NEC Cluster Batch System (laki + laki2)

The only way to start a parallel job on the compute nodes of this cluster is to use the portable batch system (Torque).

Policies for usage of the queues for the batch system

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Submit a batch job

You will get each requested node for your exclusive usage. There are 2 methods to use the batch system:

• interactive batch jobs:

if requested resources are available, the job starts a interactive shell immediately. For interactive access the qsub command has the option -I example:

qsub -I ...

• normal batch jobs:

jobs will be started by the MOAB scheduler after passing some rules configured by the administrator (FAIRSHARE, BACKFILLING, ...).

Command for submitting a batch job request

A short explanation follows here. For detailed information, see the man pages or the documentation in the WWW.

man qsub
man pbs_resources
man pbs

Command to submit a batch job

qsub <option>

On success, the qsub command returns a request ID.

You have to specify the resources you need for your batch job. These resources are specified by including them in the -l option argument on the qsub command or in the PBS job script. There are 2 important resources you need to specify:

1. nodes=<number of nodes>:<feature>

To distinguish between different nodes, features are assigned to each node. These features describe the properties of each node. Please do only use exactly 1 feature for each node type.

Available node:

feature	describes	notes
nehalem	2 quad core-CPU per node
tesla	nehalem nodes with a tesla GPU
mem12gb	nehalem node with 12GB memory
mem24gb	nehalem node with 24GB memory
mem48gb	nehalem node with 48GB memory

Multi nodes can be specified using a +:

nodes=2:tesla+3:nehalem

The example above will allocate 2 nodes with feature tesla and 3 nodes with feature nehalem.

2. walltime=<time>

Usage of multi-socket nodes and multi-core cpus

The batch system takes into account the number of cpus and nodes (summarized PE) for each node when assigning resources.

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The resource request feature nodes. If the request has no option for the number of PE per node (ppn) set, then the system assumes that the requested nodes is equal the number of PE's. The batch system allocates a number of nodes that in total fulfill the sum of requested PE.

Example:

 qsub -l nodes=2:nehalem ./myscript

The batch system allocates two node of feature nehalem. The file ${PBS_NODEFILE} contains:

 node1
 node2

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The ressource request feature nodes, Option ppn. If the request has the option ppn defined, then it is possible to allocate the defined PE's on a node. This option especially allow OpenMPI to place the MPI processes of ranks on a shared node or alternatively on distributed nodes.

Example:

 qsub -l nodes=2:nehalem:ppn=2+1:nehalem:ppn=3 ./myscript

The batch system allocates 2 nodes of feature nehalem each for 2 PE's and 1 node of feature nehalem for 3 PE's. Then the file ${PBS_NODEFILE} contains:

 node1
 node1
 node2
 node2
 node3
 node3
 node3

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The resource request feature nodes, option pmem. For special applications it will be useful to allocate only 1 PE per node. In this case you need a little trick, because the batch system handle the option ppn=1 like the requests without this option (see the first example). Therefore you have to define an additional option in your request. A simple way to do this is to request the maximum of the node's memory.

Example:

 qsub -l nodes=2:nehalem,pmem=11gb ./myscript

The batch system allocates 2 nodes of feature nehalem. Each of the nodes with feature nehalem have 12GByte RAM installed, so the batch system is constrained to allocate 2 nodes. And the file ${PBS_NODEFILE} should look like this:

 node1
 node2

Defaults for Ressource Requests

If you don't set the resources for your job request, then you will get default resource limits for your job.

feature	value	notes
walltime	00:10:00
nodes	1
ppn	1

Please select your resource requests carefull. The higher your specified resource limits the lower the job priority. See also NEC Nehalem Cluster QueuePolicies.

To have the same environmental settings (exported environment) of your current session in your batchjob, the qsub command needs the option argument -V.

Usage of a Reservation

For nodes which are reserved for special groups or users, you need to specify an additional option for this reservation:

E.g. a reservation named john.1 will be used with following command:

qsub -l nodes=1:nehalem,walltime=1:00 -W x=FLAGS:ADVRES:john.1 testjob.cmd

Examples for PBS options in job scripts

You can submit batch jobs using qsub. A very simple qsub script for a MPI job with PBS (Torque) directives (#PBS ...) for the options of qsub looks like this:

#!/bin/bash
#
# Simple PBS batch script that reserves two cpus and runs one
# MPI process on each node)
# The default walltime is 10min !
#
#PBS -l nodes=2:nehalem
cd $HOME/testdir
mpirun -np 2 -hostfile $PBS_NODEFILE ./mpitest

VERY important is that you specify a shell in the first line of your batch script.

VERY important in case you use the openmpi module is to omit the -hostfile option. Otherwise an error will occur like

[n110402:02618] pls:tm: failed to poll for a spawned proc, return status = 17002
[n110402:02618] [0,0,0] ORTE_ERROR_LOG: In errno in file ../../../../../orte/mca/rmgr/urm/rmgr_urm.c at line 462
[n110402:02618] mpirun: spawn failed with errno=-11

If you want to use two MPI processes on each node this can be done like this:

#!/bin/bash
#
# Simple PBS batch script that reserves two nodes and runs a
# MPI program on four processors (two on each node)
# The default walltime is 10min !
#
#PBS -l nodes=2:nehalem:ppn=2
cd $HOME/testdir
mpirun -np 4 -hostfile machines ./mpitest

If you need 2h wall time and one node you can use the following script:

#
# Simple PBS batch script that runs a scalar job using 2h
#
#PBS -l nodes=1:nehalem,walltime=2:00:00
cd $HOME/jobdir
./my_executable

Examples for starting batch jobs:

• Starting a script with all options specified inside the script file

  qsub <script>

• Starting a script using 3 nodes and a real time of 2 hours:

  qsub -l nodes=3:nehalem,walltime=2:00:00 <script>

• Starting a script using 5 cluster nodes using 4 processors on each node with PBS Feature nehalem:

  qsub -l nodes=5:nehalem:ppn=4,walltime=2:00:00 <script>

• Starting a script using 1 cluster node with PBS Feature mem24gb and 5 processors with PBS Feature mem12gb and real job time of 1.5 hours:

  qsub -l nodes=1:mem24gb+5:mem12gb,walltime=1:30:00 <script>

• Starting a interactive batch job using 5 processors with a job real time of 300 seconds:

  qsub -I -l nodes=5:nehalem,walltime=300

  For interactive Batch jobs, you don't need a script.sh file. If the requested resources are available, you will get an interactive shell on one of the allocated compute nodes. Which nodes are allocated can be shown with the command cat $PBS_NODEFILE on the batch job shell or with the PBS status command qstat -n on the master node.

  You can log in from the frontend or any assigned node to all other assigned nodes by

  ssh <nodename>

  If you exit the automatically established interactive shell to the node, it will be assumed that you finished your job and all other connections to the nodes will be terminated.

• Possibilities to request 4 cluster nodes (with feature 'nehalem' i.e. 32 processors).

  qsub -l nodes=4:nehalem:ppn=8 <script>

  qsub -l nodes=4:nehalem:pmem=11gb <script>

  The difference between both job submisson kinds is in the content of PBS_NODEFILE.

• Starting a script which should run on other Account ID: First you have to know which Account ID's (groupnames) are valid for your login:

  id

  Choose a valid groupname for your job:

  qsub -l nodes=5:nehalem,walltime=300 -W group_list=<groupname>

Get the batch job status

Available commands

qstat [options]
showq [options] (showq -h for details)
nstat

For detailed informations, see man pages:

man qstat
man pbsnodes

Examples

list all batch jobs:

qstat -a

lists all batch queues with resource limit settings:

qstat -q

lists node information of a batch job ID:

qstat -n <JOB_ID>

lists detailed information of a batch job ID:

qstat -f <JOB_ID>

lists information of the PBS node status:

pbsnodes -a
pbsnodes -l

gives informatioin of PBS node and job status:

nstat

DISPLAY: X11 applications on interactive batch jobs

For X11 applications you need to have SSH X11 Forwarding enabled. This is usually activated per default. But to be sure you can set 'ForwardX11 yes' in your $HOME/.ssh/config. To have the same DISPLAY of your current session in your batchjob, the qsub command needs the option argument -X.

frontend> qsub -l nodes=2:nehalem,walltime=300 -X -I