Browse Prior Art Database

Exclusivity Through DLAT Only-Copy Indication

IP.com Disclosure Number: IPCOM000036756D
Original Publication Date: 1989-Oct-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Emma, PG: AUTHOR [+6]

Abstract

Integral to store-completion, existing high-end (nonbroadcast) coherency schemes employ methods of obtaining exclusive ownership of lines. Within this context, the use of the term "exclusive ownership" implicitly includes (what amounts to) locking the line via formal hardware protocol. Such protocols guarantee adherence to a given storage architecture, but in-and-of themselves, the protocols superfluously (and with substantial overhead) ensure such adherence when indication of an "only copy" is locally available. Specifically, the local DLAT can indicate those mappings that are only held by the local processor, thus alleviating the need for the director to engage a formal protocol for ensuring store-completion to lines within a given page.

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

Page 1 of 2

Exclusivity Through DLAT Only-Copy Indication

Integral to store-completion, existing high-end (nonbroadcast) coherency schemes employ methods of obtaining exclusive ownership of lines. Within this context, the use of the term "exclusive ownership" implicitly includes (what amounts to) locking the line via formal hardware protocol. Such protocols guarantee adherence to a given storage architecture, but in-and-of themselves, the protocols superfluously (and with substantial overhead) ensure such adherence when indication of an "only copy" is locally available. Specifically, the local DLAT can indicate those mappings that are only held by the local processor, thus alleviating the need for the director to engage a formal protocol for ensuring store-completion to lines within a given page.

Let the DLAT entry include a bit that indicates a uniquely held mapping or "only copy." The remainder of this article describes the control of this bit.

First, consider the simple case where no processor runs with DAT-off. Then each entry in the key array can include an indication of exclusive residence in some DLAT. Since the key array must be accessed to satisfy any associated DLAT miss, the key array indications are inherently managed by the underlying process of DLAT misses. Stores may be issued to any line whose DLAT entry indicates "only copy"; no further restrictions apply.

Note that remotely held copies of such a line may exist within the system, but remote processors must incur DLAT misses prior to referencing the line. Ensuring coherency is possible in (at least) three ways: 1) all relevant lines are invalidated when a DLAT entry is replaced (this precludes remote copies of such lines), 2) all relevant lines are invalidated when a DLAT entry is created (rendering the existence of remote lines moot), and...