Re: 2.4: why is NR_GFPINDEX so large?

Timur Tabi
2000-06-21T20:59:51Z

** Reply to message from Kanoj Sarcar <kanoj@google.engr.sgi.com> 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?

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

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