That would make sense. I able to break OpenMPI by having Node A wait for messages from Node B. Node B is in fact sleeping while Node C bombards Node A with a few thousand messages. After a while Node B wakes up and sends Node A the message it's been waiting on, but Node A has long since been buried and seg faults. If I decrease the number of messages C is sending, it works properly. This was on OpenMPI 1.2.4 (using I think the SM BTL (might have been MX or TCP, but certainly not infiniband. I could dig up the test and try again if anyone is seriously curious).
Trying the same test on MPICH/MX went very very slow (I don't think they have any clever buffer management) but it didn't crash. Sacerdoti, Federico Federico.Sacerdoti-at-deshaw.com |openmpi-users/Allow| wrote: > Hi, > > I am readying an openmpi 1.2.5 software stack for use with a > many-thousand core cluster. I have a question about sending small > messages that I hope can be answered on this list. > > I was under the impression that if node A wants to send a small MPI > message to node B, it must have a credit to do so. The credit assures A > that B has enough buffer space to accept the message. Credits are > required by the mpi layer regardless of the BTL transport layer used. > > I have been told by a Voltaire tech that this is not so, the credits are > used by the infiniband transport layer to reliably send a message, and > is not an openmpi feature. > > Thanks, > Federico > > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users -- --Kris 叶ってしまう夢は本当の夢と言えん。 [A dream that comes true can't really be called a dream.]
