On a LAN, window sizes aren&#39;t going to make that much of a difference.<div><br></div><div>First look for the usual suspects - errors on the swich port or NIC.</div><div><br></div><div>If you can grab a copy of the traffic, such as with tcpdump -w test.pcap tcp port 5001, you can pull it into wireshark and look for TCP zero window conditions, retransmits, and duplicate ACKs. The TCP performance graph will also show whether or not the transmission is stalling.</div>
<div><br></div><div>Is the performance similar using the UDP test? Does it show loss?</div><div><br></div><div>Sean<br><br><div class="gmail_quote">On Mon, Apr 5, 2010 at 7:27 PM, Kevin McGregor <span dir="ltr">&lt;<a href="mailto:kevin.a.mcgregor@gmail.com">kevin.a.mcgregor@gmail.com</a>&gt;</span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">I&#39;ve been trying to narrow down where my performance bottleneck(s) is (are). I just ran &quot;iperf&quot; from a Windows PC (XP SP3) to my Ubuntu 9.10 server. With iperf in &quot;server&quot; mode on the PC, and the client running on the Ubuntu machine, I get<div>

 0.0-60.0 sec  4.23 GBytes   606 Mbits/sec</div><div><br></div><div>Reversed (iperf &quot;server&quot; running on Ubuntu server, client running on the PC), I get</div><div> 0.0-60.0 sec  1.13 GBytes   162 Mbits/sec</div>
<div>
<br></div><div>Wha...?? Both client and server runs on the PC report TCP window size to be 8 KB, but the Linux client reports 22.4 KB and the Linux server reports 85.3 KB. Increasing that to 256K on both ends has little effect. Does anyone have any suggestions?</div>

<div><br></div><div>The Windows NIC is a Realtek RTL8169/8110 Family Gigabit Ethernet; the Ubuntu server is using the Realtek Semiconductor Co., Ltd. RTL8111/8168B PCI Express Gigabit Ethernet controller (rev 01). Time to replace a NIC or two?</div>

<div><br></div><font color="#888888"><div>Kevin</div>
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<br></blockquote></div><br><br clear="all"><br>-- <br>Sean Walberg &lt;<a href="mailto:sean@ertw.com">sean@ertw.com</a>&gt;    <a href="http://ertw.com/">http://ertw.com/</a><br>
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