** Reply to message from Kanoj Sarcar [off-list ref] on Wed, 21
Jun 2000 13:49:56 -0700 (PDT)

Yes, this is saying that although we waste physical memory (which few
people care about any more), some of the unused space is never cached,
since it is not accessed (although hardware processor prefetches might
change this assumption a little bit). So, valuable cache space is not 
wasted that can be used to hold data/code that is actually used.

What I was warning you about is that if you shrink the array to the
exact size, there might be other data that comes on the same cacheline,
which might cause all kinds of interesting behavior (I think they call
this false cache sharing or some such thing).

Ok, I understand your explanation, but I have a hard time seeing how false
cache sharing can be a bad thing.

If the cache sucks up a bunch of zeros that are never used, that's definitely
wasted cache space.  How can that be any better than sucking up some real data
that can be used?



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Timur Tabi - ttabi@interactivesi.com
Interactive Silicon - http://www.interactivesi.com

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