[Ecn-sane] ect(1) queue selector question

[Pete Heist]

Fwiw I captured a "Dave's wish list" file so we have it around. We do
come back to these lists sometimes.

There's not much here currently in our project plan except for more
testing on bursty mac layers, in the lab at first, as part of work that
should make it much easier to run more types of tests, and concurrently
so they get done faster. If HFCC has a deployment problem with bursty
traffic that can't be solved, it seems like something that needs to be
worked out asap. We made quite a utilization improvement by using Codel
to do SCE signaling, but what are the tradeoffs and how does that work
in different conditions? Worth trying to answer with testing.

On Mon, 2021-03-08 at 17:18 -0800, Dave Taht wrote:
> I am of course much happier interacting here than over on tsvwg.
> 
> I would like very much
> 
> A large scale bit twiddling test from the larger providers of
> fq_codel
> and cake based hw and middleboxes.
> 
> extensive testing on lte and wifi transports. even emulated.
> the sce patches polished up and submitted for review to netdev as
> what
> we call there, an RFC
> the ability to test both SCE and L4S on openwrt (backport thereof)
> 
> I know there's been a lot of work on other qdiscs than cake, but
> haven't paid much attention. netdev review would be nice.
> 
> A simple internet-wide test of say bittorrent, or using an adserver
> method like what apnic uses.
> 
> Most of all I'd really like someone to take a stab at RFC3168 support
> for BBR. And by that, I don't mean a reduction by half, but to
> institute an RTT probe phase. A fixed rate reduction per RTT is
> simply
> not
> going to work IMHO, period, on lte and wifi. I'm sure dave miller
> would accept such a patch, and this would also lead towards better
> ecn
> support across the internet in general... at least from the
> perspective of the one provider I have an in with, dropbox.
> 
> SCE support for BBRv2 would be nice also.
> 
> And I know, a pony, all sparkly and stuff. I find it very difficult
> to
> summon the cojones to do a drop of work in this area, and I keep
> cheering you on - especially on the bug fixing and wonderful scripts
> and data you've provided so far, and I do wish I could find some way
> to help that didn't cause so much ptsd in me.
> 
> I wish I merely knew more about how dctp was configured in the data
> center. So far as *I* know its on dedicated switches mostly. I would
> vastly prefer a dscp codepoint for this, also.
> 
> On Mon, Mar 8, 2021 at 4:36 PM Pete Heist <pete at heistp.net> wrote:
> > 
> > Sorry for reviving an old thread as I haven't been on this list in
> > a
> > while:
> > 
> > > > SCE proposes to use ect(1) as an indicator of some congestion
> > > > and
> > does
> > > > not explictly
> > > > require a dscp codepoint in a FQ'd implementation.
> > >       Pretty much. I do think that a demonstration using an
> > > additional DSCP to create a similar HOV lane for SCE would have
> > > gone
> > > miles in convincing people in the WG that L4S might really not be
> > > as
> > > swell as its proponents argue, IMHO it won the day more with its
> > > attractive promise of low latency for all instead of what it
> > delivers.
> > 
> > On that, I don't think any of us knows how things will end up or
> > how
> > long it will take to get there...
> > 
> > I do agree that the interim meeting leading up to the codepoint
> > decision could have gone better. Everything went great until it
> > came to
> > how to deploy SCE in a small number of queues. We had dismissed the
> > idea of using DSCP, because we thought it would be panned for its
> > poor
> > traversal over the Internet. That may still have been the case, but
> > it
> > also may have worked if sold right. We thought that AF alone might
> > be
> > enough to get past that part, but it wasn't.
> > 
> > We already implemented a two-queue design that uses DSCP, but
> > either
> > there wasn't much interest, or we didn't sell it enough. Plus, for
> > those who demand a two queue solution that requires no flow
> > awareness
> > at all, DSCP alone may not get you there, because you still need
> > some
> > reasonably fair way to schedule the two queues. So that might have
> > been
> > the next line of criticism. Scheduling in proportion to the number
> > of
> > flows each queue contains is one effective way to do that, but that
> > requires at least some concept of a flow. Perhaps there's another
> > way
> > that doesn't introduce too much RTT unfairness, but I'm not sure.
> > 
> > In our defense, there was already a lot of support built up for
> > L4S,
> > and stepping in front of that was like stepping in front of a
> > freight
> > train no matter what we did. I think we've made a decent argument
> > in
> > the most recent version of the SCE draft that ECN is a "network
> > feature" which carries higher risks than drop-based signaling, and
> > warrants the requirement for unresponsive flow mitigation, for
> > starters. That of course requires some level of flow awareness,
> > which
> > then makes various queueing designs possible. And, there may still
> > be
> > deployment possibilities with DSCP, as Rodney mentioned.
> > 
> > Anyway, there's progress being made on SCE, with some new ideas and
> > improvements to testing tools coming along.
> > 
> > Pete
> > 
> > 
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> 
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