The time command runs a specified program and prints out timing statistics. It is useful when you want to analyse how different configuration options affect how long a program takes to complete.

Prerequisite knowledge

Before using the time command for high-level program timing, you will need to be familiar with running your program using the scheduler on the supercomputer.

Steps

To start using the time command to find out how long your program takes to run:

1. Insert the time command in front of the srun command in your jobscript. For example, if the srun line of your jobscript was:

   srun ./exampleProgram

   The updated jobscript would be:

   time srun ./exampleProgram



2. Submit your jobscript as usual using sbatch.

Result

The timing results from running the program will be appended to your job output:

<Usual output from existing program>

real 0m1.683s
user 0m0.031s
sys 0m0.246s

The time command has appended timings after the program output:

• real time is the total time the job took to run
• user time is the time the program spent executing parts of the code written by the programmer
• system time is the time the program spent executing underlying system calls in the operating system for the program

The user and system time may not add up to the real time, as there may be other programs running. For example, processes that are part of the operating system may be running in the background.

Related pages

• Profiling
• Job Scheduling