perfctr questions

[bert hubert <ahu@ds9a.nl>]

Mikael,

I'm trying to test your performance counters stuff, but I can't get it to do
anything remotely useful! Probably just me.

I have a very hard time understanding things like:

 *      perfex -e 0x00039000/0x04000204@0x8000000C some_program
 *
 *      Explanation: Program IQ_CCCR0 with required flags, ESCR select 4
 *      (== CRU_ESCR0), and Enable. Program CRU_ESCR0 with event 2
 *      (instr_retired), NBOGUSNTAG, CPL>0. Map this event to IQ_COUNTER0
 *      (0xC) with fast RDPMC enabled.

I'd love to author a small perfctr howto for people like me who just want to
know if their code is thrashing the cache. 

Do you have a pointer to tools that do this, or, how to calculate these
0x00039000 numbers for perfex? I can't find anything relevant. The best
information I found is in the 'hardmeter' sources.

I tried one very basic thing, perfex -e 0x00410005 ./null which I hoped
would measure unaligned memory accesses, but I can't get this counter raised
from 0. null.c:

int main(int argc, char **argv)
{
        char room[12];
        int i, n;

        for(n=0;n<1000000;++n) {
                i=*((int*)(room+n%4));  
        }
        
        printf("%d\n", i);
}

I'm on a Pentium M, 2.6.7-mm5. Not even sure if an Pentium M will measure
cache misses though.

Thanks

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