Re: [Bloat] Graph of bloat

[Jan Ceuleers <jan.ceuleers@gmail.com>]

On 08/07/15 18:11, Jan Ceuleers wrote:
> On 08/07/15 17:55, Dave Taht wrote:
>> That is a very interesting graph! Does ntp adjust system time backward
>> based on getting nearly all it's samples with well over a 1/2 second
>> of induced delay?
> 
> If there is a consistent asymmetrical delay then yes.

Let me qualify that "yes".

Normally ntpd will ensure that the system time as observed by the kernel
and applications always increases monotonically. The exception is where
the system time differs too much from what ntpd considers to be the
correct time and where ntpd is given permission to step the time (e.g.
using the -g command-line switch). In this case ntpd can step backwards.

What I meant in my previous message is that ntpd's idea of true time is
arrived at based on the assumption that the network delay is the same in
both directions to its servers. So if there is a systematically
different delay in one direction relative to the other then this
assumption falls down and ntpd's assessment of true time will be skewed.

The huff-n-puff filter helps in cases where the asymmetry in the delay
is not systematic, e.g. where the upstream channel does not suffer from
bufferbloat.

Jan