Hmmm...just to be sure we are all clear on this. The reason we
proposed to use mpirun is that "hostfile" has no meaning outside of
mpirun. That's why ompi_info can't do anything in this regard.
We have no idea what hostfile the user may specify until we actually
get the mpirun cmd line. They may have specified a default-hostfile,
but they could also specify hostfiles for the individual app_contexts.
These may or may not include the node upon which mpirun is executing.
So the only way to provide you with a separate command to get a
hostfile<->nodename mapping would require you to provide us with the
default-hostifle and/or hostfile cmd line options just as if you were
issuing the mpirun cmd. We just wouldn't launch - but it would be the
exact equivalent of doing "mpirun --do-not-launch".
Am I missing something? If so, please do correct me - I would be happy
to provide a tool if that would make it easier. Just not sure what
that tool would do.
Thanks
Ralph
On Oct 19, 2008, at 1:59 PM, Greg Watson wrote:
Ralph,
It seems a little strange to be using mpirun for this, but barring
providing a separate command, or using ompi_info, I think this would
solve our problem.
Thanks,
Greg
On Oct 17, 2008, at 10:46 AM, Ralph Castain wrote:
Sorry for delay - had to ponder this one for awhile.
Jeff and I agree that adding something to ompi_info would not be a
good idea. Ompi_info has no knowledge or understanding of
hostfiles, and adding that capability to it would be a major
distortion of its intended use.
However, we think we can offer an alternative that might better
solve the problem. Remember, we now treat hostfiles in a very
different manner than before - see the wiki page for a complete
description, or "man orte_hosts".
So the problem is that, to provide you with what you want, we need
to "dump" the information from whatever default-hostfile was
provided, and, if no default-hostfile was provided, then the
information from each hostfile that was provided with an app_context.
The best way we could think of to do this is to add another mpirun
cmd line option --dump-hostfiles that would output the line-by-line
name from the hostfile plus the name we resolved it to. Of course,
--xml would cause it to be in xml format.
Would that meet your needs?
Ralph
On Oct 15, 2008, at 3:12 PM, Greg Watson wrote:
Hi Ralph,
We've been discussing this back and forth a bit internally and
don't really see an easy solution. Our problem is that Eclipse is
not running on the head node, so gethostbyname will not
necessarily resolve to the same address. For example, the hostfile
might refer to the head node by an internal network address that
is not visible to the outside world. Since gethostname also looks
in /etc/hosts, it may resolve locally but not on a remote system.
The only think I can think of would be, rather than us reading the
hostfile directly as we do now, to provide an option to ompi_info
that would dump the hostfile using the same rules that you apply
when you're using the hostfile. Would that be feasible?
Greg
On Sep 22, 2008, at 4:25 PM, Ralph Castain wrote:
Sorry for delay - was on vacation and am now trying to work my
way back to the surface.
I'm not sure I can fix this one for two reasons:
1. In general, OMPI doesn't really care what name is used for the
node. However, the problem is that it needs to be consistent. In
this case, ORTE has already used the name returned by gethostname
to create its session directory structure long before mpirun
reads a hostfile. This is why we retain the value from
gethostname instead of allowing it to be overwritten by the name
in whatever allocation we are given. Using the name in hostfile
would require that I either find some way to remember any prior
name, or that I tear down and rebuild the session directory tree
- neither seems attractive nor simple (e.g., what happens when
the user provides multiple entries in the hostfile for the node,
each with a different IP address based on another interface in
that node? Sounds crazy, but we have already seen it done - which
one do I use?).
2. We don't actually store the hostfile info anywhere - we just
use it and forget it. For us to add an XML attribute containing
any hostfile-related info would therefore require us to re-read
the hostfile. I could have it do that -only- in the case of "XML
output required", but it seems rather ugly.
An alternative might be for you to simply do a "gethostbyname"
lookup of the IP address or hostname to see if it matches instead
of just doing a strcmp. This is what we have to do internally as
we frequently have problems with FQDN vs. non-FQDN vs. IP
addresses etc. If the local OS hasn't cached the IP address for
the node in question it can take a little time to DNS resolve it,
but otherwise works fine.
I can point you to the code in OPAL that we use - I would think
something similar would be easy to implement in your code and
would readily solve the problem.
Ralph
On Sep 19, 2008, at 7:18 AM, Greg Watson wrote:
Ralph,
The problem we're seeing is just with the head node. If I
specify a particular IP address for the head node in the
hostfile, it gets changed to the FQDN when displayed in the map.
This is a problem for us as we need to be able to match the two,
and since we're not necessarily running on the head node, we
can't always do the same resolution you're doing.
Would it be possible to use the same address that is specified
in the hostfile, or alternatively provide an XML attribute that
contains this information?
Thanks,
Greg
On Sep 11, 2008, at 9:06 AM, Ralph Castain wrote:
Not in that regard, depending upon what you mean by "recently".
The only changes I am aware of wrt nodes consisted of some
changes to the order in which we use the nodes when specified
by hostfile or -host, and a little #if protectionism needed by
Brian for the Cray port.
Are you seeing this for every node? Reason I ask: I can't
offhand think of anything in the code base that would replace a
host name with the FQDN because we don't get that info for
remote nodes. The only exception is the head node (where mpirun
sits) - in that lone case, we default to the name returned to
us by gethostname(). We do that because the head node is
frequently accessible on a more global basis than the compute
nodes - thus, the FQDN is required to ensure that there is no
address confusion on the network.
If the user refers to compute nodes in a hostfile or -host (or
in an allocation from a resource manager) by non-FQDN, we just
assume they know what they are doing and the name will
correctly resolve to a unique address.
On Sep 10, 2008, at 9:45 AM, Greg Watson wrote:
Hi,
Has there been a change in the behavior of the -display-map
option has changed recently in the 1.3 branch. We're now
seeing the host name as a fully resolved DN rather than the
entry that was specified in the hostfile. Is there any
particular reason for this? If so, would it be possible to add
the hostfile entry to the output since we need to be able to
match the two?
Thanks,
Greg
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