Browse Prior Art Database

Hardware Primary Directory Entry Chain Maintenance

IP.com Disclosure Number: IPCOM000103835D
Original Publication Date: 1993-Feb-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 2 page(s) / 56K

Publishing Venue

IBM

Related People

Randolph, JC: AUTHOR

Abstract

A method for reducing average primary directory entry (PDE) chain search time by doing hardware PDE chain maintenance is disclosed. The hardware moves PDEs beyond a search threshold to the front of the PDE chain.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 62% of the total text.

Hardware Primary Directory Entry Chain Maintenance

      A method for reducing average primary directory entry (PDE)
chain search time by doing hardware PDE chain maintenance is
disclosed.  The hardware moves PDEs beyond a search threshold to the
front of the PDE chain.

      Virtual address machines use a Primary Directory (PD) to
convert virtual addresses to physical addresses used to access
storage.  Virtual addresses which hash to the same Hash Index Table
(HIT) are chained together in PDE chains.  Hardware searches these
PDE chains to find a virtual address match, which indicates the
physical address for that virtual address.

      Frequently accessed PDE's sitting at the end of long PDE chains
cause excessively high PDE chain search time.  A solution this
problem is to do maintenance on the PDE chains, moving more
frequently used addresses to the front of the chain.

      Refer to the figure to visualize the moving of the target PDE
to the front of the chain.  The PDE containing the virtual address
match is called the target PDE.  Hash marks indicate changed pointers
to accomplish the task.

      Hardware would save the following indexes used during the PDE
chain search process for later use if the PDE chain is to be
adjusted:

o   PD hash (this is the offset into the HIT)

o   Index to the 1st PDE (from the HIT)

o   Index to the PDE preceding the target PDE

o   Index to the PDE after the target PDE, or zeros if the target
    ...