[Bloat] troubles with congestion (tbf vs htb)

[Dave Taht]

Dear Davide:

sounds like a job for the bloat list. I note your attachment got
filtered out on your
posting to netdev.

None of what you describe surprises me, but I would love to duplicate
your tests, exactly, against the new 3.3 kernel, which has BQL and
various active AQMs, and I also remember various things
around ssthresh being fiddled with over the past year.

On Fri, Mar 9, 2012 at 1:50 PM, Davide Gerhard <rainbow at irh.it> wrote:
> Hi,
> I am a master's student from the university of Trento, I have been doing a
> project, for the course of advanced networking (In a group of 2), focused
> on the TCP congestion control. I used tc with htb to simulate a link with
> 10mbit/s using a 100mbit/s real ethernet lan. Here is the code I used:
>
> tc qdisc add dev $INTF root handle 1: netem $DELAY $LOSS $DUPLICATE
>  $CORRUPT $REORDENING
> tc qdisc add dev $INTF parent 1:1 handle 10: htb default 1 r2q 10
> tc class add dev $INTF parent 10: classid 0:1 htb rate ${BANDW}kbit ceil
>  ${BANDW}kbit
>
> and here is the topology
>
> client -->|    |--> server with iperf -s
>          |    |
>          |    |
>          +    +
>           eth0
>    CONGESTION machine
>
> The congestion machine have the following configurations:
> - kernel 3.0
> - echo 1 > /proc/sys/net/ipv4/ip_forward
> - echo 0 > /proc/sys/net/ipv4/conf/default/send_redirects
> - echo 0 > /proc/sys/net/ipv4/conf/all/send_redirects
> - echo 1 > /proc/sys/net/ipv4/ip_no_pmtu_disc
> - echo 0 > /proc/sys/net/ipv4/conf/eth0/send_redirects
>
> The client captures the window size and ssthresh with tcp_flow_spy but we do
> not see any changes in the ssthresh and the window size is too large
> compared to the bandwidth*latency product (see attachment). In a normal scenario,
> this would be acceptable (I guess), but in order to obtain some relevant
> results for our work, we need to avoid this "buffer" and to activate
> the ssthresh. I have already tried to change backlog but this does
> not change anything. I have also tried to use tbf with the following command:
>
> tc qdisc add dev $INTF parent 1:1 handle 10: ftb rate ${BANDW}kbit burst 10kb
>  latency 1.2ms minburst 1540
>
> In this case, the congestion works correctly as we expect, but if we use
> netem I have to recalculate again all the needed values (correct?). Are there
> any other solutions?
>
> Best regards.
> /davide
>
> P.S Here follows the sysctl parameters used in the client:
> net.ipv4.tcp_no_metrics_save=1
> net.ipv4.tcp_sack=1
> net.ipv4.tcp_dsack=1
>
> --
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> of the wise and humane surgeon." - Sir John Eric Ericksen, British surgeon,
> appointed Surgeon-Extraordinary to Queen Victoria 1873
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-- 
Dave Täht
SKYPE: davetaht
US Tel: 1-239-829-5608
http://www.bufferbloat.net