<div dir="ltr"><div>Some causes of congestion are: slow receiver, many to one communication, and "poor" fat tree topology.</div><div> </div><div>On the last item, are all links in the subnet same speed and width ? How many links are used going up the fat tree to the next rank ?</div>
<div> </div><div>Are all end nodes connected to rank 2 or are any connected to higher rank ?</div><div> </div><div>Are there any "combined" nodes ? By this I mean, some device which is more than just single switch or CA. If so, what are they and where do they live in the topology ?</div>
</div><div class="gmail_extra"><br><br><div class="gmail_quote">On Wed, Mar 12, 2014 at 11:50 PM, Hal Rosenstock <span dir="ltr"><<a href="mailto:hal.rosenstock@gmail.com" target="_blank">hal.rosenstock@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div>By the fact that you didn't mention PortXmitDiscards, does it mean that these are 0 ? Assuming so, PortXmitWait is indicating there is some congestion but it has not risen to the level of dropping packets. It's the rate of increase of the XmitWait counter that's important rather than the absolute number so if you want to chase this, the focus should be on the ports most congested.</div>
<div> </div><div>Since the old tool didn't report XmitWait counters, it's hard to know whether this is the same as before or not unless you did this manually.</div><div> </div><div>Was the routing previously fat tree ? Are there any other fat tree related log messages in the OpenSM log ? Is there any fat tree configuration of compute and/or I/O nodes ?</div>
<div> </div><div>Any idea on what is the traffic pattern ? Are you running MPI ?</div><span class="HOEnZb"><font color="#888888"><div> </div><div>-- Hal</div></font></span></div><div class="gmail_extra"><br><br><div class="gmail_quote">
<div><div class="h5">On Wed, Mar 12, 2014 at 8:17 PM, Florent Parent <span dir="ltr"><<a href="mailto:florent.parent@calculquebec.ca" target="_blank">florent.parent@calculquebec.ca</a>></span> wrote:<br>
</div></div><blockquote style="margin:0px 0px 0px 0.8ex;padding-left:1ex;border-left-color:rgb(204,204,204);border-left-width:1px;border-left-style:solid" class="gmail_quote"><div><div class="h5"><div dir="ltr"><div><br>
</div>Hello IB users,<br><div><div><br></div><div>We recently migrated our opensm from 3.2.6 to 3.3.17. In this upgrade, we moved to CentOS6.5 with the stock RDMA and infiniband-diags_1.5.12-5., and running opensm 3.3.17. Routing is FatTree:</div>
<div><div>General fabric topology info</div><div>============================</div><div>- FatTree rank (roots to leaf switches): 3</div><div>- FatTree max switch rank: 2</div><div>- Fabric has 966 CAs, 966 CA ports (603 of them CNs), 186 switches</div>
<div>- Fabric has 36 switches at rank 0 (roots)</div><div>- Fabric has 64 switches at rank 1</div><div>- Fabric has 86 switches at rank 2 (86 of them leafs)</div></div><div><br></div><div>Now to the question: ibqueryerrors 1.5.12 is reporting high PortXmitWait values throughout the fabric. We did not see this counter before (it was not reported by the older <a href="http://ibqueryerrors.pl" target="_blank">ibqueryerrors.pl</a>)</div>
<div><br></div><div>To give an idea of the scale of the counters, here's a capture of ibqueryerrors --data on one specific I4 switch, 10 seconds after clearing the counters (-k -K):</div><div><br></div><div>GUID 0x21283a83b30050 port 4: PortXmitWait == 2932676 PortXmitData == 90419517 (344.923MB) PortRcvData == 1526963011 (5.688GB)</div>
<div>GUID 0x21283a83b30050 port 5: PortXmitWait == 3110105 PortXmitData == 509580912 (1.898GB) PortRcvData == 13622 (53.211KB)</div><div>GUID 0x21283a83b30050 port 6: PortXmitWait == 8696397 PortXmitData == 480870802 (1.791GB) PortRcvData == 17067 (66.668KB)</div>
<div>GUID 0x21283a83b30050 port 7: PortXmitWait == 1129568 PortXmitData == 126483825 (482.497MB) PortRcvData == 24973385 (95.266MB)</div><div>GUID 0x21283a83b30050 port 8: PortXmitWait == 29021 PortXmitData == 19444902 (74.176MB) PortRcvData == 84447725 (322.143MB)</div>
<div>GUID 0x21283a83b30050 port 9: PortXmitWait == 4945130 PortXmitData == 161911244 (617.642MB) PortRcvData == 27161 (106.098KB)</div><div>GUID 0x21283a83b30050 port 10: PortXmitWait == 16795 PortXmitData == 35572510 (135.698MB) PortRcvData == 681174731 (2.538GB)</div>
<div>... (this goes on for every active ports)</div><div><br></div><div>We are not observing any failures, so I suspect that I need help to interpret these numbers. Do I need to be worried? </div><div><br></div><div>Cheers,</div>
<div>Florent</div></div><div><br></div></div>
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