Method and system for speculatively invalidating lines in a cache

A method of speculatively invalidating a line in a cache, the method comprising:

• accepting a request that results in the line in the cache being invalidated;
• initiating checks that determine whether or not the invalidation is erroneous;
• in response to said accepting, speculatively invalidating the line, wherein said
• speculatively invalidating comprises indicating that the line is invalid and protecting the line from subsequent modification until the checks have completed, and wherein in response to said accepting, said protecting further comprises not accepting additional requests that depend on data in or a state of the speculatively invalidated line until the checks have completed;
• in response to one of the checks determining that the invalidation is erroneous, reversing the speculative invalidation by indicating that the line is valid.

A method of speculatively invalidating a first cache line in an exclusive cache, the method comprising:

• accepting a fill request from a higher-level cache;
• determining whether the fill request hits in the exclusive cache;
• initiating checks that determine whether the fill request initiated erroneously;
• in response to the fill request hitting in the exclusive cache, providing the first cache line from the exclusive cache to the higher-level cache and, if the checks have not yet completed, speculatively invalidating the first cache line in the exclusive cache, wherein said speculatively invalidating comprises indicating that the first cache line is invalid and protecting the first cache line from subsequent modification until the checks complete;
• and
• in response to one of the checks related to the fill request determining that the fill request initiated erroneously, reversing the speculative invalidation of the first cache line.

A cache subsystem comprising:

• a cache comprising a plurality of cache line storage locations;
• and
• a cache controller coupled to receive a first request and configured to speculatively invalidate a first cache line in a first cache line storage location in response to receiving the first request, wherein the cache controller is further configured to reverse the speculative invalidation of the first cache line if the speculative invalidation is detected to be erroneous, wherein detecting whether the speculative invalidation is erroneous takes a number of cycles;
• and
• a speculative invalidation controller configured to protect the first cache line from modification for the number of cycles in response to the cache controller speculatively invalidating the first cache line, wherein the speculative invalidation becomes non-speculative after the number of cycles;
• wherein the speculative invalidation controller is further configured to prevent the cache controller from accepting additional requests that modify or depend on the speculatively invalidated first cache line for the number of cycles.

A computer system comprising:

• a processor;
• a system memory;
• a cache coupled to the processor and comprising a plurality of cache line storage locations;
• and
• a cache controller coupled to receive a first request, wherein the cache controller is configured to speculatively invalidate a first cache line in a first cache line storage location in response to the first request, and wherein in response to speculatively invalidating the first cache line, the cache controller is further configured to prevent modification of the first cache line storage location until the invalidation of the first cache line becomes non-speculative;
• and
• an error detection unit configured to perform at least one check corresponding to the first request, wherein if the check is performed and does not detect any errors, the invalidation of the first cache line becomes non-speculative;
• wherein the cache controller is further configured to not accept requests that depend on a state of or depend on data in the first cache line until the invalidation of the first cache line becomes non-speculative.

A computer system comprising:

• a processor;
• a system memory;
• a cache coupled to the processor and comprising a plurality of cache line storage locations;
• and
• a cache controller coupled to receive a first request, wherein the cache controller is configured to speculatively invalidate a first cache line in a first cache line storage location in response to the first request, and wherein in response to speculatively invalidating the first cache line, the cache controller is further configured to prevent modification of the first cache line storage location until the invalidation of the first cache line becomes non-speculative;
• and
• an error detection unit configured to perform at least one check corresponding to the first request, wherein if the check is performed and does not detect any errors, the invalidation of the first cache line becomes non-speculative;
• wherein the cache controller is configured to not accept additional requests based on a type of each additional request and whether each additional request depends on or modifies the speculatively invalidated first cache line until the invalidation of the first cache line becomes non-speculative.

A method of speculatively invalidating a line in a cache, the method comprising:

• accepting a request that results in the line in the cache being invalidated;
• initiating checks that determine whether or not the invalidation is erroneous;
• in response to said accepting, speculatively invalidating the line, wherein said speculatively invalidating comprises indicating that the line is invalid and protecting the line from subsequent modification until the checks have completed, wherein said protecting comprises not accepting additional requests that match a first portion of a tag of the speculatively invalidated line;
• and
• in response to one of the checks determining that the invalidation is erroneous, reversing the speculative invalidation by indicating that the line is valid.

A cache subsystem comprising:

• a cache comprising a plurality of cache line storage locations;
• and
• a cache controller coupled to receive a first request and configured to speculatively invalidate a first cache line in a first cache line storage location in response to receiving the first request, wherein the cache controller is further configured to reverse the speculative invalidation of the first cache line if the speculative invalidation is detected to be erroneous, wherein detecting whether the speculative invalidation is erroneous takes a number of cycles, wherein the number of cycles comprises a number of cycles to complete alias checking on an event that initiated the first request;
• a speculative invalidation controller configured to protect the first cache line from modification for the number of cycles in response to the cache controller speculatively invalidating the first cache line, wherein the speculative invalidation becomes non-speculative after the number of cycles.

A cache subsystem comprising:

• a cache comprising a plurality of cache line storage locations;
• and
• a cache controller coupled to receive a first request and configured to speculatively invalidate a first cache line in a first cache line storage location in response to receiving the first request, wherein the cache controller is further configured to reverse the speculative invalidation of the first cache line if the speculative invalidation is detected to be erroneous, wherein detecting whether the speculative invalidation is erroneous takes a number of cycles, wherein the cache controller is further configured to protect the first cache line by detecting that a subsequent request overwrites the first cache line and, in response, forcing the subsequent request to overwrite a different cache line;
• and
• a speculative invalidation controller configured to protect the first cache line from modification for the number of cycles in response to the cache controller speculatively invalidating the first cache line, wherein the speculative invalidation becomes non-speculative after the number of cycles.