<div>I am interested in the case that the send and recieve buffer are the same buffer allocated from shared-memory, in which case there is no need for the data copying, send and recieve just only do the sync.</div> <div> </div> <div>A side question, when MPI_Send is called, does MPICH copy the data into a intermediate global buffer ? and have the data copy from this same buffer on MPI_Recv call ?</div> <div> </div> <div>tan</div> <div><BR><BR><B><I>Darius Buntinas <buntinas@mcs.anl.gov></I></B> wrote:</div> <BLOCKQUOTE class=replbq style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #1010ff 2px solid"><BR>Well, you specify one buffer in the call to MPI_Send and another buffer <BR>in MPI_Recv, so there would have to be at least one copy. You can't do <BR>it without any copies (otherwise, how would the data get from the send <BR>buffer to the receive buffer?).<BR><BR>MPICH2 does support communication over shared memory (as opposed to over
<BR>a network) which improves performance for intranode communication. <BR>Configure with --with-device=ch3:ssm or --with-device=ch3:nemesis.<BR><BR>Darius<BR><BR><BR>On 10/08/2007 12:22 PM, chong tan wrote:<BR>> If I the pointer passed to MPI_Send and MPI_Recieve are already shared <BR>> memory, and need not be copied at all ?<BR>> <BR>> If so, How ? <BR>> <BR>> thanks<BR>> tan<BR>> <BR>> <BR>> ------------------------------------------------------------------------<BR>> Be a better Heartthrob. Get better relationship answers <BR>> <HTTP: evt="48255/*http://answers.yahoo.com/dir/_ylc=X3oDMTI5MGx2aThyBF9TAzIxMTU1MDAzNTIEX3MDMzk2NTQ1MTAzBHNlYwNCQUJwaWxsYXJfTklfMzYwBHNsawNQcm9kdWN0X3F1ZXN0aW9uX3BhZ2U-?link=list&sid=396545433" us.rd.yahoo.com>from <BR>> someone who knows.<BR>> Yahoo! Answers - Check it out.<BR><BR></BLOCKQUOTE><BR><p> 
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