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    SubjectTime warps with Linux (but only 0.01sec)
    Hi,

    There was some talk about the pentium do_fast_gettimeoffset() routine
    lately, and claimed that the timer would progress monotonously. Well,
    it does not, for me. With the following program

    #include <sys/time.h>
    #include <unistd.h>
    #include <stdio.h>

    int main()
    {
    struct timeval t, t_old;
    long i;

    timerclear(&t);
    for(i=0; i<100000000l; i++) {
    gettimeofday(&t, NULL);
    if(i>0 && t.tv_sec==t_old.tv_sec && t.tv_usec<t_old.tv_usec)
    printf("old=%d new=%d\n", t_old.tv_usec, t.tv_usec);
    t_old = t;
    }
    }

    I get:

    old=333624 new=323878
    old=343739 new=333872
    old=673699 new=663860
    old=163717 new=153859
    old=963688 new=953864
    old=183655 new=173884
    old=463701 new=453857
    ...

    As you can see, very rarely (mostly during heavy disk activity), but
    consistently with a difference of 0.01sec. Looking at the kernel
    source, I can't see how this can happen.

    Thanks,
    Wolfram.


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