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From: Pak Lui (Pak.Lui_at_[hidden])
Date: 2006-05-31 15:31:33

Ralph Castain wrote:
> Hi Pak
> I'm afraid I don't fully understand your question, so forgive me if I
> don't seem to address the problem adequately. As I understand it, you
> are asking about the scenario where someone wants to execute multiple
> calls of mpirun, with the applications executing on the same set of
> nodes. Your question is: why does OpenRTE spawn a new daemon (orted) on
> the node each time we execute mpirun - why doesn't it just use the
> existing one to launch the new application process(es)?
> Assuming I have the question right, the short answers are "may not be
> permitted" and "not yet implemented". :-)

yes, Ralph, that is precisely the question. good thing that you've
figured that out :)

> First, the fact that an orted already exists on a node is not sufficient
> to allow us to use it again for another application. The orted must be
> persistent or else we do not allow a new application to re-use it. This
> is required because the existing orted will go away when its original
> application is done executing - if we use it as our parent to launch
> another child, then the new application process will "die" when the
> original one completes. Obviously, that isn't desirable.

okay. I used to think that if orted is able to stay and fork other
processes, but I didn't realize orted will go away once the parent
process finishes.

> Second, even though you can launch persistent orteds today, none of the
> current components in the resource management subsystems actually know
> how to use them yet. This is something we planned to implement in the
> future, but there simply hasn't been time to do so yet.
> So the bottom line is that there really is no way around the need to
> launch a new orted on each node every time the user issues an mpirun
> command.
> I hope that answers your question. If not, please don't hesitate to let
> me know.

Thanks for pointing out these issues. I was hoping something I didn't
know may solve my problem. I guess there may not be a good workaround
for this limitation due to SGE slots. We could try to track and set some
top limit for the number of times that qrsh can exec, before the spawn
program uses up all the available SGE slots and errors out.

> Ralph
> Pak Lui wrote:
>> Hi,
>> When I run a spawn program over rsh/ssh, I notice that each time the
>> child program gets spawned, it will need to establish a new rsh/ssh
>> connection to the remote node to launch orted on that node, even the
>> parent executable and the orted are running on that node.
>> So I wonder if there is any way that we can use the parent orted to
>> launch the child program if they happen to be on the same node?
>> I try to compare to the spawn program to the scenario where I run
>> multiple executables in one mpirun command. For this run, I only
>> establish one connection to the remote node only, and both executables
>> shared the same remote connection.
>> % ./mpirun -np 2 -host burl-ct-v440-5 -prefix `pwd`/.. sleep 12 : -np 2
>> sleep 10
>> Password:
>> 15015 /workspace/paklui/ompi/trunk/builds/sparc32-g/bin/../bin/orted
>> --bootprox
>> 15017 sleep 12
>> 15019 sleep 12
>> 15021 sleep 10
>> 15023 sleep 10
>> The reason that I want to find out if it is possible for orted to
>> launch child executable(s) without having to establish a new
>> connection, is because the number of times that I can run 'qrsh' in
>> SGE (or N1GE) is actually depended on the number of slots that the
>> user initially allocated. That the slot number corresponds to the
>> number of CPUs on a node. Each slot allows one 'qrsh' connection.
>> The issue is when I try to run a spawn job on a single node, or a
>> cluster of many 1-cpu nodes under SGE. The number of times that the
>> program can spawn is limited by 'qrsh', that it forbids the child
>> program to connect to the same node where the parent executable's
>> orted might be already running there.
>> I am curious to see if I can find some solution to the problem here. I
>> am also looking to see if there are some tricks in SGE to get around
>> this issue, but workaround I can see aren't pretty though. So I
>> welcome your questions, comments or suggestions on this.

- Pak Lui