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Low Memory Early Castout and Change Recording

IP.com Disclosure Number: IPCOM000038865D
Original Publication Date: 1987-Mar-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Emma, PG: AUTHOR [+5]

Abstract

The invention proposes a mechanism that provides additional protection against uncorrectable soft errors for a particular area of memory that has a high probability of containing critical system data. Soft cache errors can have a sever impact when they affect critical system control information. The effects of soft cache errors can be significantly reduced by recording the changes to lines in the cache on finer granularity and by changing the usual store-in write back policy. Trace studies reveal that by far the most vulnerable cache lines are found in the Prefix Area. These lines contain the "anchors" for many important system control block chains and have very high reference activity. A significant number of these lines are essentially in the cache all the time in environments caracterized by high soft error rates.

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Low Memory Early Castout and Change Recording

The invention proposes a mechanism that provides additional protection against uncorrectable soft errors for a particular area of memory that has a high probability of containing critical system data. Soft cache errors can have a sever impact when they affect critical system control information. The effects of soft cache errors can be significantly reduced by recording the changes to lines in the cache on finer granularity and by changing the usual store-in write back policy. Trace studies reveal that by far the most vulnerable cache lines are found in the Prefix Area. These lines contain the "anchors" for many important system control block chains and have very high reference activity. A significant number of these lines are essentially in the cache all the time in environments caracterized by high soft error rates. These heavily referenced lines are much more vulnerable than the "average" changed line resident in the cache. This invention provides a small stack of double word addresses in page 0 (9 bits each) and double words to maintain duplicate copies of changed double words in the lines in this range. Whenever a double word leaves this stack, the line containing the double word is cast out of the cache and that line's status is changed from exclusive changed to exclusive. This mechanism is provided in addition to other mechanisms such as those mentioned above. When a line is cast out, however, the castout is tri...