Author: Andrew Slough
Date: 08:12:16 08/20/04
Go up one level in this thread
On August 20, 2004 at 10:51:50, Robert Hyatt wrote: >On August 20, 2004 at 04:33:07, Tom Kerrigan wrote: > >>Now that AMD is selling two processors that are identical other than L2 cache >>size (Sempron has 256k, Athlon 64 has 512k) we have proof of Crafty's working >>set size: >> >>Sempron: 1,080,020 NPS >>Athlon 64: 1,080,230 NPS >> >>http://www.anandtech.com/linux/showdoc.aspx?i=2170&p=3 >> >>This should prove once and for all that Crafty's working set is < 256k and >>therefore that size of L2 cache has no effect on its performance (as long as >>it's >= 256k) and that main memory speed likely plays a trivial role >>performance-wise. >> >>I bring this up because of all of the long debates that have occurred in the >>past about the value of L2 cache, the speed of memory, and the working set size >>of chess programs. >> >>I have no doubt that Crafty uses a bunch of memory, but obviously not with >>enough temporal locality for it to matter one iota. >> >>-Tom > > >Your interpretation _could_ be seriously flawed. IE suppose its working set is >2mb? You can't conclude anything if that is true as both the 256K and 512K >would be thrashing equally. > >Only _real_ way is to test with larger sizes as well. I've done that up to 2mb >and saw improvement from 512 to 1024K and from 1024K to 2048K, on older xeons. There's a nice tool in the GPL 'valgrind' suite to do cache usage profiling. It's called 'cachegrind'. http://valgrind.kde.org/tools.html To quote from the description: "Cachegrind is a cache profiler. It performs detailed simulation of the I1, D1 and L2 caches in your CPU and so can accurately pinpoint the sources of cache misses in your code. It identifies the number of cache misses, memory references and instructions executed for each line of source code, with per-function, per-module and whole-program summaries. It is useful with programs written in any language. Cachegrind runs programs about 20--100x slower than normal."
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