Need global explanation of the daemon

Patrick Ohly patrick.ohly at intel.com
Wed Nov 4 09:02:13 EST 2009


On Thu, 2009-10-29 at 10:09 +0000, Emmanuel Vargas wrote:
> I have a server sync on a GPS timeserver (meinberg) through NTPd.
> I want sync all my servers (appox 400 servers) to this servers through
> the ptpd daemon. I don't want to have the most accurate right time on
> all my server but I want to have exactly the same time on all my
> server!

Define "exactly"... Time synchronization is based on signal processing
and statistics, so there is no such thing as "absolutely exact"
synchronization, just varying degrees of accuracy.

> First question:
> Need a specific hardware?

It does help:
http://www.linuxclustersinstitute.org/conferences/archive/2008/PDF/Ohly_92221.pdf

Whether it is required, depends on how exact you want PTPd to be.

> Need a specific drivers for my Intel Pro 1000 network card?

Not for software-only PTPd. Hardware assisted PTP is not possible with
that hardware, as far as I know. The kernel igb driver does
hardware-assisted PTPd only with the 82576 GigE controller.

> I don't understand the
> <pre><code>(ptpd error) adjtimex -> time bad in the log</pre></code>

Use the source, Luke, eh, Emmanuel ;-) As far as I remember, this is the
result of the adjtimex() system call and didn't seem to have an effect
in my tests.

> and the
> <pre><code>(ptpd debug) offset from master:               0s       -1500ns </pre></code>
> (1500ns is a "time bad"? not sure to understand this...)

That's the time offset between master and slave as calculated by PTPd.
It should converge against zero.


-- 
Best Regards, Patrick Ohly

The content of this message is my personal opinion only and although
I am an employee of Intel, the statements I make here in no way
represent Intel's position on the issue, nor am I authorized to speak
on behalf of Intel on this matter.





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