Open MPI logo

Open MPI Development Mailing List Archives

  |   Home   |   Support   |   FAQ   |  

This web mail archive is frozen.

This page is part of a frozen web archive of this mailing list.

You can still navigate around this archive, but know that no new mails have been added to it since July of 2016.

Click here to be taken to the new web archives of this list; it includes all the mails that are in this frozen archive plus all new mails that have been sent to the list since it was migrated to the new archives.

Subject: Re: [OMPI devel] failure with zero-length Reduce() andbothsbuf=rbuf=NULL
From: Eugene Loh (Eugene.Loh_at_[hidden])
Date: 2010-02-10 11:42:43


Here is a related case.

If I remember correctly, the HPCC pingpong test synchronizes
occasionally by having one process send a zero-byte broadcast to all
other processes. What's a zero-byte broadcast? Well, some MPIs
apparently send no data, but do have synchronization semantics. (No
non-root process can exit before the root process has entered.) Other
MPIs treat the zero-byte broadcasts as no-ops; there is no
synchronization and then timing results from the HPCC pingpong test are
very misleading. So far as I can tell, the MPI standard doesn't address
which behavior is correct. The test strikes me as deficient: it would
have been just as easy to have a single-word broadcast to implement the
synchronization they were looking for.

Sigh.