[Bloat] [aqm] TSO sizing fixes and the new paced "fq" scheduler in Linux 3.12

Eric Dumazet eric.dumazet at gmail.com
Wed Sep 25 11:15:52 EDT 2013

On Tue, 2013-09-24 at 14:25 +0200, James Roberts wrote:
> No one responded to Luca's Sept 1 comment (on the bloat list) that the
> new code seems to do tail drop rather than longest queue drop. 
> If this is so, bandwidth sharing will not be fair since FQ alone is
> not enough. This was shown in the previously cited Bell Labs
> paper : http://ect.bell-labs.com/who/stiliadi/papers/jsac99.pdf. The
> following table is copied from the paper.

This paper assumes TCP stack can push cwin packets in the queue.
We no longer have this behavior with linux.

If you have drops on FQ, then you have a serious problem with your

FQ is meant to be used on hosts, not on routers.

For routers, fq_codel is fine.

TCP Small Queues limits the number of packets in Qdisc for any tcp flow
(2 packets). Default FQ setting allows 10000 packets.

You can add tail drop on FQ if you really want, but I never had a single
drop in my FQ settings, on 20Gbps links and thousands of flows.

Therefore I did not add complexity to solve a non problem.

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