[LinuxPPS] Linux issues discussed earlier this year.

[William S. Brasher]

On Wed, 29 Jul 2009, clemens at dwf.com wrote:

> Earlier this year at least two Linux issues were discussed that would
> contribute to better timekeeping.
> 
> There was the definition of STA_NANO in timex.h
> and the calculation of nanoseconds in some glibc routines.
> 
> This (and any other details) was discussed in a number of separate messages
> on this forum.
>  
> Was it ever put together anywhere???
>     I dont see it on our wiki.
> 
> My understanding of the situation is that the STA_NANO problem can be fixed
> by just copying the timex.h from a current kernel into /usr/include/linux.
> 
> What about the glibc?  Does someone have an updated copy sitting out somewhere 
> that we can copy (I really dont want to get involved with git if I can help it)
> and what about the kernel itself?  Does it have bad code?  I seem to recall
> that for a while it calculated nanoseconds by multiplying microseconds by 
> 1000.  sigh.
> 

See:
 http://sourceware.org/bugzilla/show_bug.cgi?id=9690

The current glibc-2.10.1 has the NANO related changes present.  It does 
not have the TAI changes, since an ABI change is required.  I haven't seen 
such a change show up on the glibc lists.


See:
 http://lkml.indiana.edu/hypermail/linux/kernel/0905.0/01282.html
  Adjust SHIFT_PLL to improve NTP convergence.

 http://lkml.indiana.edu/hypermail/linux/kernel/0906.1/04254.html
  ntp updates for 2.6.31


I find setting SHIFT_PLL to 2 on my linux-2.6 pps boxes makes them behave 
almost as well as linux-2.4 pps boxes.