Hi Michael,

If your users are always going to be using whole nodes, then you're right that it might make more sense to switch to the select/linear plugin.  The primary benefit of using cons_res or cons_tres is the ability to track resources on the nodes.  As you can imagine, there is overhead associated with tracking all these resources instead of just tracking the nodes.  We have the following note in the Large Cluster Administration Guide:
-------------------------
While allocating individual processors within a node is great for smaller clusters, the overhead of keeping track of the individual processors and memory within each node adds significant overhead. For best scalability, allocate whole nodes using select/linear and avoid select/cons_res.
-------------------------
https://slurm.schedmd.com/big_sys.html

Another section with good information about differences between the plugins is the Mode of Operation section in the Select Plugin Design Guide, found here:
https://slurm.schedmd.com/select_design.html


To summarize, the differences between linear and cons_(res/tres) should be limited to the ability of the scheduler to break down the resources on the nodes.  The ability to use backfill or generic resources is broken out into other plugins so it shouldn't be much of a sacrifice to make this change.

Please let me know if you have any questions about this.

Thanks,
Ben

what needs to be in place to ensure backfill and features/constraints are working?

In order to use backfill you need to specify the SchedulerType:
SchedulerType=sched/backfill

Features and constraints don't require an additional plugin to work, you just need to have the feature(s) defined for the nodes.  

Thanks,
Ben

Thanks, request can be closed

From: bugs@schedmd.com <bugs@schedmd.com>
Sent: Wednesday, March 24, 2021 8:38 AM
To: Hebenstreit, Michael <michael.hebenstreit@intel.com>
Subject: [Bug 11186] advice needed: is SelectType=select/cons_res the right choice for us?

Comment # 3<https://bugs.schedmd.com/show_bug.cgi?id=11186#c3> on bug 11186<https://bugs.schedmd.com/show_bug.cgi?id=11186> from Ben Roberts<mailto:ben@schedmd.com>

In order to use backfill you need to specify the SchedulerType:

SchedulerType=sched/backfill



Features and constraints don't require an additional plugin to work, you just

need to have the feature(s) defined for the nodes.



Thanks,

Ben

________________________________
You are receiving this mail because:

  *   You reported the bug.

Sounds good, closing now.  Let us know if there's anything we can do to help in the future.