Browse Prior Art Database

Coordinating the Exclusivity Buffer with Locks

IP.com Disclosure Number: IPCOM000105082D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 68K

Publishing Venue

IBM

Related People

Rechtschaffen, R: AUTHOR

Abstract

The L2-CACHE can manage the exclusive status of lines in the L1 caches within a WTWAX system by use of an exclusivity buffer with limited capacity. The coordination of this buffer with lock/exclusivity control is disclosed.

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Coordinating the Exclusivity Buffer with Locks

      The L2-CACHE can manage the exclusive status of lines in the L1
caches within a WTWAX system by use of an exclusivity buffer with
limited capacity.  The coordination of this buffer with
lock/exclusivity control is disclosed.

A WTWAX cache management protocol is defined as:

o   all stores are written through the L1 cache to the L2 (WT),

o   all lines that are stored into by the processors must we
    allocated (WA - WRITE ALLOCATE), and

o   all lines written into must be held exclusively (X).

      THE EXCLUSIVITY BUFFER (EXB) - As all stores are written
through and all lines that are stored into must be held with
exclusive status, one means of managing prolonged and unnecessary
exclusivity, within the the set of L1-WTWAX caches, is to maintain a
buffer of line addresses for such lines and age lines out based on:

o   needs to add new exclusive lines, and

o   recency of last store update.

      This buffer or cache of addresses is called the EXCLUSIVITY
BUFFER (EXB).  As lines age out of the EXB they relinquish their
exclusivity.  A special treatment of stores to such lines might be
afforded if the lines have been identified as ping-pong lines, that
is, lines that will move between caches with high frequency.

      MANAGING EXCLUSIVITY WITH LOCKS - Another subclass of lines
that are held with EXCLUSIVE status are lines that have been made
exclusive while the processor held a lock.  A means of associating
this exclusivity with the holding of a lock creates a different means
of relinquishing exclusivity on a timely basis.  When the lock is
released, the algorithm of management of exclusivity relative to
lines that acquire exclusivity while the lock is held, is to
relinquish the exclusive status of such lines except in special
circumstances.

      COORDINATING THE EXCLUSIVITY BUFFER WITH...