[Codel] fq_codel_drop vs a udp flood

Eric Dumazet eric.dumazet at gmail.com
Tue May 3 09:35:31 EDT 2016

On Tue, 2016-05-03 at 12:50 +0000, Agarwal, Anil wrote:
> I should be more precise about the statement about the inaccuracy of the algorithm.
> Given that we dequeue packets in round robin manner, the maxqidx value may, on occasions, point to a queue 
> which is smaller than the largest queue by up to one MTU.

That is not true.

Linux qdiscs (fq_codel being one of them) can carry big packets, up to
64KB in size.

You can not assume GRO/GSO are disabled. We absolutely want them for
high performance.

There is no way fq_codel will track in real time the biggest flow 'just
in case we have to drop packets at enqueue()'

This is a conscious choice I made years ago.

This patch will fix the performance issue and keep the normal operations


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