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Acquisition of Data While Holding a Lock

IP.com Disclosure Number: IPCOM000105141D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

Rechtschaffen, R: AUTHOR

Abstract

In multiprocessing systems the operation within the memory hierarchy can be conditioned by the fact that the processor has acquired and not yet released a lock-word. This suggests that his subsequent actions within the hierarchy be made relative to that fact. In most operating systems, the data that might be shared erroneously is protected by both the hardware and the software. This form of double protection causes unnecessary delay that can be avoided.

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This is the abbreviated version, containing approximately 63% of the total text.

Acquisition of Data While Holding a Lock

      In multiprocessing systems the operation within the memory
hierarchy can be conditioned by the fact that the processor has
acquired and not yet released a lock-word.  This suggests that his
subsequent actions within the hierarchy be made relative to that
fact.  In most operating systems, the data that might be shared
erroneously is protected by both the hardware and the software.  This
form of double protection causes unnecessary delay that can be
avoided.

      The combination of hardware and software protection of data
that is shared and under lock management provides a set of prompts
that allows the hardware to properly handle situations that leave
relevant tracks in the memory hierarchy.

      Consider an Multiprocessing System that is implemented with a
memory hierarchy that is made up of a WI (Write In) L2 cache and
WTWAX (Write Through Write Allocate Exclusive) L1 caches.

      The problem with such a memory hierarchy concerns the exclusive
status of data following the final store to such data and the
reluctance to acquire data on an exclusive basis unnecessarily.  The
acquisition and retention of a lock-word changes this situation
especially if the release of the lock-word will relinquish the
exclusive status of all lines acquired while the lock was held.  The
action of acquiring a cache line on an exclusive basis if the line is
currently not held exclusive can be based on a bit maintained by the...