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Changing an Exclusive Request to a Fetch Request

IP.com Disclosure Number: IPCOM000112984D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 74K

Publishing Venue

IBM

Related People

Baldus, DF: AUTHOR [+6]

Abstract

The local coherence unit in our multi-node system has the responsibility to maintain cache coherence for its address space. It filters all requests to addresses in its memory block. When a request for exclusive rights to an address is received, the unit will determine whether or not the requesting device has the data. If not, the exclusive ownership request will be changed to a fetch with an ownership request. Data will be returned to the requestor along with an ownership grant.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 33% of the total text.

Changing an Exclusive Request to a Fetch Request

   NODE A                       NODE B
   -----------                 -----------
  |  Proc 0   |               |  Proc     |
  |           |___            |           |___
  | D0-Shared |   |           |           |   |
   -----------    |            -----------    |
                  |                           |
                  |                           |
   -----------    |            -----------    |
  |  Proc 1   |   |           |  Proc     |   |
  |           |___|           |           |___|
  | D0-Shared |   |           |           |   |
   -----------    |            -----------    |
                  |                           |
   -----------    |            -----------    |
  |  Memory   |   |           |  Memory   |   |
  |           |___|           |           |___|
  |           |   |           |    D0     |   |
   -----------    |            -----------    |
                  |                           |
   -----------    |            -----------    |
  | Coherence |   |           | Coherence |   |
  |           |___|           |           |___|
  |    Unit   |               |    Unit   |
   -----------                 -----------
        |                           |
        |___________________________|

Fig. 1: Processors 0 and 1 both have shared copies and both
        issue requests for ownership of the data.

      The local coherence unit in our multi-node system has the
responsibility to maintain cache coherence for its address space.  It
filters all requests to addresses in its memory block.  When a
request for exclusive rights to an address is received, the unit will
determine whether or not the requesting device has the data.  If not,
the exclusive ownership request will be changed to a fetch with an
ownership request.  Data will be returned to the requestor along with
an ownership grant.

      In our multi-node system, each node has an associated address
space.  Since data may be shared as well as cached in any node in the
system, it is the responsibility of the local coherence unit to track
all addresses that are cached in another node.  The local coherence
unit includes a cache directory which records these addresses as well
as which nodes have copie...