Determing cache sizes -- request for testing

[Don]

bearophile wrote:
> Don:
>> To implement efficient memory-intensive operations (memcpy, array 
>> operations, matrix multiplication, etc), you really need to know the 
>> sizes of the data caches.
> 
> Your code is surely useful, but take a look at "cache oblivious data structures":
> http://en.wikipedia.org/wiki/Cache-oblivious_algorithm

Yes, it's a good approach, but it doesn't help for something like memcpy.

> I presume your code doesn't work at compile time,

Correct.

> so I presume you have to run your code once, save the results on disk, and then re-start the compilation to use those values to compute the tuning compile-time constants of the data structures :-)

No. That wouldn't be much use.
The cache size is simply used as a parameter at run-time. It's only the 
linesize which has a major impact on optimal code -- but it's 32 or 64 
bytes on every system which I know of. So it's possible to deal with it 
at compile time, too.

You can, in fact, just plug the L1 cache size into your cache-oblivious 
algorithm as the cut-off level, significantly improving performance.

> On this Intel the data looks almost correct (I have used the second version of your code), but there isn't level 3 cache, and the RAM size is 2 GB.

The value shown for L3 should be greater than the memory size, if there 
is no L2 cache. (you never fall out of the L3 cache). So it's correct.