Brief summary: In r18190, I have restored the --do-not-launch capability, and added a --do-not-resolve flag. This note describes how you can use those to build and test application mappings without first getting an allocation and/or launching it.
Longer description: Users and developers have both expressed a need to develop potentially complex process mappings "offline" - i.e., before attempting to actually launch the application. This has been particularly problematic when the mappings are large and target managed environments where obtaining an allocation can take quite some time to clear the queue. We used to have a "do-not-launch" flag that would allow the system to allocate and map a job, but then exit without attempting to launch it. This had been "disabled" during ORTE changes in recent months. We still had the ability to "display-map" however, but the procedure would often hang or abort as the system would attempt to resolve all network names in a hostfile. To resolve these problems, I have: 1. re-implemented the "do-not-launch" flag so it properly works. It is set by specifying --do-not-launch on the mpirun command line 2. added a --do-not-resolve option to the mpirun command line that instructs the system to not attempt to resolve network names For an example of how these can be used, consider the case where you want to build a sequential map of processes versus hostfile names via the new RMAPS seq module. It will be a big job, so you would like to ensure that the map is correct before (a) sitting in a queue for hours/days waiting to get an allocation, and (b) finding out it is wrong and having to abort. What you can do is use these new options to build and test your map -without- getting an allocation by: 1. build a hostfile that describes your desired mapping - it would have a list of host names in rank order of where you want a process to go. These hosts can have any names - we won't be trying to resolve them, so the fact that they are not necessarily reachable on the network is irrelevant. 2. do an mpirun of your job, including -mca rmaps seq -hostfile my_hosts --do-not-launch --do-not-resolve --display-map on the cmd line. This instructs mpirun to use the seq mapper, which will subsequently use the specified hostfile to do the mapping. It also tells mpirun to display the resulting map so you can see where your procs would have gone, but to not attempt to find them on the network and to -not- attempt to launch the job. What you'll get is a display node-by-node of what proc ranks are assigned to that node. Once you get this looking the way you want, you can then simply submit the job to your target cluster with confidence that the procs will be mapped the way you wanted. Hope that helps Ralph
