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Subject: Re: [OMPI users] scaling problem with openmpi
From: Pavel Shamis (Pasha) (pashash_at_[hidden])
Date: 2009-05-20 12:45:53


> Disabling basic_linear seems like a good idea but your config file sets the
> cut-off at 128 Bytes for 64-ranks (the field you set to 8192 seems to result
> in a message size of that value divided by the number of ranks).
>
> In my testing bruck seems to win clearly (at least for 64 ranks on my IB) up
> to 2048. Hence, the following line may be better:
>
> 131072 2 0 0 # switch to pair wise for size 128K/nranks
>
> Disclaimer: I guess this could differ quite a bit for nranks!=64 and different
> btls.
>
Sounds strange for me. From the code is looks that we take the threshold as
is without dividing by number of ranks.

Pasha,