Newsgroups: comp.parallel.mpi
From: Anand Pillai <anand@ERC.MsState.Edu>
Subject: Re: Non-blocking sends
Organization: NSF-Engineering Research Center for Computational Field Simulation
Date: Wed, 23 Jul 1997 15:06:29 -0500
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Message-ID: <Pine.GSO.3.96.970723150341.10466A-100000@moccasin>

>   Rationale:
>   We prohibit read accesses to a send buffer while it is being used, 
>   even though the send operation is not supposed to alter the content
>   of this buffer. This may seem more restrictive than necessary, but the
>   additional restriction causes little loss of functionality, and allows
>   better performance on some systems - consider the case where data
>   transfer is done by a DMA engine that is not cache coherent with the
>   main processor. (End of Rationale).

Can someone explain to me why it is not possible to read a send buffer in
this case (data transfer through DMA)? I don't fully understand the
problem when data transfer is done through DMA. 

Thanks
Anand