[Babel-users] us vs ns resolution in babel rtt branch

[Dave Taht]

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.
>
> Dave,
>
> 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
stuff.

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!

https://plus.google.com/u/0/107942175615993706558/posts/TVX3o84jjmb