Here is what the MPI standard state:
"In general, message passing calls do not modify the value of the
error code field of status variables. This field may be updated
only
by the functions in Section 3.7.5 which return multiple statuses.
The
field is updated if and only if such function returns with an
error
code of MPI ERR IN STATUS.
Rationale. The error field in status is not needed for calls that
return only one status, such as MPI WAIT, since that would only
duplicate the information returned by the function itself. The
current
design avoids the additional overhead of setting it, in such
cases.
The field is needed for calls that return multiple statuses, since
each request may have had a different failure. (End of
rationale.)"
First, the sentence start with "In general" which is not a
limiting
statement, it absolutely doesn't state that the field doesn't have
to
be set. Second, the reason cited in the rationale is completely
fake.
We're talking about one store instruction, while the simple
usage of
the status will generate a cache miss.
On the other side, a simple grep in the ompi-tests shows that
hundreds
of tests use this MPI_ERROR over the return value. If test writers
(which are supposed to know the standard quite well), do such
things,
I wonder how can we expect that the users will never do it.
george.
On Jun 6, 2008, at 12:04 PM, Brian Barrett wrote:
Since this is not the first or second time we've had the
discussion in
the group, perhaps a comment in the code would be a good idea :).
Brian
On Jun 6, 2008, at 9:58 AM, Jeff Squyres wrote:
George --
This is not correct. Note the comment that says to see MPI-1.2
section 3.2.5 page 22 (I think it means MPI-1.1). It says:
"In general, message passing calls do not modify the value of
the
error code field of status variables. This field may be updated
only
by the functions in Section 3.7.5 which return multiple
statuses."
So we should not be setting status.MPI_ERROR here; you should
check
the return value from MPI_WAIT to get the error code.
On Jun 6, 2008, at 11:53 AM, bosi...@osl.iu.edu wrote:
Author: bosilca
Date: 2008-06-06 11:53:17 EDT (Fri, 06 Jun 2008)
New Revision: 18607
URL: https://svn.open-mpi.org/trac/ompi/changeset/18607
Log:
Update the MPI_ERROR field as well.
Text files modified:
trunk/ompi/request/req_wait.c | 1 +
1 files changed, 1 insertions(+), 0 deletions(-)
Modified: trunk/ompi/request/req_wait.c
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
===============================================================
--- trunk/ompi/request/req_wait.c (original)
+++ trunk/ompi/request/req_wait.c 2008-06-06 11:53:17 EDT (Fri,
06
Jun 2008)
@@ -50,6 +50,7 @@
/* See MPI-1.2, sec 3.2.5, p.22 */
status->MPI_TAG = req->req_status.MPI_TAG;
status->MPI_SOURCE = req->req_status.MPI_SOURCE;
+ status->MPI_ERROR = req->req_status.MPI_ERROR;
status->_count = req->req_status._count;
status->_cancelled = req->req_status._cancelled;
}
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Jeff Squyres
Cisco Systems
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Brian Barrett
Open MPI developer
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