The short answer

Slightly more than what your job requires.

The long answer

You have to work out what your job requires, then request slightly more than this. The rest of this section details some possible strategies to work out how much resources your job uses.

CPUs or Cores

The number of CPUs you should request depends on how many CPUs your program can use at once. Most off-the-shelf programs come with an option specifying how many CPUs it will use at one time. Sometimes these may be called "threads" instead of CPUs. Whatever option you pick, you must make sure the number of CPUs requested in your program matches the number of CPUs in your PBS script, otherwise you will leave CPUs sitting idle, or you will oversubscribe CPUs, resulting in massive slowdown of your computation.

Walltime

Submit a test job to Artemis that