Advanced Job Examples

Advanced Job Examples#

These are provided to give you a starting point, and give you ideas on what can be done.

Submitting Mixed Mode Jobs#

The ‘mixed mode’ (MPI+OpenMP) programming model typically involves MPI processes running across nodes and OpenMP threads upon each node with the total number of processes (MPI*OpenMP) equalling the number of physical processor cores.

Your code will need to call MPI_Init and make use of OpenMP directives. You will compile your code using an MPI wrapper and enabling OpenMP support, for example:

$ mpif90 -openmp example.f90 -o mixed.exe

You will need to determine ppn, the number of MPI processes per node, and tpp, the number of OpenMP threads per MPI process.

Additionally, you can either ask for a given number of nodes nodes or for the total number of MPI processes np. Note that ppn is related to np since ppn = np/nodes.

Your submission script would then need to contain:

#$ -V
#$ -l h_rt=01:00:00
#$ -l nodes=<nodes>, ppn=<ppn>, tpp=<tpp>
mpirun ./a.out

or

#$ -V
#$ -l h_rt=01:00:00
#$ -l np=<np>, ppn=<ppn>, tpp=<tpp>
mpirun ./a.out

There are 24 cores per node on ARC3, so you would typically ensure ppn*tpp=24. There are 40 cores per node on ARC4, so you would typically ensure ppn*tpp=40.

Example#

Using ARC4, To run an MPI+OpenMP executable mixed.exe with 80 MPI processes each launching 4 OpenMP threads, the following submission script would be needed:

#$ -V
#$ -cwd
#$ -l h_rt=01:00:00
#$ -l np=80, ppn=10, tpp=4
mpirun ./mixed.exe

This will allocate 8 nodes (=8*40=320 cores). Each node will have 10 MPI processes, each of which will have 4 OpenMP threads (so 10*4=40 processes per node in total, and 8*140=320 (=80MPI*4OpenMP) processes in total.

Alternatively, the same effect can be achieved by:

#$ -V
#$ -cwd
#$ -l h_rt=01:00:00
#$ -l nodes=8, ppn=10, tpp=4
mpirun ./mixed.exe

Note that the OMP_NUM_THREADS environment variable is automatically set by the batch system and so you do not need to set this in your environment.

Job Dependencies#

The SGE scheduler allows you to submit a job but then hold them in the queue until certain job dependencies are met, ie. it will hold the job until a previous job (or number of jobs have completed).

To do this, submit the first job as normal:

$ qsub job1.sh

As usual, the scheduler will give you a job ID <jobid>.

If you then want to submit another job that is dependent on the first one completing, use the -hold_jid option for qsub:

$ qsub -hold_jid <jobid> job2.sh

Job 2 will remain in the queue until job 1 has completed.

Alternatively, if you have given the job a name (using the -N option), then you can put a hold on subsequent jobs using the name instead:

$ qsub -hold_jid <jobname> job2.sh

If you give several jobs the same name, then the job will be held until all the named jobs have been completed. See Batch jobs for more details on hold_jid.

Restartable jobs#

SGE supports jobs that exit telling the scheduler that they’re not finished, and so should be rescheduled. This is very useful when you have a long running job that ultimately will take longer than 48 hours to complete, but you can easily save the current progress as you go along. Here is a dummy example to hopefully give you ideas on how this could be used:

#!/bin/bash
#$ -l h_rt=0:10:0

# Which subtask we're currently processing.  This script assumes we're only
# completing one subtask per SGE job, but there's no reason you couldn't
# process more.
counter=1

# Read the restartfile, if present, to continue from where we got up to
if [ -f restartfile ];then
  echo loading restart file
  . restartfile
fi

# If we detected we've been restarted, we may need to run differently, so
# here's how you could detect it.
if [[ $RESTARTED == 1 ]];then
  echo Auto-submitted job continuing
fi

# Complete a unit of work
echo Doing work - counter: $counter

# Increment the counter once we've done a unit of work
let counter++

# Write the next task number to the restartfile
echo counter=$counter > restartfile

# If we've not yet completed all our tasks, tell the scheduler that we'll need
# to run again
if [ $counter -le 10 ];then
  exit 99
fi

# We've completed all tasks, so don't restart.
echo Complete!

Non integer task array sequences#

This shows how you can run a task array with two sets of parameters where one of them is non-integer.

# Run a total of 72 tasks
#$ -t 1-72
# Put the logs into a separate directory
#$ -o logs
#$ -e logs
#$ -cwd -V
#$ -l h_rt=0:10:0

# Define array dimensions, lining up with the 72 tasks we're running
rows=18
columns=4

# Calculate row and column indexes
row_index=$(( ($SGE_TASK_ID - 1) / $columns + 1 ))
col_index=$(( ($SGE_TASK_ID - 1) % $columns + 1 ))

# Map the integer value into the floating point value we actually wanted
calculated_float=$(printf %.4f\\n "$(($col_index))e-4")

# Run the experiment passing those values in
./run_code $calculated_float $row_index
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