Martin Albrecht wrote:
> Hi there,
>
> in the thread
>
> http://is.gd/4EMT8
>
> David and I agreed that M4RI should have a better, more robust and cross-
> platform mechanism to check for cache sizes.
>
> Thus I wrote a little C program to check for the cache size using timings of
> random-ish memory access.
>
> The program is available at:
>
> http://sage.math.washington.edu/home/malb/cache.c
>
> On my Core 2 Duo and on my Opteron (both running Linux 64-bit) it does report
> correct sizes. So far so good. On sage.math it reports L3 cache size instead
> of L2 but I guess that this is probably what we want anyway (well, L2 is 3MB
> which I don't check explicitly since I only check powers of two)
>
> I'd appreciate if those people on this list who have different hardware or
> software (OSX, Solaris, PPC, Sparc) could compile the program and report back
> whether the program reports correct sizes for them. To compile and run:
>
> gcc -std=c99 -O3 cache.c -o cache
> ./cache
>
> Cheers,
> Martin
>
>
His is on an HP C3600 running HP-UX 11.11. The has is a single PA-8600
processor
running at 552MHz. The cache size is 1.5 MB.
drkir...@hawk:~$ ./cache
8 0.009 2.937
16 0.017 1.991
32 0.035 2.033
64 0.078 2.227
128 0.206 2.647
256 0.455 2.208
512 1.026 2.255
1024 6.598 6.431
2048 13.274 2.012
4096 29.296 2.207
8192 72.191 2.464
16384 272.085 3.769
32768 930.273 3.419
65536 2126.173 2.286
512 16384
It would appear this cache program is not particularly good at guess cache
sizes, but what is probably more important is that it is able to optimise the
code so it works best on a particular processor. It is pretty irrelevant what
it
thinks that processor may or may not be. It's more important it optimises
itself
to run well on that processor.
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