Re: [aqm] floating a draft charter

[Luca MUSCARIELLO <[e-mail]>]

AFAIK, Chipcos for home gateways (Broadcom, Ikanos, Intel), network 
processors (Cavium),
but also Cisco, Juniper and Alcatel-Lucent make a difference between 
class based queuing and
dropping algorithms. The first is implemented everywhere in different 
ways and I do not think
there would be relevant work to do there (except for HTB in Linux which 
is really bad in terms
of performance, IMHO).

Dropping algorithms is used frequently as a term to describe AQM, e.g. 
in CLI based configuration
systems you may find (in commercial Linux based products) SFQ among the 
dropping algorithms.

It is clearly an abuse of language but common practice.  I unfortunately 
agree with Dave, and we discussed about
that in Paris, that chipcos do not take care about flow based queue 
management (typically withing a given class).
Only Linux  does that, but many products make use of Linux only for the 
slow path while the fast path is managed in hardware.

Deploying QoS (including de-bloating in QoS) based on Linux is soon 
broken by the trend to distribute packet processing
in dedicated processing units and  chipco ignore completely queue 
management there.
Anytime I ask whether the chip implements deficit round round robin the 
answer is "of course!" and in the
end it  turns out to be *modified* deficit round robin, i.e. class based 
queuing with up to say 64 queues.
Which is not what I am looking for.

One solution would be to move everything to software, but the cost of 
the chip that guarantees the same switching
throughput is much higher.

I would suggest to put more emphasis that something new is being 
proposed here adding
flow based packet scheduling as a novel item in the charter (in addition 
to class based, dropping or
congestion notification).  Using Smart Queue Management seems misleading 
to me or not enough.

Best regards,
Luca


-- 
France Telecom R&D - Orange Labs
MUSCARIELLO Luca - NMP/TRM
38 - 40, rue du General Leclerc
92794 Issy Les Moulineaux Cedex 9 - France
Tel : [phone]
http://perso.rd.francetelecom.fr/muscariello



On 06/05/2013 09:44 AM, Dave Taht wrote:
>
>
> On Wed, Jun 5, 2013 at 12:09 AM, Rong Pan (ropan) <[e-mail] 
> <mailto:[e-mail]>> wrote:
>
>     I understand packet scheduling is important. However, most network
>     devices today treat these two issues separately: classed-based
>     scheduling/queueing and drop/mark algorithms. In class-based
>     queueing, vendors differ in how many classes that they support: 2,
>     4 or 8. In drop/mark algorithm, vendors tend to implement both
>     tail-drop and WRED.
>
>
> I really have a great deal of trouble extrapolating to "vendors" here. 
> I suppose you mean "big iron vendors", like Juniper, or Allied 
> Telesis, which haven't weighed in on this list yet. In the CMTS market 
> there are three players, and while I know what Arris can do, I would 
> prefer an Arris representative to say. In terms of chipset makers 
> ethernet support, most don't don't support anything in hardware, 
> neither do the low end bridge chips, and thus they rely on software to 
> do either AQM or FQ, in addition to doing useful things like 
> firewalling or NAT. In servers, home routers, and handhelds, linux 
> based devices are prevailant and can easily do just about anything. (I 
> recently had a theorist badger me about doing a particle model for 
> scheduling packets, because the GPU is effectively free on many common 
> chipsets. I'm sooo not going there, but he is). Wifi chipsets 
> generally have no strategy other than 802.11e for managing queues. 
> Most of the France Telecom's dsl devices run shortest queue first, 
> with longest queue drop. The list goes on and on...
>
>
>
>     I think we can continue to treat these two issues separately as it
>     has been done in practice.
>
>  Scheduling and drop algorithms have long been used in combination in 
> practice. Examples include the venerable wondershaper, and openwrt's 
> QoS system, which for most of the last 7 years or so was HFSC + SFQ + 
> RED. Dozens of other examples exist, but not on the gear you are 
> familiar with.
>
>     We can prove the values of delay-based AQM and we can also prove
>     the value of FQ.
>
>
> Sure. Thing is, we've pretty much proven that the two in combination 
> are better than either, singly. Do you not agree with that assessment?
>
>     The goal of AQM is to give early congestion notification before
>     the buffer becomes full or the delay gets big.
>
>
> If you want to define AQM as Active Queue LENGTH management, then go 
> right ahead and try. Actually I was thinking hard about expanding the 
> scope of this proposed working group to be "Smart Queue Management" - 
> which neatly not only encompasses FQ and queue length management, but 
> also extends out to nagging problems like sanely rate limiting ipv6 
> ICMP responses to someone probing someone's entire /64 address space, 
> and dealing with other sorts of attack like that, and problems like 
> incast.
>
> Similarly, the problem of dealing with diffserv marking remains, as to 
> how (or if) it would correctly interact with a SQM system.
>
> Things like iptables don't seem to have a home within the ietf 
> presently (?)
>
>     Scheduling algorithms determine bandwidth allocation and weighted
>     fairness among different classes/flows. We don't have to mandate a
>     particular scheduling algorithm with a particular AQM scheme.
>
>
> Concur with that very much. I continue to experiment with QFQ+, DRR, 
> WFQ, SFQ, and other techniques.
>
>     Vendors shall be free to choose their best performance-cost
>     tradeoff point. I think it would be challenging to force vendors
>     to adopt a fixed set.
>
>
> Concur. Let the best set of ideas win both here and in the 
> marketplace! But an end goal should be some effective form of SQM *on 
> by default*, on everything.
>
>
>     Best Regards,
>
>     Rong
>
>
>
>     From: Jim Gettys <[e-mail] <mailto:[e-mail]>>
>     Date: Tuesday, June 4, 2013 8:47 AM
>     To: Wesley Eddy <[e-mail] <mailto:[e-mail]>>
>     Cc: Mirja Kuehlewind <[e-mail]
>     <mailto:[e-mail]>>, "[e-mail]
>     <mailto:[e-mail]>" <[e-mail] <mailto:[e-mail]>>
>
>     Subject: Re: [aqm] floating a draft charter
>
>     There are a number of things I want to see:
>
>     1) packet scheduling is as important as drop/mark algorithms: it
>     is the two together that is such a win with fq_codel.  So I, for
>     one, would be *very* unhappy to see a charter that meant it was
>     out of scope to discuss and document scheduling and flow queuing
>     strategies.  And packet scheduling can interact with drop mark
>     algorithms.
>
>     Optimal scheduling depends on where you are in the network (e.g. a
>     host, versus home router, vs. ISP head end, etc.); documenting
>     what makes the most sense where would likely help both
>     implementors of software and hardware and operators of those
>     networks.  I've given some thought to the area, but until we have
>     running code, it's hand waving, but probably won't be hand waving
>     in a year or two.
>
>     2) many mark/drop algorithms can co-exist (and generating
>     informational RFC's to help customers write RFP's is worth while):
>     but so far, there is no universal "one size fits all" mark/drop
>     algorithm that is optimally effective everywhere.  Kathy and Van
>     say a primary goal of CoDel was "first, do no harm", rather than
>     "optimal under all circumstances".  The goal was an algorithm that
>     never hurt you and would always be safe to have enabled. CoDel's
>     constants were chosen so that CoDel will work at the edge of the
>     network with planetary length paths in the face of highly variable
>     bandwidth.
>
>     But CoDel inside a datacenter (unless you mess with its constants)
>     is not effective in a timely fashion.
>
>     People have feared tuneable algorithms such as (W)RED can hurt
>     them, so what we have had for AQM is sometimes not present at all,
>     or not enabled (even in nodes that it would help greatly).  Note
>     that one of Dave Taht's discoveries was that RED had been broken
>     in the Linux source tree for 5 years and *no one had noticed*.
>
>     Maybe someday we'll reach nirvana with a drop/mark algorithm that
>     "just works" everywhere well all the time and can never hurt and
>     always works perfectly, but that's a lofty goal left for research;
>     in the meanwhile, helping people understand what to use where in
>     the network and the tradeoffs is important.
>
>     But if CoDel (as we believe) or some other algorithm really is
>     "first, do no harm" without tuning,  it has great value to be on
>     by default just to prevent the disaster an operator not enabling
>     any AQM at all; the world will never be worse than that, and
>     usually be radically better. Anything that *requires* tuning of
>     knobs to work is a not a candidate....
>
>     3) Some algorithms may be hard to retrofit into existing
>     platforms.  For example, if you can't timestamp a packet, it's
>     really hard to use CoDel, which is an algorithm easy to implement
>     from scratch, but could be really hard retrofit in an existing
>     hardware design. I don't want to discourage people doing things a
>     lot better than nothing as a stop-gap, but people need to
>     understand that it may be a second best solution.
>
>     Again, advice as to what/where algorithms may be applicable will
>     help designers and operators both.  We face a 5-10 year transition
>     here, even if we succeed this time.
>
>     4) There are "feagtures" or lack of features that today's hardware
>     does that can/does make life for software very hard. Changes could
>     make life much easier.
>
>     For example, today's hardware makes it hard to do true head drop
>     (which hardware assist could make trivial).  Some have noticed
>     that at low bandwidth we may adjust CoDel parameters to work
>     around the lack of head drop and unaccounted for time in the
>     driver's ring buffers (which CoDel needs), since Linux's qdisc's
>     can't see the time in the rings. So there are a set of
>     recommendations to hardware and OS designers that would help the
>     state of the network: this simple head drop feature, packet
>     pacing, making GSO/TSO less evil, and so on, war stories on all
>     the places we've been working on debloating Linux to guide other
>     OS developers, etc.
>
>     This is really the other side of queue management: try to
>     encourage traffic and systems that is less bursty and gentle to
>     the network, so the AQM/scheduling algorithms don't have to work
>     as hard.
>
>     Such things should go someplace in the IETF, and if not here,
>     where?  Doing nothing anywhere is what I want to avoid.
>
>     Best regards,
>         Jim
>
>
>
>     On Thu, May 30, 2013 at 12:13 PM, Wesley Eddy <[e-mail]
>     <mailto:[e-mail]>> wrote:
>
>         On 5/30/2013 8:20 AM, Mirja Kuehlewind wrote:
>         >
>         > But my point is, we should not only to standardize more and
>         more AQM
>         > mechanisms because that's a large research area which maybe
>         even should be
>         > homed in the IRTF, but we need to find actually deployment
>         strategies. Having
>         > a working group on AQM will already help to make people
>         aware of the topic
>         > and maybe think about using AQM. But only standardizing more
>         and more AQM
>         > queue, might end up in investing a lot of working that
>         no-one will ever use.
>
>
>         I suggest appending something like this to the charter:
>
>           Many AQM algorithms have been proposed in academic
>         literature, but
>           very few are widely implemented and deployed.  A goal of the
>         working
>           group is to produce recommendations that will actually be
>         used, and
>           algorithms that will actually be implemented, deployed in
>         equipment,
>           and enabled.  Towards these ends, the group actively encourages
>           participation from operators and implementers, and will
>         coordinate
>           with the IETF OPS area and other relevant parts of the IETF and
>           Internet community.  Wider research and evaluation of AQM
>         mechanisms
>           shall be coordinated with the IRTF/ICCRG, and significant
>           participation in this WG from the academic and research
>         community is
>           highly desirable, when it is directly relevant to
>         implementation and
>           deployment.
>
>
>         We will definitely need to get engagement from some of the
>         operators
>         that participate in the IETF, and should solicit participation
>         more
>         widely outside as well (e.g. advertise to NANOG list, bufferbloat
>         list, etc.) in order to attract operators and implementers
>         that aren't
>         already aware of this activity.
>
>         Would this help to address your concern?
>
>
>         --
>         Wes Eddy
>         MTI Systems
>         _______________________________________________
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>
>
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>
>
>
> -- 
> Dave Täht
>
> Fixing bufferbloat with cerowrt: 
> http://www.teklibre.com/cerowrt/subscribe.html
>
>
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