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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