Browse Prior Art Database

A Method to Prefetch Branches from a Target Buffer

IP.com Disclosure Number: IPCOM000110150D
Original Publication Date: 1992-Oct-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 1 page(s) / 59K

Publishing Venue

IBM

Related People

Barreh, JI: AUTHOR [+3]

Abstract

Disclosed is a strategy for allowing the prefetch of instructions from a target buffer in order to improve the overall performance of a given system.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 61% of the total text.

A Method to Prefetch Branches from a Target Buffer

      Disclosed is a strategy for allowing the prefetch of
instructions from a target buffer in order to improve the overall
performance of a given system.

      The inability to prefetch branches off a target buffer limits
the optimal performance of a machine.  The machine may be considered
to be made up of: 1) an icache-unit (ICU), 2) a fixedpoint unit
(FXU), and 3) a floating-point unit (FPU).  In general, the ICU uses
target buffers to reduce the penalty associated with processing
branches.  If a branch is known taken but is not eligible for
dispatch, the ICU will prefetch the target address of the branch, if
possible, into a target buffer.  When the branch is finally eligible
for dispatch, the target buffer instructions can be transferred into
the sequential buffer of the ICU to be dispatched the next cycle.  In
general, prefetched branches take one less cycle than non-prefetched
branches. Non-prefetched branches require an additional cycle in
order to generate the target address of the branch.  Previous methods
did not allow branches to be prefetched from the target buffers.

      Branches in the target buffers are identified and prefetched if
certain conditions are met.  These conditions are:
      1) an unresolved branch is resolved taken OR a branch that is
prefetched and taken is dispatched.
      2) there is a branch instruction (BI) in the target buffers.
      3) the target a...