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<p>Hello,</p>
<p>thanks for the quick feedback! It's not even TCP, that is what is
confusing me.</p>
<p>I attached two images. In this run, I am literally just pushing
UDP packets at 10mbit per second. The first run is kernel 4.18.
You can see that I am pushing in 10mbit on two interfaces and emit
10 mbit on the eth3. <br>
</p>
<p><img src="cid:part1.4672B10A.57ABA4C1@cs.ubc.ca" alt=""></p>
<p>Kernel 4.19 on the other hand looks like this: <img
src="cid:part2.0952D576.D3C9247C@cs.ubc.ca" alt=""></p>
<p>Optimal distribution 5/5 mbit on each interface. I am quite
confused.</p>
<p>I was hoping you guys might know, but it seems to be unrelated to
cake or the bufferbloat changes. I might just ask the netdev
guys. </p>
<p>Fabian<br>
</p>
<div class="moz-cite-prefix">On 11/22/18 1:15 PM, Stephen Hemminger
wrote:<br>
</div>
<blockquote type="cite" cite="mid:20181122131508.703f8b39@xeon-e3">
<pre class="moz-quote-pre" wrap="">On Thu, 22 Nov 2018 12:28:36 -0800
Fabian Ruffy <a class="moz-txt-link-rfc2396E" href="mailto:fruffy@cs.ubc.ca"><fruffy@cs.ubc.ca></a> wrote:
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">Hello,
this is a somewhat esoteric question. I am trying to actually force bufferbloat in an emulation setup I am using. I set up a dumbbell topology and push traffic through it, causing congestion at the central link. I use this setup to compare congestion avoidance algorithms such as DCTCP to other solutions.
This has worked nicely with the 4.18 kernel. However, after upgrading to 4.19 I cannot reproduce bufferbloat anymore. The traffic (even UDP packets) is perfectly rate limited and I never see any congestion happening. This is great, but in practice it prevents me from prototyping algorithms.
My interface configuration for bottlenecked links is:
qdisc tbf 5: dev OBcbnsw1-eth2 root refcnt 2 rate 10Mbit burst 15000b lat 12.0ms
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap=""> Sent 6042 bytes 51 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
qdisc netem 10: dev OBcbnsw1-eth2 parent 5:1 limit 500
Sent 6042 bytes 51 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
</pre>
</blockquote>
<pre class="moz-quote-pre" wrap="">
I have the suspicion that it is related to the CAKE changes in the 4.19 kernel, but I am not exactly sure. I am not using tc cake at all. Do you maybe know what could cause this behavior? Apologies if this is the wrong mailing list.
</pre>
</blockquote>
<pre class="moz-quote-pre" wrap="">
More likely it is a combination of TCP small queues and pacing support.
To emulate a network you need to have an intermediate box, otherwise the local feedback
in TCP will defeat what you are trying to do.
</pre>
</blockquote>
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