[slurm-users] What is the complete logic to calculate node number in job_submit.lua

[Ole Holm Nielsen]

On 9/26/22 08:48, taleintervenor at sjtu.edu.cn wrote:
> When designing restriction in job_submit.lua, I found there is no member 
> in job_desc struct can directly be used to determine the node number 
> finally allocated to a job. The *job_desc.min_nodes *seem to be a close 
> answer, but it will be 0xFFFFFFFE when user not specify –node option. Then 
> in such case we think we can use *job_desc.num_tasks* and 
> *job_desc.ntasks_per_node *to calculate node number. But again, we find 
> *ntasks_per_node* may also be default value 0xFFFE if user not specify 
> related option.

The hex-values which you quote are actually defined as symbols in Slurm as 
slurm.NO_VAL16, slurm.NO_VAL, and slurm.NO_VAL64 which are easier to 
understand :-)  See my notes in 
https://wiki.fysik.dtu.dk/niflheim/Slurm_configuration#lua-functions-for-the-job-submit-plugin

> So what is the complete and elegant way to predict the job node number in 
> job_submit.lua in all case, no matter how user write their submit options?

The sbatch command provides defaults for nodes and tasks, if these are not 
defined in the user's job script, see the sbatch manual page:

> If -N is not specified, the  default behavior  is  to  allocate enough nodes to satisfy the requested resources as expressed by per-job  specification  options,  e.g. -n,  -c  and --gpus.  

and

> -n The default is one task per node, but note that the --cpus-per-task option will change this default.

Therefore you do not need to guess the number of nodes and tasks in your 
job_submit.lua script.

/Ole