[ofa-general] Credit loops in infiniband networks and ibdm utility

[Keshetti Mahesh]

I have some basic questions about credit loops in infiniband
networks. Can anyone of you tell me in brief what are credit loops,
when they occur and how does IBDM utility verify the network for credit loops?
(I didn't find anything about credit loops in the IB spec.s)


 n2------S2\
             |    \
             |      \
             |        S1------ n1
             |      /
             |    /
  n3-----S3

In the above topology (S-switch and  n-node ), I have loaded all the
possible paths using the openSM's file based ucast manager.
When I ran an MPI job which sends data from both n3 and n1 to n2
I have observed a dead lock due to credit loop.  Why is it happening here ?

-Mahesh