[Codel] [RFCv2 PATCH] iproute2: Add ecn_target option to codel and fq_codel

Dave Taht dave.taht at gmail.com
Mon Jun 25 10:54:53 EDT 2012

On Sun, Jun 24, 2012 at 10:29 PM, Eric Dumazet <eric.dumazet at gmail.com> wrote:
> On Sun, 2012-06-24 at 22:00 -0700, Dave Täht wrote:
>> From: Dave Taht <dave.taht at bufferbloat.net>
>> ECN was not part of the original codel design and adding support
>> for it revealed problems in two areas. 1) ECN can be gamed.
>> 2) Dropping packets under overload more rapidly frees up
>> bandwidth than marking packets.
>> Two possible scenarios of use - on egress from a network,
>> ecn_target could be set low, to drop more often, to
>> ensure lowest latency for other packets.
>> On ingress, it could be set high to mark packets more often,
>> to lower data loss while still signalling the end application
>> that bandwidth is a problem.
>> ecn_target is not engaged until after codel enters a dropping
>> state overall.
> I would suggest 'drop_above' instead of ecn_target, since its quite
> different than the 'target'

OK. I will respin this after resolving the issue I raised in the previous patch
comment (just switch ecn to being an int?), and do some testing. As noted
I was (de)impressed at the amount of ecn drops I had with it set to 2*target
on pure ecn enabled streams. In one test it was 95% drops...

And I'm still open to saner approaches. Another one might be to at graduated
levels drop big packets down to smaller ones.

> (And dont display/output it if ecn is not set, no need to confuse users
> who didn't enable ecn on CoDel)
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Dave Täht
http://www.bufferbloat.net/projects/cerowrt/wiki - "3.3.8-6 is out
with fq_codel!"

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