[Users] PortXmitWait?

[Florent Parent]

On Thu, Mar 13, 2014 at 7:36 AM, Hal Rosenstock <hal.rosenstock at gmail.com>wrote:

> Some causes of congestion are: slow receiver, many to one communication,
> and "poor" fat tree topology.
>
> On the last item, are all links in the subnet same speed and width ?
>

Yes. Just verified the links, and everything is at 4x 10Gbps (QDR)


> How many links are used going up the fat tree to the next rank ?
>

Everything is configured as 1:1, except for 2 leaf switch connecting two of
our Lustre filesystems, where we have 2:1 blocking factor.
https://dl.dropboxusercontent.com/u/2292440/CQ-UL_IB_topology.pdf


>
> Are all end nodes connected to rank 2 or are any connected to higher rank ?
>

Everything is connected to rank2. There is an exception: The Sun blades are
connected to QNEM switches, which have "slibling links". Here's my attempt
to "ascii art":

12 nodes -- 12 links -- I4 -- 12 links -- M9 core sw.
                         |
                       9 links
                         |
12 nodes -- 12 links -- I4 -- 12 links -- M9 core sw.




>
> 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 ?
>

No. The only new addition are the 6 Lustre LNET routers on the CRAY system:
These nodes have 2 IB interfaces, but only one interface on the IB network
in quesetion. The other interface is connected to an IB switch isolated for
the CS300.  So these LNET routers are seen as one CA.

Florent


>
>
> On Wed, Mar 12, 2014 at 11:50 PM, Hal Rosenstock <hal.rosenstock at gmail.com
> > wrote:
>
>> 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.
>>
>> 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.
>>
>> 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 ?
>>
>> Any idea on what is the traffic pattern ? Are you running MPI ?
>>
>> -- Hal
>>
>>
>> On Wed, Mar 12, 2014 at 8:17 PM, Florent Parent <
>> florent.parent at calculquebec.ca> wrote:
>>
>>>
>>> Hello IB users,
>>>
>>> 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:
>>> General fabric topology info
>>> ============================
>>> - FatTree rank (roots to leaf switches): 3
>>> - FatTree max switch rank: 2
>>> - Fabric has 966 CAs, 966 CA ports (603 of them CNs), 186 switches
>>> - Fabric has 36 switches at rank 0 (roots)
>>> - Fabric has 64 switches at rank 1
>>> - Fabric has 86 switches at rank 2 (86 of them leafs)
>>>
>>> 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 ibqueryerrors.pl)
>>>
>>> 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):
>>>
>>> GUID 0x21283a83b30050 port 4:  PortXmitWait == 2932676  PortXmitData ==
>>> 90419517 (344.923MB)  PortRcvData == 1526963011 (5.688GB)
>>> GUID 0x21283a83b30050 port 5:  PortXmitWait == 3110105  PortXmitData ==
>>> 509580912 (1.898GB)  PortRcvData == 13622 (53.211KB)
>>> GUID 0x21283a83b30050 port 6:  PortXmitWait == 8696397  PortXmitData ==
>>> 480870802 (1.791GB)  PortRcvData == 17067 (66.668KB)
>>> GUID 0x21283a83b30050 port 7:  PortXmitWait == 1129568  PortXmitData ==
>>> 126483825 (482.497MB)  PortRcvData == 24973385 (95.266MB)
>>> GUID 0x21283a83b30050 port 8:  PortXmitWait == 29021  PortXmitData ==
>>> 19444902 (74.176MB)  PortRcvData == 84447725 (322.143MB)
>>> GUID 0x21283a83b30050 port 9:  PortXmitWait == 4945130  PortXmitData ==
>>> 161911244 (617.642MB)  PortRcvData == 27161 (106.098KB)
>>> GUID 0x21283a83b30050 port 10:  PortXmitWait == 16795  PortXmitData ==
>>> 35572510 (135.698MB)  PortRcvData == 681174731 (2.538GB)
>>> ... (this goes on for every active ports)
>>>
>>> We are not observing any failures, so I suspect that I need help to
>>> interpret these numbers. Do I need to be worried?
>>>
>>> Cheers,
>>> Florent
>>>
>>>
>>> _______________________________________________
>>> Users mailing list
>>> Users at lists.openfabrics.org
>>> http://lists.openfabrics.org/cgi-bin/mailman/listinfo/users
>>>
>>>
>>
>
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