cache block การใช้

• Writing back every cache block which is evicted is not efficient.
• This makes the processor to be the latest to update the cache block.
• The inclusive snoop filter keeps track of the presence of cache blocks in caches.
• However, the exclusive snoop filter monitors the absence of cache blocks in caches.
• This again makes the processor to be the latest to update the cache block.
• After supplying the data, the cache block is in the " S " state.
• Therefore, we use the concept of a Dirty bit attached to each cache block.
• After the data is modified, the cache block is in the " M " state.
• It means that the snoop filter knows the caches that have a copy of a cache block.
• Even though various protocols use different implementations for tracking cache blocks, however the concept of directory remains same.
• Thus it can prevent the caches that do not have the copy of a cache block from making the unnecessary snooping.
• In other words, a hit in the inclusive snoop filter means that the corresponding cache block is held by caches.
• On the other hand, a hit in the exclusive snoop filter means that no cache has the requested cache block.
• The cache blocks that are in use, are locked into physical memory to avoid it being paged out to disk.
• A "'shared line "'is also required to indicate whether a certain cache block is available in multiple caches.
• When a write request happens, the corresponding cache block is marked dirty; dirty cache blocks are written lazily to disk in the background.
• When a write request happens, the corresponding cache block is marked dirty; dirty cache blocks are written lazily to disk in the background.
• A snoop filter is based on a directory based structure and monitors all coherent traffics in order to keep track of the coherency states of cache blocks.
• The original Pentium 4 processor also had an eight-way set associative L2 integrated cache 256 KB in size, with 128-byte cache blocks.
• For example, bus architectures often perform cache directories which have agents ( directories ) that know which caches last had copies of a particular cache block.