Prefetch miss indicator for cache coherence directory misses on external caches
View Patent ↗A system, method and article of manufacture for reducing latencies associated with cache coherence directory misses on external caches in a shared distributed memory data processing system. A cache coherence directory is evaluated for possible prefetching of a directory entry into a directory cache. A prefetch miss indicator is set if the prefetch evaluation results in a directory miss. The prefetch miss indicator is consulted during subsequent processing of a memory block request corresponding to the directory entry. An accelerated snoop response action is taken if the prefetch miss indicator is set. The latency of a second lookup into the cache coherence directory, which would otherwise be required, is thereby avoided.
1. A method for reducing latency associated with cache coherence directory misses on external caches in a shared distributed memory data processing system, comprising:
evaluating a cache coherence directory for possible prefetching of a directory entry into a directory cache;
setting a prefetch miss indicator in response to said prefetch evaluation resulting in a directory miss;
consulting said prefetch miss indicator during subsequent processing of a memory request corresponding to said directory entry; and
taking an accelerated snoop response action without reevaluating said directory based on said prefetch miss indicator being set.
2. The method of claim 1 wherein said directory evaluating includes evaluating a full mapped directory.
3. The method of claim 1 wherein said directory evaluating includes evaluating a sparse directory.
4. The method of claim 1 wherein said setting of a prefetch miss indicator includes storing a tag for said directory entry.
5. The method of claim 1 wherein said setting of a prefetch miss indicator includes storing a tag for said directory entry in a prefetch miss buffer.
6. The method of claim 5 wherein said prefetch miss buffer comprises an addressable memory.
7. The method of claim 5 wherein said prefetch miss buffer comprises a storage register.
8. The method of claim 1 wherein said setting of a prefetch miss indicator includes setting a prefetch miss status indicator in said directory entry and storing said entry in said directory cache.
9. The method of claim 1 wherein said consulting of said prefetch miss indicator is performed by consulting a prefetch miss buffer in conjunction with consulting said directory cache.
10. The method of claim 1 wherein said consulting of said prefetch miss indicator is performed by consulting said directory cache to identify a directory entry having a prefetch miss status indicator.