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Subject: Re: [OMPI devel] Open IB BTL and iWARP
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2008-07-09 17:04:50


On Jul 9, 2008, at 4:08 PM, Don Kerr wrote:

> Last I looked the OpenIB BTL relied on the short eager rdma buffers
> being written in order? Is this still the case?

The eager rdma optimization relies on the last byte of the short
message being written last. I.e., when we see the last byte in the
target buffer, we assume the rest of the message is there.

> If so, how is this handled when iWARP is underneath the User Verb
> API and not Mellonox IB HCAs?

There's an MCA parameter that disables this optimization if the
underlying hardware can't provide that guarantee. We also have this
field in the INI file so that specific adapters can disable it
automatically if they want/need to.

Chelsio T3, NetEffect NE020, and NetXen adapters can all provide that
guarantee (I asked those vendors). You can see this in:

https://svn.open-mpi.org/trac/ompi/browser/trunk/ompi/mca/btl/openib/mca-btl-openib-hca-params.ini

-- 
Jeff Squyres
Cisco Systems