Re: [Codel] R: Making tests on Tp-link router powered by Openwrt svn

[Dave Taht <dave.taht@gmail.com>]

On Fri, Dec 21, 2012 at 5:19 AM, Alessandro Bolletta
<alessandro@mediaspot.net> wrote:
> Hi jonathan,
>
>
>
> This is how i configured the testbed:
>
>
>
> I have a windows 8 laptop connected directly on the tplink/openwrt router.
> Tplink is also connected to a gigabit switch.
>
> So, i thought to make some file uploads from a linux samba file server
> connected to the switch to my windows 8 laptop, through SMB protocol (which
> uses TCP).
>
>
>
> In order to create the bottleneck, tplink router has two 10/100mbits ports.
> So, i restricted the port connected to the switch to 10Mbit half duplex.

Full duplex is the only thing we've ever tested.

Secondly what you are doing here is moving the buffering into the switch.

If you want to rate limit, use HTB. Either the simple_qos.sh or
qos-scripts can be used for this.

http://www.bufferbloat.net/projects/codel/wiki/Best_practices_for_benchmarking_Codel_and_FQ_Codel

> Also, i tried to decrease interval and target options in order to obtain a
> latency, for connections estabilished while upload is flowing, lower that 5
> ms.
>
> So i set target at 2ms and interval to 5ms.

You are misunderstanding target and interval. These control the
algorithm for determining when to drop. interval is set to 100ms by
default as to try to find a good estimate for the RTT, and target to
5ms as to have a goal for a maximum delay to aim for. These values
work well down to about 4Mbits, at which point we have been bumping
target up in relation to how long it takes to deliver a packet. A
value I've been using for target at 1Mbit has been 20, as it takes
13ms to deliver a large packet.

The way interval works is that once you've been consistently over the
target delay for the interval, the codel drop scheduler starts and you
drop a packet. If you are still over the delay for the interval/2,
drop another packet, if you are still over the delay for the next
interval/3 drop another packet. when you hit an ideal drop rate, stop
decreasing the interval.

Thank you for giving me a new thing to add to the above url.

>
> So this is the schema:
>
>
>
> laptop----tplink---switch---linuxserver
>
>
>
> where tplink is routing subnets.
>
>
>
> If i ping “linux server” i get very high latencies…and if i ping other PCs
> connected to the switch, i get about 10ms latencies.
>
>
>
> I also tried to lower target at 1 ms and interval at 2ms, but i see the same
> effects.
>
>
>
> If i disable fq_codel, i get always the same result.

you've moved the buffering into the switch. don't do that.

>
>
>
> Can you explain me where i’m going wrong?
>
>
>
> Thanks
>
>
>
> Da: Jonathan Morton [mailto:chromatix99@gmail.com]
> Inviato: giovedì 20 dicembre 2012 19.08
> A: Alessandro Bolletta
> Cc: Codel@lists.bufferbloat.net
> Oggetto: Re: [Codel] Making tests on Tp-link router powered by Openwrt svn
>
>
>
> Is the bottleneck actually at your router, or (as is more usual) at the
> modem?
>
> - Jonathan Morton
>
> On Dec 20, 2012 7:57 PM, "Alessandro Bolletta" <alessandro@mediaspot.net>
> wrote:
>
> Hi everybody,
> Today i made some tests on my tplink home router powered by the lastest
> snapshot build of Openwrt.
> So, i configured tc to make fq_codel the default queuing algorithm for 2 eth
> ports available on the router (leaving unchanged default values).
> So, i started some TCP sessions through my Windows client and I loaded the
> available bandwidth...but the test wasn't going as expected because i
> experienced packet loss and high delays as i did when the default simple
> fifo queue was the default queue.
> Is there something that i'm not understanding?
>
> Thanks,
> Alessandro Bolletta
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-- 
Dave Täht

Fixing bufferbloat with cerowrt: http://www.teklibre.com/cerowrt/subscribe.html