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    SubjectKernel 2.6.27.7-9 for Suse 11.1 help required with CPU Clock freq/speed/ticks
    Date
    From
    Hi All,

    I know this is not email list for programming questions but it relates
    to Kernel as well, in fact relying on kernel. Could someone please
    through a light or guide me to the right direction.


    Problem Statement: High CPU clock speed/freq
    Requirement: Obtain a stable CPU clock ticks/speed/freq on
    Suse 11.1 with kernel 2.6.27.7-9
    Questions: Please refer to the bottom of this page
    Artifacts in Use:
    -----------------------------------
    OS: Suse 11.1
    GCC Version: 4.3.2 (Suse Linux) [gcc_4_3-brach revision
    141291]
    Kernel: 2.6.27.7-9
    Kernel Mods:
    * Un-check the Tickless option
    * Timer Frequency - 1000Hz
    * Preempt kernel

    Others 1
    -----------
    OS: Suse 10.2
    GCC Version: 4.1.2 20061115 (prerelease)(SUSE Linux)
    Kernel: 2.6.18.2-34-default
    Kernel Mods:
    * Preemptible Kernel
    (Low-Latency Desktop) (NEW)
    * Preempt The Big Kernel Lock
    (NEW)
    * Timer frequency (NEW) - 1000
    Hz (NEW)

    Others 2
    -----------
    OS: Suse 9.3
    GCC Version: 3.3.5 20050117 (prerelease)(SUSE Linux)
    Kernel 2.6.11.4-20a-default
    Kernel Mods: None

    I executed the following c++ code on the above stated builds

    CODE - file name test.cpp
    #include <signal.h>
    #include <sys/time.h>
    #include <iostream>
    #include <cstdlib>


    using namespace std;

    long long int counter = 0;
    struct timeval last_time;
    struct timeval curr_time;
    double dif = 0.0;
    double freq_sum = 0.0;
    double reps = 0.0;
    double freq_min = 99999.0;
    double freq_max = 0.0;
    long long int num_too_low = 0;

    void time_check(int data)
    {
    // work out the frequecy of the SIGALRMs
    ++counter;
    if (counter >= 1000)
    {

    // need to work out time since last 1000 ticks
    gettimeofday(&curr_time, NULL);
    dif = ((curr_time.tv_usec + curr_time.tv_sec * 1000000)
    - (last_time.tv_usec + last_time.tv_sec * 1000000));
    double freq = (counter / dif) * 1000000;

    freq_sum = ((freq_sum * reps) + freq) / (reps + 1) ;

    ++reps;
    cout << "Frequency = " << freq << " reps= " << dif / 1000000 <<
    endl;
    if (freq_min > freq) freq_min = freq;
    if (freq_max < freq) freq_max = freq;
    if (freq < 950)
    ++num_too_low;
    last_time = curr_time;
    counter = 0;
    }
    }

    int main (int argc, char * argv[])
    {
    cout << "go" /* << "\a \a \a" */ << endl;

    int res;
    gettimeofday(&last_time, NULL);
    struct sigaction action;

    struct itimerval timer_value;

    timer_value.it_value.tv_sec = 0;
    timer_value.it_value.tv_usec = 1;
    timer_value.it_interval.tv_sec = 0;
    timer_value.it_interval.tv_usec = 1;

    action.sa_handler = time_check;
    action.sa_flags = SA_NOMASK;
    sigemptyset(&action.sa_mask);

    sigaction( SIGALRM, &action, NULL);
    res = setitimer( ITIMER_REAL, &timer_value, NULL );
    if (res == -1)
    cout << "error in setitimer" << endl;

    cout << "Starting CPU Test program" << endl;
    // loop for a long time

    while (reps < 3000.0)
    {
    sleep(1);
    }
    cout << "average CPU frequency = " << freq_sum << endl;
    cout << "reps = " << reps << endl;
    cout << "Min = " << freq_min << " Max = " << freq_max << endl;
    cout << "number of low = " << num_too_low << endl;
    return 0;
    }

    Compiled the above code with "g++ -o test test.cpp"
    Run the above code with "./test"

    Observations:
    SUSE Version AVG. Frequency AVG. REPS
    Suse 9.3 999.xxx to 990.xxx reps > 1
    (on average)
    Suse 10.2 999.xxx to 998.xxx reps (1
    - 1.001)
    Suse 10.3 1000.xxx to 912.xxx reps (1 - 1.090)
    Suse 11.1 0 to 324263.xxx reps
    (-2e-0.6 upto 0.005112)

    Suse 11.1 - Options:

    - Turn off ACPI in options when booting with clock=tsc | clock=pit

    Observations for suse 11.1 with options acpi=off and clock=tsc |
    clock=pit

    SUSE Version AVG. Frequency AVG. REPS
    Suse 11.1 710.xxx to 999.xxx reps
    (1.37xx to 1.0002)

    Hardware used for Suse 11.1 - HP Pavilion Slimline s3821uk Desktop PC
    (NQ808AA) specifications - HP Home & Home Office products
    http://h10010.www1.hp.com/wwpc/uk/en/ho/WF10a/12454-12454-3329740-64546-
    64546-3884669.html?jumpid=in_r2515_uk/en/hho/ipg/psc404redirect-ot-xx-xx
    -/chev/

    While testing no other application/s were running.

    Question:

    * Is my c++ code correct?
    * Am I using the correct way to get the clock ticks or is there more
    reliable tchnique avaliable to do this?
    * Is that a problem with new Kernel if so is it a known issue ?
    * Do I need to modify the Kernel to obtain regular and stable clock tick
    at 1000 Hz ?
    * Do I have to upgrade the Kernel ?
    * Would be great, if pointed to the right direction for solution (e.g.
    another forum) if no solution at hand.

    Thanks

    Subhan

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