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<p class="MsoNormal">Hi,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I have two machines with a 10Gbits link with very low latency between them. I am using iperf to saturate the link and without introducing any latency I can saturate it with only 2 connections (-P parameter in iperf) to 9.90 Gbits/sec<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m using netem to introduce latency by configuring the interface in both machines like this: tc qdisc add dev eth0_0 root netem delay 1ms<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">With small latencies everything looks reasonable. For example for 5 ms in each direction I can saturate the link with 20 connections to 9.80 Bbits/sec. With higher values however, it goes downhill quite badly. With 10ms each side I can
barely get to 5 Gbits/sec, and with 20ms I can’t get to 2 Gbits/sec, no matter how many parallel connections I try.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m thinking that netem is introducing something different than just latency here. May it be possible that it is for example dropping frames because it can’t buffer enough at these speeds? Any suggestion to diagnose this?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal">Damian<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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