[ntp:hackers] Does ntpd need to whine more ?
David L. Mills
mills at udel.edu
Tue Oct 4 02:44:30 UTC 2005
Discussion on poles and zeros for the PLL and FLL are in my May 1992
technical report "Modelling and Analysis of Computer Network Clocks."
While that analysis could be used as the basis of a specification, since
after all the fixed parameters were defined, I don't think the WG would
accept a standard expressed in that way. Not many in the client
population have background in feedback control systems, Bode plots or
However, the poll-adjust algorithm is more intricate; a precurser is in
my 1998 SIGCOMM paper, but simplified and improved since then. It is
vital that the loop dynamics, including the time constant and PLL/FLL
weights be standardized, at least on the midstream servers. I have lots
of practical experience on what happens if not.
I'm sorry you don't trust the simulator. It does include the entire
suite of software modules of the in-vivo article, with the only
difference the synthentic moise generators and scripts used to simulate
body blows. There is no way I could have refined the poll-adjust
algorithm with poll intervals to 36 hours without it.
I do not plead guilty for ignoring data documenting some sort of
misbehavior or other; in fact, I have drowned in it. All cases to date
have been the result of a bug on my part due to some extreme scenario I
didn't expect or predict. Some I found in simulation, others by painful
reconstruction of the scenario and rigorous testing. The beast is an
incredibly complicated interacting real-time program and I wouldn't be
surprised if more bugs were found.
I don't think it was you that started me on the nanokernel trail. The
PTTI paper was in 2000, but my records with OSF-1 go back to 1995. The
challenge was to refine the method to work with a SMP Alpha; the
nanoseconds were an afterthought when I realized the PCC residuals due
to oscillator wander required that precision.
I won't coment on your judgement about lack of progress. Depends on
where you look. Autoconfiguration and public key authentication caught
my eye. I thought it necessary to construct the code skeleton, flow
charts and test plans in order to support the specification project. I'm
not saying this stuff is progress at all, just that it and the book
consumed a lot of work that might otherwise been spent on algorithmic
Yes, the WG is a bunch of rubberstampers. That's what a specification
task force does. There are or course interesting issues that develop
from the dialog that might suggest future research agenda. YOur voice
would be a useful contribution to the activity.
Poul-Henning Kamp wrote:
> In message <43415079.6040803 at udel.edu>, "David L. Mills" writes:
>> Your tone is dissapointing, but I am not going to argue with you.
>> Please, and I am serious about this, take your reservations to the NTP
>> WG and be heard.
> If my tone is dissapointing (and/or dissappointed), then it is
> because I have tried at various intervals over the last decade to
> convince you that NTPD could do better and been told "it works great
> in my simulator" with no appearant willingness to listen to dissenting
> points of view, even when actual data is produced.
> I'm proud that I managed to persuade you to take the step from micro
> to nanoseconds but that seems to be as far as I could shift you.
> This lack of progress is also to a large degree why I have pulled
> out of active NTPD development and one of the reasons why I will
> not spend my own time/money on NTP WG: Just like the PPS-API WG, I
> expect it to be nothing but rubber stamping of the status quo with
> no real intention to let new research and results affect the existing
> code base.
>> You didn't read my message. The requirement to use a crafted discipline
>> algorithm applies only to an intermediate server with upstream sources
>> and downstream clients.
> It is still bogus to mandate one particular algorithm rather than
> set up requirements for the performance. A good place to start
> would be to document the pole/zero positions of the current code,
> something I have yet to see anywhere.
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