Browse Prior Art Database

Avoidance of Delay on Lock-Protected Data

IP.com Disclosure Number: IPCOM000105273D
Original Publication Date: 1993-Jul-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 59K

Publishing Venue

IBM

Related People

Rechtschaffen, R: 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 54% of the total text.

Avoidance of Delay on Lock-Protected Data

      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.

      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 is that data remains
exclusive following the final store to such data.  In cases where the
access to such data is blocked by a software lock that assures that
only one processor can gain access to such data, a means can be
provided for the release of the exclusive status of the data to be
prompted by the release of the lock.  The benefit is that the
unnecessary overhead associated with releasing exclusive status be
avoided following such a software-lock protected data whose last
update has already occurred.

      ALGORITHM FOR RELEASE OF EXCLUSIVE STATUS - The pattern of
usage of COMPARE & SWAP instructions against memory locations within
a multiprocessor system can be used to select those COMPARE & SWAP
instructions that take a LOCK and release the LOCK.  It is assumed
that the software convention that will be used is that locks are
taken and released using COMPARE & SWAP instructions.  An alternate
approach to distinguishin...