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

[George Anzinger <george@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/