Browse Prior Art Database

Managing Exclusivity using an L2 Directory

IP.com Disclosure Number: IPCOM000105382D
Original Publication Date: 1993-Jul-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 63K

Publishing Venue

IBM

Related People

Rechtschaffen, R: AUTHOR

Abstract

The pattern exclusivity as relates to software of locks and the data these locks are protecting is clearly manifest in the L2 directory of a multiprocessing system. These "foot-prints" provide all the needed information to determine how the relinquishing of exclusivity should be managed. A special Memory Management Processor (MMP) associated with the L2 can perform the requisite store of sequences and the determination of repetitions in conjunction with the L2 directory so as to avoid unnecessary delays associated with logically incompatible software/hardware status.

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Managing Exclusivity using an L2 Directory

      The pattern exclusivity as relates to software of locks and the
data these locks are protecting is clearly manifest in the L2
directory of a multiprocessing system.  These "foot-prints" provide
all the needed information to determine how the relinquishing of
exclusivity should be managed.  A special Memory Management Processor
(MMP) associated with the L2 can perform the requisite store of
sequences and the determination of repetitions in conjunction with
the L2 directory so as to avoid unnecessary delays associated with
logically incompatible software/hardware status.

      It is in the nature of operating systems and hardware to
provide for redundant means to assuring consistency:

o   a software lock assures that only one processor at a time can
    access/update a particular datum through the use of a lock, and
o   a cache coherency protocol is maintained within a multiprocessor
    with a shared memory by restricting the update to cache lines to
    those held with EXCLUSIVE status.

Such uncoordinated actions often result in a physical manifestation
of a logical inconsistency.  Once a software lock is released, the
L1-cache lines whose update access is precluded because of the loss
of the lock  remain within the cache with an EXCLUSIVE status.  Thus,
the future owner of the lock must often await the relinquishing of
EXCLUSIVE status by a cache that can not logically access the datum
it holds EXCLUSIVE.

      The series of actions in which a process takes a software lock
and then accesses data that is protected by that lock are clea...