Method for reducing the number of coherency cycles within a dire

Details Method for reducing the number of coherency cycles within a dire Method for reducing the number of coherency cycles within a dire

1996-12-09

1998-09-15

Swann, Tod R.

Electrical computers and digital processing systems: memory

Storage accessing and control

Hierarchical memories

711145, 711119, 711120, 711130, G06F 1208, G06F 1214

Patent

active

058095365

ABSTRACT:
An improved method for performing state cache line replacement operations in a multiprocessor computer system including plurality if data cache memories, a shared system memory, a state cache memory, and employing a centralized/distributed directory-based cache coherency system for maintaining consistency between lines of memory within the shared system memory and the plurality of data cache memories. The method for performing state cache line replacement operations includes the steps of: establishing a default system memory line state of SHARED for lines of memory represented in said state cache memory; reading the system memory line state for a previously stored state cache entry prior to a replacement of said previously stored state cache entry, said previously stored state cache entry being associated with a line of memory stored in said shared memory and at least one data cache memory; and performing a castout operation to update the line of memory within said shared memory and assigning a data cache memory line state of SHARED to said line of memory in each data cache memory containing said line of memory if said system memory line state for said previously stored state cache entry is OWNED. Since most lines of memory are in a shared state prior to replacement, setting the default state to a shared state, rather than a uncached state, reduces the number of invalidate coherency operations which must be performed during state cache line replacements.

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