Method and apparatus for prefetching branch history information

US7493480B2 · kind B2 · utility

Assignee

• International Business Machines Corporation · US

Inventors

• Philip G. Emma · Danbury, US
• Klaus J. Getzlaff · Schenefeld, DE
• Allan M. Hartstein · Chappaqua, US
• Thomas Pflueger · Echterdingen, DE
• Thomas R. Puzak · Ridgefield, US
• Eric M. Schwarz · Gardiner, US
• Vijayalakshmi Srinivasan · New York, US

Key dates

• Filing date: Jul 18, 2002
• Grant date: Feb 17, 2009
• Expiry date: Oct 29, 2023

Classification

• Technology area (CPC G): Physics
• CPC primary: G06F9/3806
• WIPO field: Computer technology
• WIPO sector: Electrical engineering

Abstract

A two level branch history table (TLBHT) is substantially improved by providing a mechanism to prefetch entries from the very large second level branch history table (L2 BHT) into the active (very fast) first level branch history table (L1 BHT) before the processor uses them in the branch prediction process and at the same time prefetch cache misses into the instruction cache. The mechanism prefetches entries from the very large L2 BHT into the very fast L1 BHT before the processor uses them in the branch prediction process. A TLBHT is successful because it can prefetch branch entries into the L1 BHT sufficiently ahead of the time the entry is needed. This feature of the TLBHT is also used to prefetch instructions into the cache ahead of their use. In fact, the timeliness of the prefetches produced by the TLBHT can be used to remove most of the cycle time penalty incurred by cache misses.