On Tue, Jul 24, 2018 at 2:39 PM Benjamin Cronce <[email protected]> wrote: > > > > On Tue, Jul 24, 2018 at 3:57 PM Dave Taht <[email protected]> wrote: >> >> On Tue, Jul 24, 2018 at 1:11 PM Benjamin Cronce <[email protected]> wrote: >> > >> > Maybe the Bobbie idea already would do this, but I did not see it >> > explicitly mentioned on its wiki. >> >> you are basically correct below. bobbie's core idea was a kinder, >> gentler, deficit mode policer, with something fq_codel-like aimed at >> reducing accumulated bytes to below the set rate. >> >> this is way different from conventional policers >> >> > The below is all about shaping ingress, not egress. >> > >> > My issue is that my ISP already does a good job with their AQM but nothing >> > is perfect and their implementation of rate limiting has a kind of burst >> > at the start. According to speedtests, my 250Mb connection starts off >> > around 500Mb/s and slowly drops over the next few seconds until a near >> > perfect 250Mb/s steady state. >> >> ideally their htb shaper would use fq_codel as the underlying qdisc. >> Or at least reduce their burst size to something saner. I hope it's >> not a policer. >> >> You can usually "see" a policer in action. Long strings of packets are >> dropped in a row. > > > I feel as if this new configuration is not quite a policer as it feels much > less abrupt as the old configuration. It used to have massive loss spikes > that wrecked havoc on other flows and make the fat TCP flows have a kind of > rebound. Their newer setup seems to be gentler. While there is an increased > rate of loss as it attempt to "slowly" settle at the provisioned rate, it's > not like the cliff it used to be, it actually has a slope.
well, ask 'em. >> >> >> > The burst at the beginning adds a certain amount of destabilization to the >> > TCP flows since the window quickly grows to 500Mb and then has to backdown >> > by dropping. If I add my own traffic shaping and AQM, I can reduce the >> > reported TCP retransmissions from ~3% to ~0.1%. >> >> sure. >> >> >> >> >> > >> > The problem that I'm getting is by adding my own shaping, a measurable >> > amount of the benefit of their AQM is lost. While I am limited to Codel, >> > HFSC+Codel, or FairQ+Codel for now, I am actually doing a worse job of >> > anti-bufferbloat than my ISP is. Fewer latency spices according to >> > DSLReports. >> >> ? measured how. > > Just looking visual at the DSLReport graphs, I more normally see maybe a few > 40ms-150ms ping spikes, while my own attempts to shape can get me several > 300ms spikes. I would really need a lot more samples and actually run the > numbers on them, but just causally looking at them, I get the sense that mine > is worse. too gentle we are perhaps. out of cpu you may be. >> >> >> > >> > This also does not touch on that the act of adding back-pressure in its >> > nature increases latency. I cannot say if it's a fundamental requirement >> > in order to better my current situation, but I am curious if there's a >> > better way. A thought that came to me is that like Bobbie, do a light >> > touch as the packets have already made their way and you don't want to >> > aggressively drop packets, but at the same time, I want the packets that >> > already made the journey to mostly unhindered enter my network. >> > >> > That's when I thought of a backpressure-less AQM. >> >> I like the restating of what policers do.... > > I think I need to look at the definition of a policer. I always through them > as a strict cut-off. I'm not talking about mass dropping packets beyond a > rate, just doing something like Codel where a packet here and there get > dropped at an increasing rate until the observed rate normalizes. bobs below the set rate long enough to drain the queue upstream. >> >> >> >Instead of having backpressure and measuring sojourn time as a function of >> >how long it takes packets to get scheduled, predict an estimated sojourn >> >time based on the observed rate of flow, but allow packets to immediately >> >vacate the queue. The AQM would either mark ECN or drop the packet, but >> >never delay the packet. >> >> aqms don't delay packets. shapers do. > > My described "AQM" is not a shaper in that it does not schedule > packets(possibly FIFO and at line rate), but does understand bandwidth. It > neither delays packets nor has a strict cut-off. It essentially would allow > packets to flow through at line rate, but if the "average" rate gets too > high, it may decide to drop/mark the next packet. It might be described as > bufferless shaping where the goal is to minimize packet-loss. Shaping purely > by a gentle rate of increasing loss. sure. > > Of course this whole thought may be total rubbish, but I figured I'd throw it > out there. not rubbish, could be better than policing. >> >> >> > In summary, my ISP seems to have better latency with their AQM, but due to >> > their shaper, loss during the burst is much higher than desirable. >> > >> > Maybe this will be mostly moot once I get fq_codel going on pfSense, but I >> > do find it an interesting issue. >> >> I thought it's been in there for a while? > > Technically, but not practically. It should be easily available via the UI > with 2.4.4 which is slowly nearing release. >> >> >> > _______________________________________________ >> > Bloat mailing list >> > [email protected] >> > https://lists.bufferbloat.net/listinfo/bloat >> >> >> >> -- >> >> Dave Täht >> CEO, TekLibre, LLC >> http://www.teklibre.com >> Tel: 1-669-226-2619 -- Dave Täht CEO, TekLibre, LLC http://www.teklibre.com Tel: 1-669-226-2619 _______________________________________________ Bloat mailing list [email protected] https://lists.bufferbloat.net/listinfo/bloat
