Hi again,<div><br></div><div>Today I was trying with another TCP benchmark included in the hpcbench suite, and with a ping-pong test I&#39;m also getting 100us of latency. Then, I tried with netperf and the same result....</div>
<div><br></div><div>So, in summary, I&#39;m measuring TCP latency with messages size between 1-32 bytes:</div><div><br></div><div>Netperf over TCP                     -&gt; 100us</div><div>Netpipe over TCP (NPtcp)        -&gt; 100us</div>
<div>HPCbench over TCP                -&gt; 100us</div><div>Netpipe over OpenMPI (NPmpi) -&gt; 60us</div><div>HPCBench over OpenMPI         -&gt; 60us</div><div><br></div><div>Any clues?</div><div><br></div><div>Thanks a lot!<br>
<br><div class="gmail_quote">2012/1/10 Roberto Rey <span dir="ltr">&lt;<a href="mailto:eros.83@gmail.com">eros.83@gmail.com</a>&gt;</span><br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hi,<div><br></div><div>I&#39;m running some tests on EC2 cluster instances with 10 Gigabit Ethernet hardware and I&#39;m getting strange latency results with Netpipe and OpenMPI. </div><div><br></div><div>If I run Netpipe over OpenMPI (NPmpi) I get a network latency around 60 microseconds for small messages (less than 2kbytes). However, when I run Netpipe over TCP (NPtcp) I always get around 100 microseconds. For bigger messages everything seems to be OK.</div>

<div><br></div><div>I&#39;m using the BTL TCP in OpenMPI, so I can&#39;t understand why OpenMPI outperforms raw TCP performance for small messages (40us of difference). I also have run the PingPong test from the Intel Media Benchmarks and the latency results for OpenMPI are very similar (60us) to those obtained with NPmpi</div>

<div><br></div><div>Can OpenMPI outperform Netpipe over TCP? Why? Is OpenMPI  doing any optimization in BTL TCP?</div><div><br></div><div>The results for OpenMPI aren&#39;t so good but we must take into account the network virtualization overhead under Xen</div>

<div><br></div><div>
<span style="font-family:verdana,arial,helvetica;font-size:12px">Thanks for your reply</span>
</div>
</blockquote></div><br><br clear="all"><div><br></div>-- <br>Roberto Rey Expósito<br>
</div>