Shared Castout Buffer
Original Publication Date: 1985-Aug-01
Included in the Prior Art Database: 2005-Feb-19
In a multiprocessing system the "Cross-Interrogate" phenomenon (XI) results when shared data are used relatively closely together by different CPUs. XI activities may cause high performance penalties, especially when the number of CPUs grows. Among the XI activities, the so called "XI Castouts" (which will be abbreviated as "CA" throughout the rest of this article) are the most costly. A CA results when a (local) CPU references a line that is in a (remote) cache of another CPU and is modified there. In order to maintain the consistency of data, such a line can be fetched into the "local" cache either directly from the remote cache (cache-to-cache transfer) or from the Main Storage (MS) after the line has been dumped to the memory from the remote cache.