[MPICH] Can I ask MPI to not copy the data to shared-mem ?

[chong tan]

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.
   
  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 ?
   
  tan
  

Darius Buntinas <buntinas at mcs.anl.gov> wrote:
  
Well, you specify one buffer in the call to MPI_Send and another buffer 
in MPI_Recv, so there would have to be at least one copy. You can't do 
it without any copies (otherwise, how would the data get from the send 
buffer to the receive buffer?).

MPICH2 does support communication over shared memory (as opposed to over 
a network) which improves performance for intranode communication. 
Configure with --with-device=ch3:ssm or --with-device=ch3:nemesis.

Darius


On 10/08/2007 12:22 PM, chong tan wrote:
> If I the pointer passed to MPI_Send and MPI_Recieve are already shared 
> memory, and need not be copied at all ?
> 
> If so, How ? 
> 
> thanks
> tan
> 
> 
> ------------------------------------------------------------------------
> Be a better Heartthrob. Get better relationship answers 
> from 
> someone who knows.
> Yahoo! Answers - Check it out.



       
---------------------------------
Need a vacation? Get great deals to amazing places on Yahoo! Travel. 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/mpich-discuss/attachments/20071008/fcaa5253/attachment.htm>