I've implemented a "lookaside" that's filled with 32K blocks that under most circumstances will never be used again. Clearly, here, the MVCLE with a Fill Character of X'B0' makes sense.
However, considering the rare circumstances when I do need to copy data back from the lookaside, I wonder if the X'B0' would make sense there as well. The source (cache) locations will again, probably never be referenced again. But, the target is a "recovery buffer" that will be referenced by other code, and there is a good chance that the data it currently holds is already in cache (from a previous usage). So, I guess part of my question is that when X'B0' is used as the fill character and all or part of the destination locations are in cache, are those cache lines updated or are they invalidated? If X'B8' is used as the fill character, how does operation differ from the use of, say, X'00' as the fill character? (The POps says simply, "a padding byte of B8 hex indicates an intention to reference the destination area" but says nothing about how the source area is handled with respect to the processor's cache. Thanks in advance for any insight, Art Celestini
