MESIF protocol
Encyclopedia
The MESIF protocol is a cache coherency
and memory coherence
protocol developed by Intel for cache coherent non-uniform memory architectures. The protocol consists of five states, Modified (M), Exclusive (E), Shared (S), Invalid (I) and Forward (F).
The M, E, S and I states are the same as in the MESI protocol
. The F state is a specialized form of the S state, and indicates that a cache should act as a designated responder for any requests for the given line. The protocol ensures that, if any cache holds a line in the S state, exactly one (other) cache holds it in the F state.
In a system of caches employing the MESI protocol, a cache line request that is received by multiple caches holding a line in the S state will receive multiple responses. In a system of caches employing the MESIF protocol, a cache line request will be responded to only by the cache holding the line in the F state. This methodology can be used to reduce the time that the original requestor of the cacheline will receive the data response for the cacheline, while allowing the use of as few multicast packets as the network topology will allow.
For any given pair of caches, the permitted states of a given cache line are as follows:
Cache coherency
In computing, cache coherence refers to the consistency of data stored in local caches of a shared resource.When clients in a system maintain caches of a common memory resource, problems may arise with inconsistent data. This is particularly true of CPUs in a multiprocessing system...
and memory coherence
Memory coherence
Memory coherence is an issue that affects the design of computer systems in which two or more processors or cores share a common area of memory....
protocol developed by Intel for cache coherent non-uniform memory architectures. The protocol consists of five states, Modified (M), Exclusive (E), Shared (S), Invalid (I) and Forward (F).
The M, E, S and I states are the same as in the MESI protocol
MESI protocol
The MESI protocol is a widely used cache coherency and memory coherence protocol. It is the most common protocol which supports write-back cache...
. The F state is a specialized form of the S state, and indicates that a cache should act as a designated responder for any requests for the given line. The protocol ensures that, if any cache holds a line in the S state, exactly one (other) cache holds it in the F state.
In a system of caches employing the MESI protocol, a cache line request that is received by multiple caches holding a line in the S state will receive multiple responses. In a system of caches employing the MESIF protocol, a cache line request will be responded to only by the cache holding the line in the F state. This methodology can be used to reduce the time that the original requestor of the cacheline will receive the data response for the cacheline, while allowing the use of as few multicast packets as the network topology will allow.
For any given pair of caches, the permitted states of a given cache line are as follows:
| M | E | S | I | F | |
|---|---|---|---|---|---|
| M | |||||
| E | |||||
| S | |||||
| I | |||||
| F |