Newsgroups: comp.parallel.mpi
From: lederman@romano.cs.wisc.edu (Steve Huss-Lederman)
Subject: Re: is synchronous and ready mode necessarily non-buffered?
Organization: CS Department, University of Wisconsin
Date: 15 Dec 1995 14:54:30 GMT
Message-ID: <LEDERMAN.95Dec15085430@romano.cs.wisc.edu>

The MPI standard deliberately does not state whether buffering will
occur.  Though it is likely that no buffering occurs in synchronous
mode, I believe it is allowed.  It would be an unusual implementation
that would copy out of user space into system space to then wait until
the receive is posted to complete the send but I think it is allowed.
In ready mode it can certainly happen.  An implementation can use
regular sends whenever it gets a ready send.  This might not be as
efficient but could be done.  Thus, if regular sends buffer then ready
would too (assuming it does it when the recv is already posted).

Steve

