On Wed, Oct 30, 2013 at 5:15 PM, Juliusz Chroboczek <[email protected]> wrote: > Baptiste: > >> - Babel sees a RTT that is 400 µs higher than ping6. The babel-rtt >> implementation timestamps outgoing message as late as possible, and >> timestamps incoming messages as early as possible, but it's not >> perfect. > > The good news, of course, is that the offset is pretty constant, so > the samples computed by babeld are good enough to be input to the > metric computation. The smoothed samples would appear to have > a precision of roughly 200us, which should be good enough for almost > any application.
I will try to get an equivalent measurement on vastly weaker hardware (ar71xx/ath9k) on my next set of builds (after ietf), ~2 weeks. I would like measurements under various loads... > Baptiste, I'm wondering if you can count the number of Ethernet > switches that way. In cut-through mode this switch claims 400ns or so latency. http://ark.intel.com/products/76302/Intel-Ethernet-Switch-FM5224 Older models of this were better - 300ns or less. > >> I'm delighted to see this measurement as collected by babel > > I knew you would be :-) > >> my sekret plan was to be able to measure heavy traffic benchmarks vs >> various qdiscs like the new "fq" and older fq_codel ones... > > Well, the reason we decided it's worthwile to improve the precision of > our measurements is that, according to Jim, you had a secret plan to > use RTT to measure link-layer congestion in Wifi meshes. Yes, ~200us precision is nicely less than a txop. This will help. > How many > more secret plans do you have? One or two. ;) > -- Juliusz > > _______________________________________________ > Babel-users mailing list > [email protected] > http://lists.alioth.debian.org/cgi-bin/mailman/listinfo/babel-users -- Dave Täht Fixing bufferbloat with cerowrt: http://www.teklibre.com/cerowrt/subscribe.html _______________________________________________ Babel-users mailing list [email protected] http://lists.alioth.debian.org/cgi-bin/mailman/listinfo/babel-users
