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    Subject2.6.1 "clock preempt"?

    i've started to test the 2.6 series of kernels and observed a
    strange thing: with moderate background load, the system clock
    (i.e. time) seems to slow down to about 60% of normal speed
    and the normally reliable ntp process (v4.2.0)

    details: working interactively with a couple of background dummy
    processes (*1), my system clock slowed down approx 90 mins over
    a period of approx 4 hrs real time.

    (*1) infinite loop: 1 rip, 1 encode -- both run at nice 10

    the kernel logs show messages on the form:

    localhost kernel: Losing too many ticks!
    localhost kernel: TSC cannot be used as a timesource.
    (Are you running with SpeedStep?)
    localhost kernel: Falling back to a sane timesource.
    localhost kernel: set_rtc_mmss: can't update from 5 to 58

    without the background load, the system keeps perfect time.

    ==> any ideas of what could be going on would be appreciated.

    hardware details
    Intel P4 2.53gz on Supermicro P4SAA mobo (Intel 7205 chipset)
    1gb memory; multiple drives; Promise Ultra/133 raid controller
    kernel 2.6.1 w/APIC and PREEMPT options turned on.
    Fedora Core 1 + selected development packages (verified on 2.4).

    more info available on request.

    Steinar Hauan, dept of ChemE --
    Carnegie Mellon University, Pittsburgh PA, USA

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