Browse Prior Art Database

Selective Coherence Mechanism

IP.com Disclosure Number: IPCOM000112518D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Lawlor, FD: AUTHOR [+3]

Abstract

This invention describes a modified method for maintaining coherence in a computing system wherein coherence is maintained in the usual manner, but only on selected pages. This allows software to identify information requiring coherence to be maintained (by marking a control bit associated with each page). Allowing this "selective coherence" can result in a much lower load being placed upon the coherence mechanism thus lowering design cost and potentially improving performance.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 93% of the total text.

Selective Coherence Mechanism

      This invention describes a modified method for maintaining
coherence in a computing system wherein coherence is maintained in
the usual manner, but only on selected pages.  This allows software
to identify information requiring coherence to be maintained (by
marking a control bit associated with each page).  Allowing this
"selective coherence" can result in a much lower load being placed
upon the coherence mechanism thus lowering design cost and
potentially improving performance.

      A bit is defined which controls the action of the coherence
mechanism of the system.  The bit is defined to effect control over a
convenient unit of storage in the system, such as a page.  When the
bit is set on the coherence mechanism of the system operates in the
normal manner.  When the bit is set off no coherence checking or
tracking is done.

      The ability to selectively invoke the coherence function is
new.  It works with all current coherence implementation mechanisms.
Since references to shared storage typically represent only a small
portion of the total references, this invention dramatically reduces
the amount of information and the activity required to maintain
system coherence.  This allows many more processors to be combined in
a single system and minimizes the impact of sharing processors on
those which are not sharing.

      The selective coherence bit could be used to control coherence
in units other than a page...