[slurm-users] requesting entire vs. partial nodes

[Chris Samuel]

On Saturday, 20 October 2018 9:57:16 AM AEDT Noam Bernstein wrote:

> If not, is there another way to do this?

You can use --exclusive for jobs that want whole nodes.

You will likely also want to use:

SelectTypeParameters=CR_Core_Memory,CR_ONE_TASK_PER_CORE

to ensure jobs are given one core (with all its associated threads) per task.

Also set DefMemPerCPU so that jobs get allocated a default amount of RAM per 
core if they forget to ask for it.

> And however we achieve this, how does slurm decide what order to assign
> nodes to jobs in the presence of jobs that don't take entire nodes.  If we
> have a 2 16 core nodes and two 8 task jobs, are they going to be packed
> into a single node, or each on its own node (leaving no free node for
> another 16 task job that requires an entire node)?

As long as you don't use CR_LLN (least loaded node) as your select parameter 
and you don't use pack_serial_at_end in SchedulerParameters then Slurm (I 
believe) is meant to use a best fit algorithm.

However, the thing that can still happen is that when you have lots of 
variable size jobs with very different walltimes you can start off with a 
nicely packed system at the beginning but holes then open up as jobs finish. 
So hopefully you'll have a nice mix of job sizes that will fit those holes.

All the best,
Chris
-- 
 Chris Samuel  :  http://www.csamuel.org/  :  Melbourne, VIC