[slurm-users] Job flexibility with cons_tres

[Aaron Jackson]

Similar problem in the cluster I look after. I have a job_submit script
which adds certain nodes to the job's excluded nodes list based on each
node's number of cpus per gpus. This basically solved problem with
fragmentation entirely. The problem is that cons_tres seems to think
(for example) that an 8 core job needing one GPU would be a good fit for
an 8 core machine with four GPUs, leaving three GPUs unused - this would
appear as "alloc". In such a case, you'd want to exclude that node since
there are actually only 2 cores per GPU. This will push it onto a node
with more cores per GPU.

Ours test is something like:

          (job cpus / job gpus) > (node cpus / node gpus) * 1.2

which allows 20% or so, since there will also be a certain percentage of
jobs which need several GPUs but only a couple of cores. It's fairly
simple to implement with the lua submit plugin.

For newer versions of Slurm I believe it is necessary to check both tres
per task and tres per node. Fortunately only one should be set. I'm not
sure about the --gpus flag, we're still using --gres.

Cheers,
Aaron

On  8 February 2021 at 11:36 GMT, Ansgar Esztermann-Kirchner wrote:

> Hello List,
>
> we're running a heterogeneous cluster (just x86_64, but a lot of
> different node types from 8 to 64 HW threads, 1 to 4 GPUs).
> Our processing power (for our main application, at least) is 
> exclusively provided by the GPUs, so cons_tres looks quite promising:
> depending on the size of the job, request an appropriate number of
> GPUs. Of course, you have to request some CPUs as well -- ideally,
> evenly distributed among the GPUs (e.g. 10 per GPU on a 20-core, 2-GPU
> node; 16 on a 64-core, 4-GPU node).
> Of course, one could use different partitions for different nodes, and
> then submit individual jobs with CPU requests tailored to one such
> partition, but I'd prefer a more flexible approach where a given job
> could run on any large enough node.
>
> Is there anyone with a similar setup? Any config options I've missed,
> or do you have a work-around?
>
> Thanks,
>
> A.


-- 
Research Fellow
School of Computer Science
University of Nottingham



This message and any attachment are intended solely for the addressee
and may contain confidential information. If you have received this
message in error, please contact the sender and delete the email and
attachment. 

Any views or opinions expressed by the author of this email do not
necessarily reflect the views of the University of Nottingham. Email
communications with the University of Nottingham may be monitored 
where permitted by law.