Re: [Cerowrt-devel] High Performance (SSH) Data Transfers using fq_codel?

["David P. Reed" <dpreed@reed.com>]

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Filling intermediate buffers doesn't make the tcp congestion algorithms work.  They just kick in when the buffers are full! And then you end up with a pile of packets that will be duplicated which amplifies the pressure on buffers!

If there could be no buffering,the big file transfers would home in on the available capacity more quickly and waste fewer retransmit - while being friendly to folks sharing the bottleneck!

The HPC guys really don't understand a thing about control theory...

On Nov 13, 2014, Aaron Wood <woody77@gmail.com> wrote:
>I have a couple friends in that crowd, and they _also_ aren't using
>shared
>lines.  So they don't worry in the slightest about congestion when
>they're
>trying to keep dedicated links fully saturated.  They're big issue with
>dropped packets is that some of the TCP congestion-control algorithms
>kick
>in on a single dropped packet:
>http://fasterdata.es.net/network-tuning/tcp-issues-explained/packet-loss/
>
>I'm thinking that some forward-error-correction would make their lives
>much, much better.
>
>-Aaron
>
>On Thu, Nov 13, 2014 at 7:11 PM, Dave Taht <dave.taht@gmail.com> wrote:
>
>> One thing the HPC crowd has missed is that in their quest for big
>> buffers for contenental distances, they hurt themselves on shorter
>> ones...
>>
>> ... and also that big buffers with FQ on them works just fine in the
>> general case.
>>
>> As always I recomend benchmarking - do a rrul test between the two
>> points, for example, with their recomendations.
>>
>>
>> On Fri, Oct 17, 2014 at 4:21 PM, Frank Horowitz <frank@horow.net>
>wrote:
>> > G’Day folks,
>> >
>> > Long time lurker. I’ve been using Cero for my home router for quite
>a
>> while now, with reasonable results (modulo bloody OSX wifi stuffola).
>> >
>> > I’m running into issues doing zfs send/receive over ssh across a
>> (mostly) internet2 backbone between Cornell (where I work) and West
>> Virginia University (where we have a collaborator on a DOE sponsored
>> project. Both ends are linux machines running fq_codel configured
>like so:
>> >         tc qdisc
>> >         qdisc fq_codel 0: dev eth0 root refcnt 2 limit 10240p flows
>1024
>> quantum 1514 target 5.0ms interval 100.0ms ecn
>> >
>> > I stumbled across hpn-ssh <https://www.psc.edu/index.php/hpn-ssh>
>and
>> —  of particular interest to this group — their page on tuning TCP
>> parameters:
>> >
>> > <http://www.psc.edu/index.php/networking/641-tcp-tune>
>> >
>> > N.B. their advice to increase buffer size…
>> >
>> > I’m curious, what part (if any) of that advice survives with
>fq_codel
>> running on both ends?
>> >
>> > Any advice from the experts here would be gratefully received!
>> >
>> > (And thanks for all of your collective and individual efforts!)
>> >
>> > Cheers,
>> >         Frank Horowitz
>> >
>> >
>> > _______________________________________________
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>> > Cerowrt-devel@lists.bufferbloat.net
>> > https://lists.bufferbloat.net/listinfo/cerowrt-devel
>> >
>>
>>
>>
>> --
>> Dave Täht
>>
>> thttp://www.bufferbloat.net/projects/bloat/wiki/Upcoming_Talks
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>>
>
>
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-- Sent from my Android device with K-@ Mail. Please excuse my brevity.

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