Prefetch miss indicator for cache coherence directory misses on external caches

• US 7,395,375 B2
• Filed: 11/08/2004
• Issued: 07/01/2008
• Est. Priority Date: 11/08/2004
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: DeSota, Donald R., Lais, Eric N., Joersz, Rob
• Primary Examiner(s): Portka; Gary J
• Assistant Examiner(s): Choe; Yong J.
• Application Number:
  US10/983,350
• Publication Number:
  US 20060101209A1
• Time in Patent Office: 1,331 Days
• Field of Search: 711/137, 711/141, 711/146, 712/237
• US Class Current: 711/141
• CPC Class Codes: G06F 12/082 Associative directories G06F12/0822 takes precedence
• CPC Class Codes: G06F 2212/507 using speculative control

Abstract

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.

Claims

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.