[mpi3-coll] array parameters in nonblocking collectives

[Rajeev Thakur]

Torsten,
        What does libNBC do in this case?

Rajeev
 

> -----Original Message-----
> From: mpi3-coll-bounces at lists.mpi-forum.org 
> [mailto:mpi3-coll-bounces at lists.mpi-forum.org] On Behalf Of 
> Torsten Hoefler
> Sent: Saturday, August 01, 2009 10:46 AM
> To: MPI-3 Collective Subgroup Discussions
> Subject: Re: [mpi3-coll] array parameters in nonblocking collectives
> 
> Hello Bin,
> thanks for bringing this up Bin, it seems like an important issue.
> 
> I can see both sides. In general, I would say that all vector 
> collectives are not scalable anyway because they require 
> \Theta(P) memory per node and \Theta(P^2) total. Shifting 
> this by a constant factor probably doesn't matter too much 
> for asymptotic (large-scale) analysis. However, there is 
> certainly a border-zone where something could be gained with 
> transferring the ownership of the arrays. 
> 
> We will certainly discuss this issue in Helsinki and at the 
> next telecon!
> 
> For the future, I would generally expect that, at large 
> scale, such communications are rather sparse. So we should 
> either talk about a sparse interface to vector collectives or 
> its static variant, the graph topology collectives. Those 
> options will also be discussed asap. Both options would 
> potentially reduce the total memory consumption (assuming 
> sparse communications) from \Theta(P^2) to O(P) or O(P 
> log(P)) depending on the problem.
> 
> All the Best,
>   Torsten
> 
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