Re: [Ecn-sane] FQ in the core

[Sebastian Moeller <moeller0@gmx.de>]

Hi Dave,



> On Mar 25, 2019, at 08:54, Dave Taht <dave.taht@gmail.com> wrote:
> 
> I don't really have time to debate this today.

	By all means put this on the back-burner until tomorrow....


> 
> Since you forked this conversation back to FQ I need to state a few things.
> 
> 1) SCE is (we think) compatible with existing single queue AQMs. CE
> should not be exerted in this case, just drop. Note that this is also
> what L4S wants to do with the "normal" queue (I refuse to call it
> classic).

	Call it the internet-queue then?

> 
> 2) SCE is optional. A transport that has a more agressive behavior,
> like dctcp, should fall back to being tcp-friendly if it
> sees no SCE marks and only CE or drop.

	And this is where LLLLS faces challenges as it needs to use heuristics to throttle back to tcp-friendliness, which wil also be intersting once LLLLS will start to try to follow BBR in potentially ignoring dropped packets...

> 
> 3) At 100Gbit speeds some form of multi-queue oft seems needed. (and
> this is in part why folk want to relax ordering requirements). So some
> form of multiple queuing is generally the case. At the higher speeds,
> DC's usually overprovision anyway.

	Okay, that should allow to calculate a proposal for a minimum re-ordering window? Because I believe that RACK should allow for a minimum re-ordering window to actually allow transit ARQ to work efficiently without needing many stalls.


> 4) The biggest cpu overhead for any of this stuff is per-tenant (in
> the dc) or per customer shaping. This benefits a lot from a hardware
> assist. (see senic). I've done quite a bit of DC work in the past 2
> years (rather than home routers), and have had a hard look at the
> underlying substrates for a few multi-tenant implementations....

	Can you actually talk about this?

> 
> 4) "dualq" hasn't tried to address the fact that most 10Gbit and
> higher cards have 8 or more hardware queues in the first place.
> 
> 5) Companies like preseem are shipping transparent bridges that do
> fq_codel/cake on customer traffic.
> 
> I've long been in periodic negotions with makers of "big iron" like,
> for example, the new 128 core huwei box and others I cannot talk about
> at the moment, to get so far as an existence proof.
> 
> So I'd like to kill the meme that SCE requires FQ, at least, for now,
> until after we do more tests.

	My point here is not that fq is required, but rather that single queue AQMs seem easier to abuse as they assume full cooperation by all participating flows.


> 
> As for FQ everywhere, well, I'd like that, but it's not needed in
> devices that already have sufficient multiplexing.

	That would be aggregation networks and transit/peering points, no? That still leaves the edge...


Again, please ignore until the IETF meeting is over.

Best Regards
	Sebastian


> 
> 
> 
> 
> 
> On Mon, Mar 25, 2019 at 8:16 AM Mikael Abrahamsson <swmike@swm.pp.se> wrote:
>> 
>> On Sun, 24 Mar 2019, Sebastian Moeller wrote:
>> 
>>> From my layman's perspective this is the the killer argument against the
>>> dualQ approach and for fair-queueing, IMHO only fq will be able to
>> 
>> Do people on this email list think we're trying to trick you when we're
>> saying that FQ won't be available anytime soon on a lot of platforms that
>> need this kind of AQM?
>> 
>> Since there is always demand for implementations, can we get an ASIC/NPU
>> implementation of FQ_CODEL done by someone who claims it's no problem?
>> 
>> Personally I believe we need both. FQ is obviously superior to anything
>> else most of the time, but FQ is not making itself into the kind of
>> devices it needs to get into for the bufferbloat situation to improve, so
>> now what?
>> 
>> Claiming to have a superior solution that is too expensive to go into
>> relevant devices, is that proposal still relevant as an alternative to a
>> different solution that actually is making itself into silicon?
>> 
>> Again, FQ superior, but what what good is it if it's not being used?
>> 
>> We need to have this discussion and come up with a joint understanding of
>> the world, otherwise we're never going to get anywhere.
>> 
>> --
>> Mikael Abrahamsson    email: swmike@swm.pp.se
>> _______________________________________________
>> Ecn-sane mailing list
>> Ecn-sane@lists.bufferbloat.net
>> https://lists.bufferbloat.net/listinfo/ecn-sane
> 
> 
> 
> -- 
> 
> Dave Täht
> CTO, TekLibre, LLC
> http://www.teklibre.com
> Tel: 1-831-205-9740