System and method for time window access frequency based caching for memory controllers

Abstract

A system and method for replacing cached data for a computer system utilizing one or more storage devices is disclosed. The storage devices are divided into a plurality of areas or bins. Each bin is preferably the same size. A Window Access Table (WAT) is an array stored in memory that contains all the time windows for each bin. Each time window holds a frequency value corresponding to the number of times the bin has been accessed during the time period corresponding to that time window. A hot spot algorithm is used to calculate a hot spot value hsf(x) for each bin based on its associated frequency values listed in the WAT. The hot spot algorithm uses scaling coefficients to weight the frequency values based on the time window. Each line in cache will therefore have an associated bin for which a hot spot value hsf(x) has been calculated. This data may be stored in a hot spot table. When data is retrieved from a storage in response to a cache miss, the memory controller will compare the hot spot value hsf(a) of the bin associated with the new data to the lowest hot spot value hsf(z) in the hot spot table. If hsf(z) is greater than hsf(a), then this indicates that bin (z), the bin with the lowest hot spot value is accessed more frequently than bin (a), the bin containing the retrieved data. Thus if hsf(z) is greater than hsf(a), then the cache line containing data from bin (z) will not be replaced. If hsf(a) is greater than hsf(z) then the new data from bin (a) will replace the cached data from bin (z).