Hi Sébastien,

You can do better than 280 us.
Your hardware, is it Mellanox, QLogic or another one ?

In this case Mellanox ConnectX.


Are you using OFED ?

Yes.

So if you use

mpiexec -n 1024 Ray -test-network-only \
-route-messages -connection-type debruijn \
-routing-graph-degree 4


Then you get 4^5 = 1024, each rank has 4 connections instead of 2 and
routes are at most 5 hops.

Queued this test up.




But with the Kautz graph, it is harder to guess a number of cores.

One thing you can do is to allocate, for instance, 4096 cores with the
scheduler and only use 4032 with mpiexec.

64*63 is 4032 (degree= 63, diameter= 2, base= 64, vertices= 4032), but
that is a lot of cores !

Instead of having 4032 direct connections, each rank has exactly 63
connections and any rank can reach any other rank from the 4032 ranks in
at most 2 hops.

With 1 hop: 63 ranks reachable
With 2 hops: 3969 ranks reachable

The "1 hop" set and the "2 hops" set are disjoint.

63 + 3969 = 4032 ranks.

With the formula for kautz, n=(k+1)*k^(d-1), what values does one use for k and 
d? I have a cluster that has 480 cores (24 / node) that I'd like to test this 
on.

What does the "group" connection-type do?

Thanks,

Ben
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