[ntp:questions] NTP vs RADclock?

Rick Jones rick.jones2 at hp.com
Fri Jun 8 20:14:30 UTC 2012


unruh <unruh at invalid.ca> wrote:
> This is a rare thing (Ie once in a 100 packets has round trip delay
> of 10ms, vs 10us usually.) I have no idea if this is interrupt
> coalescing or what. Since our network switched to Gigabit switches
> and some of my systems use gigabit cards, the timing behaviour has
> become really bad.

> It used to be that I got consistant 140us round trip delays ( with a
> scatter of about 10-20us) Now, although that is still the minimum,
> all have a scatter of about 50-100us, some have a bivalent round
> trip of either around 150us but also around 300 us. Some have a
> wildly varying ( a few packets around the 150, most around 300us,
> with scatter up to 10ms.) round trip. It is a total mess. It really
> seems like the GB switches are a disaster for timing. Of course
> running them at 100 would not help. It is a problem with the switch
> design I believe.

Do you see the issue with classic 100Mbit/s NICs connected to your
gigabit switch?  Or do you only see the issues with 1 GbE connected
systems?  If so, then go ahead and disable the interrupt coalescing
and see what that changes.

Earlier I said that switches wouldn't coalesce - I should say
"traditional" (my use of terminology) switches wouldn't - if the
"switch" is really a Linux instance running bridging software then...

> I have no idea where this horror is taking place-- the NICs, the
> switches, ....

But you are sure it is gigabit the technology... :-)

rick jones
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