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Subject: Re: [OMPI devel] RFC: change default for tuned alltoallv to pairwise
From: Shamis, Pavel (shamisp_at_[hidden])
Date: 2012-03-22 15:56:35

>> What: Change coll tuned default to pairwise exchange
>> Why: The linear algorithm does not scale to any reasonable number of PEs
>> When: Timeout in 2 days (Fri)
>> Is there any reason the default should not be changed?
> Nathan,
> I can see why people think the linear algorithm is bad. However I think it depends on the application communication pattern in the alltoallv. Do you have any numbers to back your claim?

In addition the above list of dependencies it also depends on network technology. The linear algorithm does not play well with IB.