[Codel] [Make-wifi-fast] fq_codel_drop vs a udp flood

Eric Dumazet eric.dumazet at gmail.com
Mon May 2 11:01:42 EDT 2016

On Mon, 2016-05-02 at 16:47 +0300, Roman Yeryomin wrote:

> So it looks to me that fq_codel is just broken if it needs half of my resources.


When I wrote fq_codel, I was not expecting that one UDP socket could
fill fq_codel with packets, since we have standard backpressure.

SO_SNDBUF default on UDP does not allow to send more than 256 packets in
a qdisc. So when sk_sndbuf limit is hit, sendmsg() either blocks or
returns an error (if in non blocking mode)

So it looks like someone really tries hard ;)

To reproduce the issue I had to change (as root user)

echo 1000000 >/proc/sys/net/core/wmem_default

_and_ setup fq_codel with a much lower limit than the default 10240

tc qdisc replace dev eth0 root fq_codel limit 300

So please try this fix :


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