On 9/13/2010 11:54 PM, Joseph Gwinn wrote:
In article<1f42m7-7gr2@ntp.tmsw.no>,
Terje Mathisen<"terje.mathisen at tmsw.no"> wrote:
Joseph Gwinn wrote:
The address did not look munged to me either. It makes perfect sense for a
physicist to name servers after physics objects.
The standa
Miroslav,
I reached out to find nine NTP servers with known good pedigree, except
NIST. I found precissions ranging from -19 to -22, bu nothing better.
These included Sun UltraSPARC, Sun Blade, Intel dual-core, Intel Pentium
and ia64. They were running Linux 2.6, FreeBSD 6.1 and 8.0, SunOS 5.1
Dave,
I'm glad it's gone, as the code was never intended to measure
resolution. It is intended to measure precision, defined in the
specification as the time to read the system clock. This turns out to
be really important for a client to read two or more sources on the same
fast Ethernet. Th
On Thu, Sep 16, 2010 at 01:23:28AM +, David L. Mills wrote:
> The fastest machine I can find on campus has precision -22, or about
> 230 ns. Then, I peeked at time.nist.gov, which is actually three
> machines behind a load leveler. It reports to be an i386 running
> FreeBSD 61. Are you ready fo
On Thu, Sep 16, 2010 at 1:23 AM, David L. Mills wrote:
> Miroslav,
>
> The fastest machine I can find on campus has precision -22, or about 230 ns.
> Then, I peeked at time.nist.gov, which is actually three machines behind a
> load leveler. It reports to be an i386 running FreeBSD 61. Are you read
Miroslav,
The fastest machine I can find on campus has precision -22, or about 230
ns. Then, I peeked at time.nist.gov, which is actually three machines
behind a load leveler. It reports to be an i386 running FreeBSD 61. Are
you ready for this? It reports precision -29 or 1.9 ns! I'm rather
s
On Wed, Sep 15, 2010 at 01:34:04AM +, David L. Mills wrote:
> However, the ntpd
> measurements are after the clock filter and before the kernel call,
> while I suspect yours are after the discipline and before the kernel
> call. The two measurements are not comparable. Look at it this way.
> At
On Tue, Sep 14, 2010 at 07:17:04PM +, David L. Mills wrote:
> Miroslav,
>
> Better recalibrate your slide rule. On a 2.8 GHz dual-core Pentium
> running OpenSolaris 10, the measured precision is -21, which works
> out to 470 ns.
That probably just means the system on your machine is not using
Bill,
A feedback loop that minimizes time and frequency errors is a type-2
loop whether linear or not. NTP as specified and implanted is not
linear either, since it can use old samples in the clock filter
algorithmic, turns into a FLL at larger poll interval,. and has an
automatic poll-adjus
Miroslav,
Better recalibrate your slide rule. On a 2.8 GHz dual-core Pentium
running OpenSolaris 10, the measured precision is -21, which works out
to 470 ns. You claim ten times faster. What snake oil are you using for
your processor? To check, try running the jitter.c program in the
distrib
On Tue, Sep 14, 2010 at 02:45:01AM +, David L. Mills wrote:
> Don't get fooled by the MINSTEP. Precision is defined by the time to
> read the system clock at the user interface and I have never seen
> anything less than 500 ns for that, more typically 1000 ns.
This is what ntpd prints here (pa
On Tue, Sep 14, 2010 at 02:16:48AM +, David L. Mills wrote:
> Miroslav,
>
> I think we are talking right past each other. Both Chrony and NTP
> implement the clock discipline using a second-order feedback loop
> that can minimize error in both time and frequency, although each
> uses a differe
On 2010-09-14, David L. Mills wrote:
> Miroslav,
>
> I think we are talking right past each other. Both Chrony and NTP
> implement the clock discipline using a second-order feedback loop that
chrony does not use a second-order feedback loop it is a high order, and
variable order feedback loop.
On 2010-09-14, Joseph Gwinn wrote:
> In article <1f42m7-7gr2@ntp.tmsw.no>,
> Terje Mathisen <"terje.mathisen at tmsw.no"> wrote:
>
>> Joseph Gwinn wrote:
>> > The address did not look munged to me either. It makes perfect sense for a
>> > physicist to name servers after physics objects.
>> >
In article ,
unruh wrote:
> On 2010-09-13, Joseph Gwinn wrote:
> > Unruh,
> >
> > In article ,
> > unruh wrote:
> >
> >> On 2010-09-13, David L. Mills wrote:
> >>
> > [snip]
> >>
> >> > ... And, by the way, mail sent to your alleged mail address is
> >> > returned to sender as undeliverab
In article <1f42m7-7gr2@ntp.tmsw.no>,
Terje Mathisen <"terje.mathisen at tmsw.no"> wrote:
> Joseph Gwinn wrote:
> > The address did not look munged to me either. It makes perfect sense for a
> > physicist to name servers after physics objects.
> >
> > The standard approach is to put the demu
Miroslav,
You don't need a week for that, since the anticipated intercept is in
the order of 200 s (trace 3). However, plots such as these are really
susceptible to little hidden resonances, so I tend to prefer a long tail
and lots and lots of samples. For comparison, the averaging time for PP
Miroslav,
I think we are talking right past each other. Both Chrony and NTP
implement the clock discipline using a second-order feedback loop that
can minimize error in both time and frequency, although each uses a
different loop filter. Chrony uses a least-squares technique; NTP uses a
tradi
Joseph Gwinn wrote:
The address did not look munged to me either. It makes perfect sense for a
physicist to name servers after physics objects.
The standard approach is to put the demunging instructions in your sig. Like:
"Please remove reference to the entrance to a worm's burrow from email a
On 2010-09-13, Joseph Gwinn wrote:
> Unruh,
>
> In article ,
> unruh wrote:
>
>> On 2010-09-13, David L. Mills wrote:
>>
> [snip]
>>
>> > ... And, by the way, mail sent to your alleged mail address is
>> > returned to sender as undeliverable.
>>
>> Yes, I am sorry about that but it is done
Unruh,
In article ,
unruh wrote:
> On 2010-09-13, David L. Mills wrote:
>
[snip]
>
> > ... And, by the way, mail sent to your alleged mail address is
> > returned to sender as undeliverable.
>
> Yes, I am sorry about that but it is done in order to slightly reduce
> the spam I get. It shou
On Fri, Sep 10, 2010 at 08:48:58PM +, David L. Mills wrote:
> Miroslav,
>
> I've done this many times with several machines in several places
> and reported the results in Chapter 12 and 6 in both the first and
> second editions of my book, as well as my 1995 paper in ACM Trans.
> Networking.
On 2010-09-13, David L. Mills wrote:
> Bill,
>
> Please reread the definition of Allan deviation. It is a measure of
That makes no difference to the intercept and simply adds a constant slope of -1
to the graph. And note that the most common use of ntp is to discipline
the time, not the frequen
On Fri, Sep 10, 2010 at 10:10:08PM +, David L. Mills wrote:
> A previous message implied that, once the Allan characteristic was
> determined, it would show chrony to be better than ntpd. Be advised
> the default time constant (at 64 s poll interval) was specifically
> chosen to match trace 1 o
Bill,
Please reread the definition of Allan deviation. It is a measure of
frequency differences, not time errors. I principle, it could be applied
to a virtual machine with virtual timer interrupts, but nobody familiar
with the principles would do that and it would serve no useful purpose.
Th
On 2010-09-11, David L. Mills wrote:
> David,
>
> With due respect, your comment has nothing to do with the issue. Allan
> deviation is between a quartz crystal oscillator, timer interrupt,
> interpolation mechanism and a kerel syscall to read. the clock. It has
> nothing whatsoever to do with
"David L. Mills" wrote in message
news:4c8b9ab7.2050...@udel.edu...
> David Woolley wrote:
>> David L. Mills wrote:
>>> Running a precision time server on a busy public machine with a
>>> widely varying load is not a good idea and I have no interest in
>>> that.
>>
>> As indicated by the sort of
David,
I have no idea where you are coming from. At my feet are two GPS/CDMA
time servers running embedded Linux systems. I have two more on campus
plus two dedicated Unix machines connected to GPS receivers. NIST has
about a dozen dedicated time servers running FreeBSD. USNO has about a
doze
David,
With due respect, your comment has nothing to do with the issue. Allan
deviation is between a quartz crystal oscillator, timer interrupt,
interpolation mechanism and a kerel syscall to read. the clock. It has
nothing whatsoever to do with virtual machines.
Dave
David Woolley wrote:
David L. Mills wrote:
I beg to differ. All the machines I used are PCs or similar
workstations. They really and truly behave according to an exponential
As you note in another reply, you seem to use them in a way that is
abnormal for most users of NTP, i.e. as dedicated real machines in wel
David L. Mills wrote:
Bill,
Running a precision time server on a busy public machine with a widely
varying load is not a good idea and I have no interest in that. Running
As indicated by the sort of questions the group is getting recently, it
is becoming the norm to run time servers on virt
Bill,
Running a precision time server on a busy public machine with a widely
varying load is not a good idea and I have no interest in that. Running
experiments on a dedicated, but very busy, time server such as
rackety.udel.edu is much more interesting. As for load-induced
temperature variat
David,
I beg to differ. All the machines I used are PCs or similar
workstations. They really and truly behave according to an exponential
distribution with a small mean of a few to a few tens of microseconds. I
have done a tedious histogram from which I can pick out the cache
replacement, con
On 2010-09-10, David L. Mills wrote:
> This is a multi-part message in MIME format.
> --090107050005040702060208
> Content-Type: text/plain; charset=UTF-8; format=flowed
> Content-Transfer-Encoding: quoted-printable
>
> Miroslav,
>
> I've done this many times with several machines in s
Bill,
All my measurements were in temperature-controlled environments, such as
a campus lab or home office, and the data were collected over one week.
The temperature varied less than a degree C. However, I have data from
Poul-Henning Kamp for a similar experiment done in summertime Denmark
w
Miroslav Lichvar wrote:
A very useful statistics is the Allan deviation. It can be used to
compare performance of oscillators, to make a guess of the optimal
Surely that is based on a particular model of the phase noise and the
big argument about ntpd is that PC's don't follow that model.
_
Miroslav,
I've done this many times with several machines in several places and
reported the results in Chapter 12 and 6 in both the first and second
editions of my book, as well as my 1995 paper in ACM Trans. Networking.
Judah Levine of NIST has done the same thing and reported in IEEE
Trans
On Fri, Sep 10, 2010 at 04:05:29PM +, unruh wrote:
> Except yo uknow that the typical computer clock is driven mostly by
> temperature variations, and those are time of day dependent. People
> tend to work during the day thus their computer works during the
> day, and does not at night. Ie, the
On 2010-09-10, Miroslav Lichvar wrote:
> Hi,
>
> I'm trying to find out how a typical computer clock oscillator
> performs in normal conditions without temperature stabilization or a
> stable CPU load and how far it is from the ideal case which includes
> only a random-walk frequency noise.
>
> A
Hi,
I'm trying to find out how a typical computer clock oscillator
performs in normal conditions without temperature stabilization or a
stable CPU load and how far it is from the ideal case which includes
only a random-walk frequency noise.
A very useful statistics is the Allan deviation. It can
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