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Browse Prior Art Database

Relinquishing Exclusivity on Targets of Successful Compare and Swap

IP.com Disclosure Number: IPCOM000106038D
Original Publication Date: 1993-Sep-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

R. Rechtschaffen: AUTHOR

Abstract

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 approach to avoiding this delay is detailed.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 66% of the total text.

Relinquishing Exclusivity on Targets of Successful Compare and Swap

      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 approach to avoiding this delay is detailed.

      Another mismatch between hardware and software is associated
with the taking of locks.  The intent here is that other processors
be able to determine that the lock is taken and the holding of the
lock exclusive creates additional overhead.

      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 acquisition of a software lock as a prerequisite for
accessing sharable data is to assure that operation of critical
sections within the software will be serialized between multiple
processors.  If the lock is acquired via  a COMPARE & SWAP
instruction which is successful then the lock-word is held exclusive
in the cache of the processor which does not require the knowledge
that the lock is held.  Other processors attempting to acquire the
lock will be forced to wait for the exclusive status to be rescinded
before they determine that the lock is unavailable.  With higher
levels of multiprocessing the likelihood that the processor which
took the lock would benefit from hold the lock-word exclus...