Dynamic write priority based on virtual write queue high water mark for set associative cache using cache cleaner when modified sets exceed threshold

摘要

A set associative cache is managed by a memory controller which places writeback instructions for modified (dirty) cache lines into a virtual write queue, determines when the number of the sets containing a modified cache line is greater than a high water mark, and elevates a priority of the writeback instructions over read operations. The controller can return the priority to normal when the number of modified sets is less than a low water mark. In an embodiment wherein the system memory device includes rank groups, the congruence classes can be mapped based on the rank groups. The number of writes pending in a rank group exceeding a different threshold can additionally be a requirement to trigger elevation of writeback priority. A dirty vector can be used to provide an indication that corresponding sets contain a modified cache line, particularly in least-recently used segments of the corresponding sets.

主权项

1. A memory controller comprising:
a virtual write queue containing writeback instructions for selected cache lines of a cache memory to be written to a system memory device wherein the cache memory logically organizes the cache lines into sets according to different congruence classes; and a cache cleaner which determines when a number of the sets containing at least one modified cache line is greater than a first predetermined threshold, and responsively elevates a priority of the writeback instructions; and after elevating the priority of the writeback instructions, further determines that a second number of the sets containing at least one modified cache line is less than a second predetermined threshold, and responsively lowers the priority of the writeback instructions.