Managing high-coherence-miss cache lines in multi-processor computing environments
View Patent ↗Cache lines in a multi-processor computing environment are configurable with a coherency mode. Cache lines in full-line coherency mode are operated or managed with full-line granularity. Cache lines in sub-line coherency mode are operated or managed as sub-cache line portions of a full cache line. A high-coherence-miss cache line may be placed in sub-line coherency mode. A cache line may be associated with a counter in a coherence miss detection table that is incremented whenever an access of the cache line results in a coherence request. The cache line may be a high-coherence-miss cache line when the counter satisfies a high-coherence-miss criterion, such as reaching a threshold value. The cache line may be returned to full-line coherency mode when a reset criterion is satisfied.
1. A method for cache management in a multi-processor computing environment, the computing environment including a cache configured to hold a plurality of cache lines, each cache line configurable with a coherency mode, the method comprising:
accessing a first cache line in a full-line coherency mode, wherein cache control logic associated with the cache is configured to operate or manage the first cache line in the full-line coherency mode with a full-line granularity, the accessing the first cache line resulting in a coherence request, wherein based on the accessing, incrementing a counter in an entry in a coherence miss detection table, the entry associating the counter with the first cache line;
determining that the first cache line is a high-coherence-miss cache line, wherein the determining that the first cache line is the high-coherence-miss cache line comprises determining that the incremented counter satisfies a high-coherence-miss criterion; and
based on the determining, placing the first cache line in a sub-line coherency mode, wherein the cache control logic is configured to operate or manage a plurality of sub-cache line portions of the first cache line in the sub-line coherency mode.
2. The method of claim 1 , further comprising:
receiving, from another requestor in the computing environment, a request for the first cache line, the request targeting a memory address within the first cache line;
selecting a first sub-cache line portion of the first cache line, the first sub-cache line portion associated with the memory address;
notifying the requestor that only a sub-cache line portion of the first cache line will be returned; and
returning to the requestor the first sub-cache line portion in response to the request.
3. The method of claim 1 , wherein the first cache line is a first-cache copy of the first cache line in a first cache, and wherein a second-cache copy of the first cache line in a second cache remains in the full-line coherency mode after the placing the first-cache copy in the sub-line coherency mode.
4. The method of claim 1 , wherein the entry further associates the counter with at least one cache line adjacent to the first cache line.
5. The method of claim 1 , wherein the entry further associates the counter with a hash value of a memory address associated with the first cache line.
6. A computer system for cache management in a multi-processor computing environment, the computing environment including a cache configured to hold a plurality of cache lines, each cache line configurable with a coherency mode, the computer system comprising:
a memory; and
a processor in communication with the memory, wherein the computer system is configured to perform a method, the method comprising:
accessing a first cache linein a full-line coherency mode, wherein cache control logic associated with the cache is configured to operate or manage the first cache line in the full-line coherency mode with a full-line granularity, the accessing the first cache line resulting in a coherence request, wherein based on the accessing, incrementing a counter in an entry in a coherence miss detection table, the entry associating the counter with the first cache line;
determining that the first cache line is a high-coherence-miss cache line, wherein the determining that the first cache line is the high-coherence-miss cache line comprises determining that the incremented counter satisfies a high-coherence-miss criterion; and
based on the determining, placing the first cache line in a sub-line coherency mode, wherein the cache control logic is configured to operate or manage a plurality of sub-cache line portions of the first cache line in the sub-line coherency mode.
7. The computer system of claim 6 , wherein the determining that the incremented counter satisfies the high-coherence-miss criterion comprises:
determining that the incremented counter has reached a threshold value.
8. The computer system of claim 6 , wherein the determining that the incremented counter satisfies the high-coherence-miss criterion comprises:
calculating a percentage, the percentage based on the incremented counter and a total number of coherence misses in the computing environment; and
determining that the percentage has reached a threshold value.
9. The computer system of claim 6 , wherein the method further comprises:
determining that a reset criterion associated with the counter is satisfied;
resetting the counter based on the determining that the reset criterion is satisfied; and
placing the first cache line in the full-line coherency modebased on the determining that the reset criterion is satisfied.
10. The computer system of claim 9 , wherein the reset criterion is selected from the group consisting of:
a period of time elapses;
a number of instructions complete; and
a cache line associated with the counter is cast out of the cache.
11. The computer system of claim 6 , wherein the entry further associates the counter with at least one cache line adjacent to the first cache line.
12. The computer system of claim 6 , wherein the entry further associates the counter with a hash value of a memory address associated with the first cache line.
13. A computer program product for cache management in a multi-processor computing environment, the computing environment including a cache configured to hold a plurality of cache lines, each cache line configurable with a coherency mode, the computer program product comprising:
a non-transitory computer readable storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method, the method comprising:
accessing a first cache linein a full-line coherency mode, wherein cache control logic associated with the cache is configured to operate or manage the first cache line in the full-line coherency mode with a full-line granularity, the accessing the first cache line resulting in a coherence request, wherein based on the accessing, incrementing a counter in an entry in a coherence miss detection table, the entry associating the counter with the first cache line;
determining that the first cache line is a high-coherence-miss cache line, wherein the determining that the first cache line is the high-coherence-miss cache line comprises determining that the incremented counter satisfies a high-coherence-miss criterion; and
based on the determining, placing the first cache line in a sub-line coherency mode, wherein the cache control logic is configured to operate or manage a plurality of sub-cache line portions of the first cache line in the sub-line coherency mode.
14. The computer program product of claim 13 , wherein the method further comprises:
receiving, from another requestor in the computing environment, a request for the first cache line, the request targeting a memory address within the first cache line;
selecting a first sub-cache line portion of the first cache line, the first sub-cache line portion associated with the memory address;
notifying the requestor that only a sub-cache line portion of the first cache line will be returned; and
returning to the requestor the first sub-cache line portion in response to the request.
15. The computer program product of claim 13 , wherein the first cache line is a first-cache copy of the first cache line in a first cache, and wherein a second-cache copy of the first cache line in a second cache remains in the full-line coherency mode after the placing the first-cache copy in the sub-line coherency mode.
16. The computer program product of claim 13 , wherein the method further comprises:
determining that a reset criterion associated with the counter is satisfied;
resetting the counter based on the determining that the reset criterion is satisfied; and
placing the first cache line in the full-line coherency modebased on the determining that the reset criterion is satisfied.
17. The computer program product of claim 16 , wherein the reset criterion is selected from the group consisting of:
a period of time elapses;
a number of instructions complete; and
a cache line associated with the counter is cast out of the cache.