Re: Ktimer / -rt9 (+custom) monotonic_clock going backwards.

From: George Anzinger (george_at_mvista.com)
Date: 10/21/05

  • Next message: Grant Coady: "Re: 2.6.13.4: 'find' complained about sysfs" 
    Date:	Thu, 20 Oct 2005 15:19:29 -0700
To: Daniel Walker <dwalker@mvista.com>

    Daniel Walker wrote:
    > On Thu, 20 Oct 2005, Steven Rostedt wrote:
    >
    >>
    >> Yes, but that shouldn't make a difference. NTP can slow down or speed up
    >> the clock, but it should never make it go backwards. Especially for a
    >> monotonic clock (as the name suggests).
    >
    >
    > It looks like if ntp_adj held a big negative number you might end up
    > with a smaller output . ntp_adj is signed too .. I don't know how
    > ntp_adj is set though .
    >
    > I thought I remember George Anzinger speculating that ntp could
    > cause the time to backwards , that's why I brought it up. Maybe if he's
    > read he can clue us in ..
    >
    I think John has changed this, but in the "old" code if ntp was correcting the clock such that less
    than TICK_NSEC was added on a tick, AND, the time was read just prior to this tick the get_offset
    code would return ~TICK_NSEC of offset which would mean that a read right after the tick might be
    less than the one just prior to the tick. The error, however, would be in the nanosecond area (no
    where near a second). Again, as I said, I think John has changed this in is code so that the
    get_offset equivalent is also ntp corrected, thus eliminating the small back step.
    > 

    -- 
George Anzinger   george@mvista.com
HRT (High-res-timers):  http://sourceforge.net/projects/high-res-timers/
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  • Next message: Grant Coady: "Re: 2.6.13.4: 'find' complained about sysfs"

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