Re: [NTP 8/9] convert to the NTP4 reference model

From: Roman Zippel
Date: Thu Aug 17 2006 - 07:02:15 EST


On Thu, 10 Aug 2006, linux@xxxxxxxxxxx wrote:

> The original NTP kernel interface was defined in units of microseconds.
> That's what Linux implements. As computers have gotten faster and can
> now split microseconds easily, a new kernel interface using nanosecond
> units was defined ("the nanokernel", confusing as that name is to OS
> hackers), and there's an STA_NANO bit in the adjtimex() status field to
> tell the application which units it's using.

BTW this patch didn't add the STA_NANO bits yet, as that requires changes
to <sys/timex.h> and a recompiled ntpd, so the values are still in usec.
It's not difficult to change/add, but one has to be a little careful about

> The current ntpd supports both, but Linux loses some possible timing
> resolution because of quantization effects, and the ntpd hackers would
> really like to be able to drop the backwards compatibility code.
> Ulrich Windl has been maintaining a patch set to do the conversion for
> years, but it's hard to keep in sync.

I think you refer to the PPSKit? Well, the first step to integrate it
properly is done. Ulrich took the reference code rather unmodified, which
has a rather strong emphasis on weird portability (one only has to look at
l_fp.h to know what I mean), which is not really acceptable in the kernel.
Its ioctl API probably should be converted to sysfs, so there is still
some way to go.

bye, Roman
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