[Codel] fq_codel_drop vs a udp flood

Dave Taht dave.taht at gmail.com
Mon May 2 13:08:09 EDT 2016

On Mon, May 2, 2016 at 9:14 AM, Eric Dumazet <eric.dumazet at gmail.com> wrote:
> On Mon, 2016-05-02 at 18:43 +0300, Roman Yeryomin wrote:
>> On 2 May 2016 at 18:07, Eric Dumazet <eric.dumazet at gmail.com> wrote:
>> > On Mon, 2016-05-02 at 17:18 +0300, Roman Yeryomin wrote:
>> >
>> >> Imagine you are a video operator, have MacBook Pro, gigabit LAN and
>> >> NAS on ethernet side. You would want to get maximum speed. And
>> >> fq_codel just dropped it down to 550Mbps for TCP (instead of 750Mbps)
>> >> and to 30Mbps for UDP (instead of 900Mbps).
>> >> So, again, it looks broken to me.

The big regression trying to be addressed here is the decades long
increase in wifi overbuffering for slow and normal clients.

The number that was making me happy was seeing low speed clients
finally have sane behavior:

I will add your iperf flood test to the testbench. Certainly we don't
want to hurt peak speeds overmuch... but we'd also like to see people
trying traffic at lower speeds.

Incidentally if you are doing openwrt builds that would be of great help.

>> > Can you show us your qdisc config ?
>> Which build do you want? Before it broke or after?

Commit hashes for each would help.

> I want to check your qdisc configuration, the one that you used and
> where you had fq_codel performance issues
> tc -s -d qdisc

Not sure it's the qdisc version under test here. ? If it is, I'd be
perversely happy as for the first time ever the wifi layer started
exerting some backpressure on the upper layers of the stack.

I'm not sure which parts of which patchset are under test here,
either. I saw a few too many patches go by all around, and I am only
just this week able to add ath10k to my test matrix. Commit?

https://github.com/kazikcz/linux/commits/fqmac-v3.5 has a version of
fq_codel in it (and the underlying driver changes) *at the mac80211
layer*, not the qdisc layer. It disables the overlying qdisc. It will
need the equivalent new fq_codel_drop logic added to it, that eric
just added, also, to do better on the udp flood test.

There was a prior branch that did pretty darn well at high speeds,
results I put on that blog post I linked to above - 820Mbps for tcp,
an actual improvement on the baseline test. The current branch is
simpler and did not do as well due in part to not being integrated
with rate control (I think).

There are pieces dropping in all over, there was a amdsu patch,
another patch on rx/tx,

Dave Täht
Let's go make home routers and wifi faster! With better software!

More information about the Codel mailing list