[Codel] fq_codel_drop vs a udp flood

Ben Greear greearb at candelatech.com
Sun May 1 01:08:17 EDT 2016

On 04/30/2016 08:41 PM, Dave Taht wrote:
> There were a few things on this thread that went by, and I wasn't on
> the ath10k list
> (https://www.mail-archive.com/ath10k@lists.infradead.org/msg04461.html)
> first up, udp flood...
>>>> From: ath10k <ath10k-boun... at lists.infradead.org> on behalf of Roman
>>>> Yeryomin <leroi.li... at gmail.com>
>>>> Sent: Friday, April 8, 2016 8:14 PM
>>>> To: ath10k at lists.infradead.org
>>>> Subject: ath10k performance, master branch from 20160407
>>>> Hello!
>>>> I've seen performance patches were commited so I've decided to give it
>>>> a try (using 4.1 kernel and backports).
>>>> The results are quite disappointing: TCP download (client pov) dropped
>>>> from 750Mbps to ~550 and UDP shows completely weird behavour - if
>>>> generating 900Mbps it gives 30Mbps max, if generating 300Mbps it gives
>>>> 250Mbps, before (latest official backports release from January) I was
>>>> able to get 900Mbps.
>>>> Hardware is basically ap152 + qca988x 3x3.
>>>> When running perf top I see that fq_codel_drop eats a lot of cpu.
>>>> Here is the output when running iperf3 UDP test:
>>>>      45.78%  [kernel]       [k] fq_codel_drop
>>>>       3.05%  [kernel]       [k] ag71xx_poll
>>>>       2.18%  [kernel]       [k] skb_release_data
>>>>       2.01%  [kernel]       [k] r4k_dma_cache_inv
> The udp flood behavior is not "weird".  The test is wrong. It is so filling
> the local queue as to dramatically exceed the bandwidth on the link.

It would be nice if you could provide backpressure so that you could
simply select on the udp socket and use that to know when you can send
more frames??

Any idea how that works with codel?


Ben Greear <greearb at candelatech.com>
Candela Technologies Inc  http://www.candelatech.com

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