Re: [Codel] R: Jumbo frames with fq_codel

[Dave Taht <dave.taht@gmail.com>]

On Mon, Nov 25, 2013 at 10:17 AM, Alessandro Bolletta
<alessandro@mediaspot.net> wrote:
>>On Mon, Nov 25, 2013 at 10:02 AM, Alessandro Bolletta <alessandro@mediaspot.net> wrote:
>> Hi guys,
>> I'm working on an environment which runs on jumbo ethernet frames (about 1550bytes) and I would ask you if do you think that it's needed >a trick in order to correctly debloat interfaces as ath9k and ag71xx which carries such big frames.
>
>>I am under the impression that the ag71xx does not support jumbo frames.
>>Slightly larger than usual frames? dunno.
>
> We are thinking to implement jumbo frames support on some devices based on ag71xx :)
> Many SoCs support up to 2028 bytes or 4076 bytes of MTU but the driver still can't manage MTUs higher than 1518bytes.
>
>>the ath9k supports frames up to the size of the wireless standards (23xx bytes or so)
>
> Yes.
>
>>fq_codel's internal quantum is the actual ip packet size, not the wire size.
>>at lower bandwidths it pays to have a lower quantum (like 300) on outgoing interfaces.
>
>>In openwrt the default on all interfaces is 300, which I dont necessarily agree with.
>
> Ok. I thought that codel would leverage on layer-2 parameters, as the size of the ethernet frame.

One of the beauties of codel is it doesn't care the size of the frame
at all, it only cares about how long it takes to deliver it.

Now, there are some interesting interactions between codel delivering
a big fat TSO string of packets and then a smaller packet (collatoral
damage), but they aren't bad, and there's fixes in 3.12 for tso that
make life saner.

fq_codel's quantum controls the degree of mixing between flows, set it
really low (say 300) to help voip and acks out on slow asymmetric
links, don't set it lower, otherwise leave it alone.

>>
>> Thanks
>>
>> --
>> Alessandro Bolletta
>> Mediaspot S.r.l.
>>
>>
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>
>
>
> --
> Dave Täht
>
> Fixing bufferbloat with cerowrt: http://www.teklibre.com/cerowrt/subscribe.html
>
>
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-- 
Dave Täht

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