On 03/06/2013 10:53 AM, Mathieu Bourgey wrote:
> Hi Sebastien,
>
> I would like to run a large job and when I read the ray documentation
> some points are not clear to me, probably due to my lack of MPI/graph
> knowledge.
> I was planing to use the polytope connection type, and I want to
> estimate which vertice and degree I should pass to ray. In the
> explanation you gave in the documentation you explain how to calcultate
> these two values:
> vertices:= alphabetSize^wordLength
> degree:= (alphabetSize-1)*wordLength
>
You may (or may not) need this virtual routing feature depending on where you
run your job.
> what I don't understand is what alphabetSize and wordlength represents ?
Documentation for this system is available in
https://github.com/sebhtml/ray/blob/master/Documentation/Routing.txt
I just updated the polytope documentation to used the words "Radix" and
"Dimension".
Alphabet size is the radix (the number of possible values in each
dimension) whereas the word length is the number of dimensions.
For example, a cube is a polytope with a radix of 2 and a dimension of 3.
The number of vertices of a cube is 2 power 3, which is 8. The degree of
a cube is (2-1) * 3 = 3 -- each vertex of a cube is connected to 3 vertices.
>
> I already have an estimation of what the maximum vertice I could reach
> based on the reasonnable number of core*cpu I could ask to do not stay
> in queue for to long. For information I was planning asking 85 cores of
> 24cpu (in the mamouth HPC) so my number of vertice would be max 2040.
>
> can you give me more details or tips on that point ?
>
Sure.
On some supercomputers, like Mammouth in Sherbrooke, Canada, the interconnect is
Infiniband, but there seems to be too many direct connections for each HCA
(Host Communication
Adapter). I have some hypotheses to explain this, but I don't have substantial
support for
any of these hypotheses.
However, using virtual message routing fixes the problem of very high latencies
or MPI_ERR_OTHER.
With 2040 cores (that is 85 nodes with 24 cores each), the nearest polytope is
the one with 2
dimensions and a radix of 45. Its number of vertices is 45 power 2, or 2025.
Its degree is 88 ((2-1)*45).
From the updated polytope documentation (Routing.txt):
Vertices: 2025 (45 ^ 2)
Type: Polytope
Radix: 45
Dimension: 2
Degree: 88 ((45 - 1 ) * 2)
Options: -route-messages -connection-type polytope -routing-graph-degree 88
> Thanks in advance
You are welcomed.
>
> Mathieu
>
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