** Reply to message from Kanoj Sarcar [off-list ref] on Wed, 21
Jun 2000 14:10:17 -0700 (PDT)

Okay, I will shut up since I will have to pull out old notes and books
to convince you, but basically, here's a simple example. Say a L2 cache 
line is 128 bytes, and each array element is 16 bytes, giving 8 array 
elements per cache line. Say you decide to eliminate the last element,
maybe because it is not used. So, in that space, two global integers/
spinlocks etc are packed in after the deletion. Further assume these
two integers are frequently updated. Looking at an SMP system that uses
the exlusive write cache update protocol, the cache line will probably
bounce between the different L2 caches, which is quite bad, assuming 
that the original 8 element array was readonly, and was probably 
coresident in all the caches.

Fascinating.  I really appreciate your taking the time to explain this to me.  

So I suppose the best way to optimize this is to make sure that "NR_GFPINDEX *
sizeof(zonelist_t)" is a multiple of the cache line size?



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

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