[Babel-users] us vs ns resolution in babel rtt branch
dave.taht at gmail.com
Thu Apr 2 21:52:12 UTC 2015
I think my overall point regarding precision and granularity is that I
am thinking in terms of babel in high speed switch/routers at 100+GigE
and implemented in hardware, with timestamping even more accurate than
what even ptp can achieve.
but I will wait til babel 3.0. :)
On Thu, Mar 19, 2015 at 7:45 PM, Dave Taht <dave.taht at gmail.com> wrote:
> On Thu, Mar 19, 2015 at 2:36 PM, Juliusz Chroboczek
> <jch at pps.univ-paris-diderot.fr> wrote:
>>> I still kind of like getting down to ns resolution here. A single 64
>>> byte packet at 10gigE takes like 64ns.
>> As Baptiste mentioned, babeld measures latencies with a granularity of
>> 1盜, and a precision of a few hundred 盜. That means we have two to three
>> orders of magnitude to grow. We've already changed the protocol once to
>> reduce the granularity, at your prompting, and there's no point doing that
>> again until the precision becomes comparable to the granularity.
> I'll live with it as it is. Sorry for the noise. I note that I think
> you tried to type in us above, and it shows up as cute little houses
> on my mailer. :)
>> Dave, if you'd like this to happen, you'll want to produce experimental
>> data that show that the timestamps' granularity is an actual limitation.
> Well, I'd have to rope in some 10GigE users of babel to try it fully
> and produce patches that did what I wanted to autosense capacity and
> utilization. Those are still quite feasible, and I figure I could
> treat long term averages below 1us as a means of better sensing the
> higher bandwidths.
> I had done some measurements using other tools (isoburst and some
> kernel stuff) and got WAY better precision than you got. Jesper got
> even better, as noted on this thread earlier.
> So it would be best for me to finally sink the time into doing up high
> speed network RTT based routing metrics the way I envisioned them 1.5
> years ago, and perhaps I'll have time this summer to try that,
> piecemeal, whilst we test the upcoming deployment of all the other
> I am happy that 10GigE seems likely to become more common in the
> future, with dual 10GigE nics on the latest intel socs. I have
> delusions of connecting up rings of machines again without a central
> switch, but I guess it's saner to bridge them all together.
>> -- Juliusz
> Dave Täht
> Let's make wifi fast, less jittery and reliable again!
Let's make wifi fast, less jittery and reliable again!
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