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    Subjectsmall perfctr bug or misunderstanding
    On Sat, Jul 03, 2004 at 12:28:09PM +0200, Mikael Pettersson wrote:

    > There would be a /proc/<pid>/<tid>/perfctr/ directory
    > with files representing the control data, counter
    > state, general info, and auxiliary control ops.

    Mikael, thanks for the low-level-api.txt documentation. Will vperfctr_* see
    some documentation? Want me to whip up manpages?

    So far perfctr has been very useful to me already - I now know parts of
    PowerDNS that are completely memory bound, which I so far only suspected.
    Are the global counters available? There is a note in the perfctl
    distribution that says they aren't?

    One thing - on my Pentium M I'm unable to get more than one counter going
    simultaneously, I get 'Operation not permitted'. Perfex reports that
    supposedly two are possible.

    PerfCtr Info:
    abi_version 0x06000500
    driver_version 2.7.3
    cpu_type 14 (Intel Pentium M)
    cpu_features 0x3 (rdpmc,rdtsc)
    cpu_khz 1399252
    tsc_to_cpu_mult 1
    cpu_nrctrs 2
    cpus [0], total: 1
    cpus_forbidden [], total: 0

    PERFCTR INIT: vendor 0, family 6, model 9, stepping 5, clock 1399252 kHz
    PERFCTR INIT: NITER == 64
    PERFCTR INIT: loop overhead is 118 cycles
    PERFCTR INIT: rdtsc cost is 48.5 cycles (3223 total)
    PERFCTR INIT: rdpmc cost is 45.4 cycles (3027 total)
    PERFCTR INIT: rdmsr (counter) cost is 95.4 cycles (6229 total)
    PERFCTR INIT: rdmsr (evntsel) cost is 81.3 cycles (5322 total)
    PERFCTR INIT: wrmsr (counter) cost is 143.7 cycles (9318 total)
    PERFCTR INIT: wrmsr (evntsel) cost is 132.3 cycles (8591 total)
    PERFCTR INIT: read cr4 cost is 3.0 cycles (311 total)
    PERFCTR INIT: write cr4 cost is 49.8 cycles (3308 total)
    perfctr: driver 2.7.3, cpu type Intel P6 at 1399252 kHz

    On my Athlon, 4 are reported possible and 4 work just fine. But I might be
    misunderstanding the Intel docs.

    The code below works fine when the second counter is commented out:

    #include <iostream>
    using namespace std;
    extern "C" {
    #include "libperfctr.h"
    }
    #include <errno.h>
    #include <stdlib.h>
    #include <stdio.h>
    #include <string.h>
    #include "arch.h"

    class PerfCtr
    {
    public:
    PerfCtr()
    {
    d_self = vperfctr_open();
    if( !d_self ) {
    perror("vperfctr_open");
    exit(1);
    }

    memset(&d_control.cpu_control, 0, sizeof(d_control.cpu_control));
    d_control.cpu_control.tsc_on=1;
    }

    void addCounter(unsigned int v, unsigned int unit=0)
    {
    int count=d_control.cpu_control.nractrs;

    d_control.cpu_control.evntsel[count] = v | (1 << 16) | (1 << 22) | (unit << 8);
    d_control.cpu_control.pmc_map[count] = count;
    d_control.cpu_control.nractrs++; // no support for .nrictrs
    }

    void go()
    {
    if(vperfctr_control(d_self, &d_control) < 0) {
    perror("vperfctr_control");
    exit(1);
    }
    zero();
    }

    void zero()
    {
    memset(&d_baseline,0,sizeof(d_baseline));
    vperfctr_read_ctrs(d_self, &d_baseline);
    }

    ~PerfCtr()
    {
    vperfctr_close(d_self);
    }

    void get(long long* counters, long long& tsc)
    {
    struct perfctr_sum_ctrs now;
    memset(&now,0,sizeof(d_baseline));
    if(vperfctr_read_ctrs(d_self, &now) < 0) {
    perror("read counters");
    exit(1);
    }

    for(unsigned int n=0;n<d_control.cpu_control.nractrs;++n)
    counters[n]=now.pmc[n] - d_baseline.pmc[n];

    tsc=now.tsc - d_baseline.tsc;
    }

    private:
    struct vperfctr *d_self;
    struct vperfctr_control d_control;
    struct perfctr_sum_ctrs d_baseline;
    };


    int main()
    {
    PerfCtr pc;
    pc.addCounter(0x48); // DCU MISS OUTSTANDING
    pc.addCounter(0x43); // DATA_MEM_REFS

    pc.go();

    long long results[2], tsc;
    pc.get(results,tsc);

    cout<<"Cycles waiting on DCU miss: "<<results[0]<<endl;
    cout<<"Number of memory references: "<<results[1]<<endl;
    cout<<"Cycles spent: "<<tsc<<endl;
    }



    --
    http://www.PowerDNS.com Open source, database driven DNS Software
    http://lartc.org Linux Advanced Routing & Traffic Control HOWTO
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