[Codel] fq_codel_drop vs a udp flood

Roman Yeryomin leroi.lists at gmail.com
Thu May 5 07:32:34 PDT 2016

On 2 May 2016 at 20:08, Dave Taht <dave.taht at gmail.com> wrote:
> 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:
> http://blog.cerowrt.org/post/fq_codel_on_ath10k/
> 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.

commit hashes wouldn't help much, I was reverting patches (see
previous emails in this thread).

>> 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!
> http://blog.cerowrt.org

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