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    Subject[REGRESSION 2.6.30][PATCH 0/1] sched: defer idle accounting till after load update period
    Date
    The following patch fixes a load avg calculation bug. Details are included with
    the patch. Essentially, a task that often runs for less than 10 ticks at a time
    is likely to be left out of the load avg calculation. A test case is provided
    below. If you run the test case on a near zero-load system you will find top
    report 90% cpu usage while the load avg stays at or near 0.00. With the patch,
    the load avg is calculated correctly to be at least 0.90.

    This is a regression since 2.6.30. The offending commit is:
    dce48a84adf1806676319f6f480e30a6daa012f9.

    --

    #include <asm/param.h>
    #include <sys/time.h>
    #include <time.h>

    int main() {
    struct timespec ts;
    ts.tv_sec = 0;
    ts.tv_nsec = 1000000000 / HZ;

    /*
    * Run gettimeofday in a tight loop 9 ticks, then sleep for 1 tick
    */
    while (1) {
    struct timeval tv;

    do {
    gettimeofday(&tv, NULL);
    } while ((tv.tv_usec * HZ / 1000000) % 10 != 0);

    nanosleep(&ts, NULL);
    }
    return 0;
    }


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