Cpu Design Questions
Cache coherence protocols in distributed shared memory systems are mechanisms designed to ensure that all copies of a shared memory location in different caches are kept consistent. In these systems, multiple processors or nodes have their own local caches, and when a processor modifies a shared memory location, it needs to notify other processors to update their copies.
Cache coherence protocols aim to maintain the illusion of a single shared memory by enforcing certain rules. These protocols define a set of actions and rules that processors must follow to ensure data consistency. The most common cache coherence protocols are the invalidation-based protocol and the update-based protocol.
In an invalidation-based protocol, when a processor modifies a shared memory location, it invalidates all other copies of that location in other caches. This means that other processors must fetch the updated value from the main memory when they access the shared location again.
In an update-based protocol, when a processor modifies a shared memory location, it updates all other copies of that location in other caches. This ensures that all caches have the most up-to-date value of the shared location.
Cache coherence protocols use various techniques such as snooping, directory-based schemes, or a combination of both to maintain coherence. Snooping involves each cache monitoring the bus for any memory operations that may affect its cached data. Directory-based schemes use a centralized directory that keeps track of which caches have copies of a shared memory location.
Overall, cache coherence protocols play a crucial role in ensuring data consistency in distributed shared memory systems by coordinating the actions of multiple caches and processors.