Browse Prior Art Database

Cache Interrogation with Partial Address Directory

IP.com Disclosure Number: IPCOM000105350D
Original Publication Date: 1993-Jul-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 76K

Publishing Venue

IBM

Related People

Liu, L: AUTHOR

Abstract

Proposed is a technique to filter cache interrogations with partial address directories. Such technique avoids majority of unnecessary cache interrogates with reduces hardware as compare with with conventional methods.

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

Cache Interrogation with Partial Address Directory

      Proposed is a technique to filter cache interrogations with
partial address directories.  Such technique avoids majority of
unnecessary cache interrogates with reduces hardware as compare with
with conventional methods.

      In modern computers a cache often needs to be interrogated.
Examples are: 1) An I-cache line needs to be invalidated when
modified by the processor (to the D-cache) in an I/D-split cache
design; and 2) A cache line at a processor needs to be invalidated
when modified by a remote processor or I/O channel.  It is important
to properly filter such cache interrogations.  An ideal situation is
for a cache to get interrogated (e.g., for invalidate) only when
necessary (e.g., when it has a line being written remotely).  A
common technique for such filtering is to employ copy directory.  For
instance, at a processor with I/D-split caches, a copy directory of
the I-cache (separate from the usual I-cache directory) may be
utilized for store invalidate interrogations, so that I-cache
directory cycles will not be wasted for occasional stores to I-cache.
Another example is the popular snoopy-cache design for
multiprocessors, in which each processor has a cache directory copy
that handles all the store-interrogates (e.g., remote processor
stores) from the common-bus.

      On problem associated with the above copy directory schemes is
the amount of circuits required.  Such problem is more serious when
the cache gets larger or when more addressing-bits are involved.

      The current invention utilizes partial address directories as a
filtering device that can eliminate majority of unnecessary cache
interrogates, which with reduced circuits compared with conventional
copy directories.  The basic idea is to utilize a Partial Address
Copy Directory (PACD) to filter interrogates to the cache.  The
structure of PACD is similar to descriptions in prior art with
partial address bits recorded at each directory entry.  The
congruence class selection is via full address as usual, while
directory lookup is done via p...