandwidth is available, all transactions are a message seen by all processors. However, snooping is not scalable. Each request has to be broadcast to all nodes in a system, meaning that as the system gets larger, the size of both the bus and the bandwidth it provides needs to grow for us to maintain speed.
Directories tend to have higher latencies (using more messages each write or read) but use much less bandwidth as messages are not broadcast to all processors but rather from one point to one point. Thus, many larger systems use directory based cache coherence.
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analysiser
So does it mean, according to the last sentence on this slide, if there are a lot of sharers trying to read and write data simultaneously, all caches are communicated at the same time, snooping based cache coherence could beat directory based coherence because it has fewer overhead of intercommunication and lower latency?
Comparing snooping to directories, snooping protocols tend to be faster since if enough bandwidth is available, all transactions are a message seen by all processors. However, snooping is not scalable. Each request has to be broadcast to all nodes in a system, meaning that as the system gets larger, the size of both the bus and the bandwidth it provides needs to grow for us to maintain speed.
Directories tend to have higher latencies (using more messages each write or read) but use much less bandwidth as messages are not broadcast to all processors but rather from one point to one point. Thus, many larger systems use directory based cache coherence.
This comment was marked helpful 0 times.
So does it mean, according to the last sentence on this slide, if there are a lot of sharers trying to read and write data simultaneously, all caches are communicated at the same time, snooping based cache coherence could beat directory based coherence because it has fewer overhead of intercommunication and lower latency?
This comment was marked helpful 0 times.