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Browse Prior Art Database

Storing in Read-Only Cache Lines

IP.com Disclosure Number: IPCOM000099827D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 1 page(s) / 35K

Publishing Venue

IBM

Related People

Emma, PG: AUTHOR [+5]

Abstract

In machines with either store-in caches or store- through caches with a policy of obtaining exclusive use before storing, it is possible to store in a line for which exclusive access has not yet been granted and continue to process instructions, provided certain restrictions are obeyed.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 97% of the total text.

Storing in Read-Only Cache Lines

       In machines with either store-in caches or store- through
caches with a policy of obtaining exclusive use before storing, it is
possible to store in a line for which exclusive access has not yet
been granted and continue to process instructions, provided certain
restrictions are obeyed.

      Processors with store-in caches and some processor designs with
store-through caches require that an exclusive copy of the line to be
modified be held in the local cache. In such processors, a delay is
incurred for a store to a line that is in the local cache but not
in exclusive status. The processor is delayed to assure that any
memory consistency requirements, such as those of System/370, are
obeyed.  However, in this case, the processor can continue operation,
including fetching from locations in the read-only line that were
modified by the store request.  To assure proper operation, no
accesses (fetches or stores) are made to lines that are not held
exclusive in the local cache until the confirmation of exclusive
status for the recently modified line.  This includes the read-only
line that was modified.  That is, only the portion of the read-only
line that was completely changed by the instruction doing the store
operation may be accessed before confirmation of exclusive status for
the entire line has been granted.  In addition, no new lines may be
fetched into the cache.  With these restrictions, the processor may
continue t...