[Cerowrt-devel] Anything but "AQM"

Dave Taht dave.taht at gmail.com
Fri Dec 20 16:58:45 EST 2013

On Fri, Dec 20, 2013 at 1:22 PM,  <dpreed at reed.com> wrote:
> Given that there is no likelihood of making localized queue management
> "intelligent" because it has no global information whatsoever, I strongly
> suggest that "smart" "intelligent" and even "active" are hugely misleading.
> They are based on a completely false premise - that queues should be allowed
> to build at all, and that local information can solve highly transient
> global problems.

David, I think we should have this discussion offline. I thought you were paying
attention on the bloat list.

> "Dumb Queue Management" is going to be far superior.  Keep the queue at zero
> length, and try to be fair.


> There's a simple way to do the latter - use a filter (similar to a Bloom
> filter) that captures recent/frequent users of the queue, and when the queue

Tried SFB. It didn't work.

> on an outbound link grows more than about 2-3 packets (double buffering is
> all you need to keep the link full) discard the most recent and frequent
> packets (or send information that tells them to slow down).

Nope, due to the bursty nature of tcp and of things like wifi packet
aggregation you need be able to absorbe a burst of an RTT's worth of
queue around, what kathy and van call "good queue".

I have a lot of hope that now that we are seeing "paced" tcp
schedulers that we'll see much less structure at the bottlenecks from
isochronous sources, but the batchy ones like gpon, wifi, and cable,
will induce more, and structure does seem to arrive from navigating
bottlenecks also, as per slide 30 in this:

> There's been a lot of wasted time and effort trying to build queues long
> enough so that you can be "intelligent", but by then you have already lost
> the battle.  You've gotten into a positive feedback loop where you have
> encouraged the endpoints to send more packets than you can ever drain out of
> the queue.

The goal here is 100% utilization at 0 latency. We are getting
preciously close to it with fq_codel and derivatives.

> I truly, truly do not understand why people don't look at realistic network
> loads and structures.

I like to think I do.

> On Friday, December 20, 2013 3:52pm, "Rich Brown" <richb.hanover at gmail.com>
> said:
>> Dave,
>> You wrote:
>> > What's in a name? AQM has been pretty thoroughly defined to equal
>> > active queue *length* management and not packet scheduling.
>> > Overloading "AQM" what cerowrt does is apt to cause even more
>> > confusion in the field than it already does. We discussed using LBO as
>> > a word but that appears hopelessly overloaded with leveraged buy out.
>> >
>> > I go back to one I liked a while back:
>> >
>> > Smart Queue Management. (SQM)
>> >
>> > This got dissed on the aqm list too, but so far a viable alternative
>> > TLA has not appeared. It's sufficiently different to hang a different
>> > definition off of ("Smart queue management is an intelligent
>> > combination of better packet scheduling (flow queuing) techniques
>> > along with with active queue length management (aqm)”)
>> and
>> > Any ideas for a name for packet scheduling, prioritization, and active
>> > queue management better than just "AQM", or "QoS"?
>> >
>> > SQM "Smarter Queue Management"
>> > CeroShaper
>> > LBO Latency and Bandwidth Optimisation
>> I was prepared to agree with “SQM”, and had written a long note
>> (below) when my brain uttered “Intelligent Queue Management”.
>> I’m not convinced that one is better than the other…
>> Rich
>> ===== The benefits of SQM ======
>> Wikipedia sez… SQM may refer to:
>> - Sociedad Química y Minera de Chile - a Chilean mining and chemical
>> enterprise
>> - Software quality management
>> - Spectrum quality management
>> - Supplier Quality Management
>> - Sensors Quality Management Inc. - provides unbiased evaluations of a
>> company's
>> operations relating to issues of quality, service, cleanliness and value
>> - Sky Quality Meter, a device for measuring light pollution
>> and also : São Miguel do Araguaia airport IATA code
>> sqm may refer to :
>> - square metre
>> - Windows Live Messenger log file extension
>> So it doesn’t appear that there are any seriously conflicting uses of that
>> TLA…
>> And I prefer “Smart Queue Management” to “Smarter Queue
>> Management”. We’ll leave to someone else to go out on the weak branch
>> and espouse “Smarter queue management” and “Smartest queue
>> management”. (What comes after that? “Smart and a half”,
>> Smart**2"?)
>> Rich
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Dave Täht

Fixing bufferbloat with cerowrt: http://www.teklibre.com/cerowrt/subscribe.html

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