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Hash Table Approach for the Recording of Information for XI Handling

IP.com Disclosure Number: IPCOM000120656D
Original Publication Date: 1991-May-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 68K

Publishing Venue

IBM

Related People

Liu, L: AUTHOR

Abstract

This article describes a facility for the recording of information useful for the handling of cross-interrogates for MP caches.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Hash Table Approach for the Recording of Information for XI Handling

      This article describes a facility for the recording of
information useful for the handling of cross-interrogates for MP
caches.

      In a tightly coupled MP design there is often useful
information that may guide the system to decide more optimal XI
strategies.  Examples are:
1.  Local-Change State (CHLoc) - Indicating whether a cache line has
been modified since it was last brought into the current cache, and
2.  XI Sensitivity - Indicating whether the line was encountered in
certain XI activities, for example, since the line was fetched into
the cache.

      Such information of cache lines that are useful for XI handling
either need not be put into individual (L1/L2) cache directory
entries, or may need to be put somewhere for the efficiency of
implementation.  In this invention, a Hash Table facility for the
recording of such information is described.  Such facility may be
shared by all CPs or may be used at each CP.

      First consider a single hash table at the SCE that is shared by
all CPs and is used to record CHLoc information. For any line L the
bit in the hash table associated with L is denoted by Hash(L).
Initially all bits in the hash table are OFF, indicating that none of
the lines has local changes.  When a line L is stored into by a CP,
the bit Hash(L) is turned ON.  Hash(L) is turned OFF (turned ON,
respectively) when L is first brought into a cache through a "fetch"
request ("store" request, respectively).  For a store-thru design it
is trivial how th...