What is the cache coherence?

cache coherence is a natural problem that develops when the system data set is approached and more agents are changed. The primary area of ​​computer architecture, where this becomes a problem, is in multiprocessor computers. Each processor on a multiprocessor computer has its own cache that reads and stores information from the RAM memory (RAM). When two processors approach the same area of ​​memory, the cache coherence would be lost if certain measures were taken.

without cache coherence could not work a multiprocessor system. There are several methods that have been developed to solve this problem and avoid potential problems. There are three methods that are used to prevent loss of cache coherence. The data is placed in a part of the memory that is accessible to all processors. When the information that stored in this memory area is either updated by the systemit is.

Snooping requires the processor to monitor all approaches to memory sites that were stored in the cache. This allows the processor to know when the registration has occurred. They know when to write, the processor can update its cache.

snarfing is quite similar to snooping. Snarfing includes not only monitoring access to memory sites that has been stored, but also monitoring the actual information stored in memory. When memory is written, the cache can be updated using new information.

Coherence based on directory has a relatively high latency, resulting in slower processing. The zone width requirements allow coherence systems based on the directory to be practical in large applications of cache coherence. The ore mprocessors that the system uses, the more advantages can be used by the use of a coherence system based on the directory.

Snooping is a much faster method. This method requires a larger bandwidth than a directory -based access. This method is able to effectively use in systems that have relatively few processors.

Snarfing is usually not used as a method of maintaining the cache coherence. This is mainly because snirfing requires multiple resources compared to the methods of snooping and directory. In order to work a snirfing system, they must monitor memory addresses and data stored in these areas of memory. The amount of bandwidth and processing, which is this method, is undesirable for most applications to maintain the cache coherence.