Re: [GIT pull] ntp updates for 2.6.31

[john stultz <johnstul@us.ibm.com>]

On Tue, 2009-06-23 at 15:36 +0200, Ingo Molnar wrote:
> The PPS patches i've seen just export IRQ timestamps to user-space.
> 
> That is not very robust in my opinion when it comes to do time 
> approximations - to get quick, low-latency action and precise 
> measurements it's best to keep the critical path as short as 
> possible, and within a single source code repository: i.e. within 
> the kernel.
> 
> There's little policy really, other than setting some general 
> parameters. NTPd can still provide the raw _network time_ 
> timestamps, as that is probably best fetched by user-space and fed 
> to the kernel.

At some point that stops being NTP. NTP has quite a bit of userland
policy for filtering and managing a number of different network clocks
(other ntp servers, PPS sources, etc).

>From what you're describing (direct offset from a hardware time device
used to steer the clock directly in kernel), you might want to look at
the STP code in s390 (stp_sync_clock).

thanks
-john