[ntp:questions] Re: NTP clients not throttling back is this behaviour RFC compliant?

Hal Murray hmurray at suespammers.org
Wed Dec 3 10:24:12 UTC 2003


>My first thought was to keep the TSC counts corresponding to the last
>few PPS crossings around in an array in the kernel.  One would also
>keep a seconds since the epoch counter that got incremented once per
>second by the same PPS signal.
>
>Now that one has the past history of the TSC crossings one can lightly
>filter it and generate tics-per-second.  This would only have to be
>done once per second.  One would then multiply the TCS tics since the
>last PPS crossing by the tics_per_second to get the fractional seconds
>for the timestamp.  What does that come out to?  One multiply and
>addition for the timestamp?

I've been thinking of building a board with FPGA and GPS card.
The idea is that one read from the card would give you the
correct time stamp.

But reads over PCI are sloooow.  You might be able to
do a lot the other work while that read is happening.

I think we all agree that the main cost of processing a packet is
kernel overhead.  Yes, you can save a lot of cycles if you send
the packet back where it came from.  Are there interesting cases
where that isn't good enough?

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