Gilad Shainer wrote:
There was a nice debate on message rate, how important is this factor
when you
Want to make a decision, what are the real application needs, and if
this is
just a marketing propaganda. For sure, the message rate numbers that are
listed
on Greg web site regarding other interconnects are wrong.
I would take a look on the new cluster in Tokyo institute of technology.
The
Servers there are "fat nodes" too.
Not to try to inject an application centric view into the middle of a
theoretical debate ...
We have some nice data from November 2005 directly comparing the
performance of single thread per node to multi-thread per node on a
system with both Myrinet and Infinipath HTX units in there. I don't
have the data in front of me, but I can recall some of the features.
For LAMMPS running on this cluster we saw a definite degradation which
we ascribed to resource contention after doing more tests, when more
than 1 thread per node ran. With 2 threads per node, it was a noticable
impact on all interconnects. Something in the 5-10% region. At one
thread per core (4 cores in 2 sockets), we were seeing significant
performance impact from this contention. We ran the same tests on an 8
core system and myrinet and the performance impact was more than
"noticable". Ran the 4 thread test on 1,2,4 systems, and the 4 way
using the infinipath, the myrinet, ch_p4, and ch_shmem using MPICH 1.2.7.
We didn't have time to investigate message size or messaging rate. What
we did find was for this code using this input deck, on these systems,
running one thread per node gave us the best performance, and one thread
per socket was already showing performance degradation. One thread per
core on the dual cores was showing significant performance degradation
on infinipath and myrinet, but not ch_shmem. ch_p4 was simply a baseline.
Someday it would be nice to explore this again with a range of other codes.
Joe
Gilad.
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